* [PATCH v4 01/12] aio-posix: fix race between io_uring CQE and AioHandler deletion
2025-09-10 17:56 [PATCH v4 00/12] aio: add the aio_add_sqe() io_uring API Stefan Hajnoczi
@ 2025-09-10 17:56 ` Stefan Hajnoczi
2025-10-09 14:16 ` Kevin Wolf
2025-09-10 17:56 ` [PATCH v4 02/12] aio-posix: keep polling enabled with fdmon-io_uring.c Stefan Hajnoczi
` (10 subsequent siblings)
11 siblings, 1 reply; 25+ messages in thread
From: Stefan Hajnoczi @ 2025-09-10 17:56 UTC (permalink / raw)
To: qemu-devel
Cc: Aarushi Mehta, Fam Zheng, Stefano Garzarella, Hanna Czenczek,
eblake, Stefan Hajnoczi, Kevin Wolf, qemu-block, hibriansong,
Stefan Weil, Paolo Bonzini
When an AioHandler is enqueued on ctx->submit_list for removal, the
fill_sq_ring() function will submit an io_uring POLL_REMOVE operation to
cancel the in-flight POLL_ADD operation.
There is a race when another thread enqueues an AioHandler for deletion
on ctx->submit_list when the POLL_ADD CQE has already appeared. In that
case POLL_REMOVE is unnecessary. The code already handled this, but
forgot that the AioHandler itself is still on ctx->submit_list when the
POLL_ADD CQE is being processed. It's unsafe to delete the AioHandler at
that point in time (use-after-free).
Solve this problem by keeping the AioHandler alive but setting a flag so
that it will be deleted by fill_sq_ring() when it runs.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
util/fdmon-io_uring.c | 33 ++++++++++++++++++++++++++-------
1 file changed, 26 insertions(+), 7 deletions(-)
diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c
index b0d68bdc44..ad89160f31 100644
--- a/util/fdmon-io_uring.c
+++ b/util/fdmon-io_uring.c
@@ -52,9 +52,10 @@ enum {
FDMON_IO_URING_ENTRIES = 128, /* sq/cq ring size */
/* AioHandler::flags */
- FDMON_IO_URING_PENDING = (1 << 0),
- FDMON_IO_URING_ADD = (1 << 1),
- FDMON_IO_URING_REMOVE = (1 << 2),
+ FDMON_IO_URING_PENDING = (1 << 0),
+ FDMON_IO_URING_ADD = (1 << 1),
+ FDMON_IO_URING_REMOVE = (1 << 2),
+ FDMON_IO_URING_DELETE_AIO_HANDLER = (1 << 3),
};
static inline int poll_events_from_pfd(int pfd_events)
@@ -218,6 +219,16 @@ static void fill_sq_ring(AioContext *ctx)
if (flags & FDMON_IO_URING_REMOVE) {
add_poll_remove_sqe(ctx, node);
}
+ if (flags & FDMON_IO_URING_DELETE_AIO_HANDLER) {
+ /*
+ * process_cqe() sets this flag after ADD and REMOVE have been
+ * cleared. They cannot be set again, so they must be clear.
+ */
+ assert(!(flags & FDMON_IO_URING_ADD));
+ assert(!(flags & FDMON_IO_URING_REMOVE));
+
+ QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted);
+ }
}
}
@@ -241,7 +252,12 @@ static bool process_cqe(AioContext *ctx,
*/
flags = qatomic_fetch_and(&node->flags, ~FDMON_IO_URING_REMOVE);
if (flags & FDMON_IO_URING_REMOVE) {
- QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted);
+ if (flags & FDMON_IO_URING_PENDING) {
+ /* Still on ctx->submit_list, defer deletion until fill_sq_ring() */
+ qatomic_or(&node->flags, FDMON_IO_URING_DELETE_AIO_HANDLER);
+ } else {
+ QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted);
+ }
return false;
}
@@ -347,10 +363,13 @@ void fdmon_io_uring_destroy(AioContext *ctx)
unsigned flags = qatomic_fetch_and(&node->flags,
~(FDMON_IO_URING_PENDING |
FDMON_IO_URING_ADD |
- FDMON_IO_URING_REMOVE));
+ FDMON_IO_URING_REMOVE |
+ FDMON_IO_URING_DELETE_AIO_HANDLER));
- if (flags & FDMON_IO_URING_REMOVE) {
- QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted);
+ if ((flags & FDMON_IO_URING_REMOVE) ||
+ (flags & FDMON_IO_URING_DELETE_AIO_HANDLER)) {
+ QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers,
+ node, node_deleted);
}
QSLIST_REMOVE_HEAD_RCU(&ctx->submit_list, node_submitted);
--
2.51.0
^ permalink raw reply related [flat|nested] 25+ messages in thread* Re: [PATCH v4 01/12] aio-posix: fix race between io_uring CQE and AioHandler deletion
2025-09-10 17:56 ` [PATCH v4 01/12] aio-posix: fix race between io_uring CQE and AioHandler deletion Stefan Hajnoczi
@ 2025-10-09 14:16 ` Kevin Wolf
0 siblings, 0 replies; 25+ messages in thread
From: Kevin Wolf @ 2025-10-09 14:16 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Aarushi Mehta, Fam Zheng, Stefano Garzarella,
Hanna Czenczek, eblake, qemu-block, hibriansong, Stefan Weil,
Paolo Bonzini
Am 10.09.2025 um 19:56 hat Stefan Hajnoczi geschrieben:
> When an AioHandler is enqueued on ctx->submit_list for removal, the
> fill_sq_ring() function will submit an io_uring POLL_REMOVE operation to
> cancel the in-flight POLL_ADD operation.
>
> There is a race when another thread enqueues an AioHandler for deletion
> on ctx->submit_list when the POLL_ADD CQE has already appeared. In that
> case POLL_REMOVE is unnecessary. The code already handled this, but
> forgot that the AioHandler itself is still on ctx->submit_list when the
> POLL_ADD CQE is being processed. It's unsafe to delete the AioHandler at
> that point in time (use-after-free).
>
> Solve this problem by keeping the AioHandler alive but setting a flag so
> that it will be deleted by fill_sq_ring() when it runs.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
^ permalink raw reply [flat|nested] 25+ messages in thread
* [PATCH v4 02/12] aio-posix: keep polling enabled with fdmon-io_uring.c
2025-09-10 17:56 [PATCH v4 00/12] aio: add the aio_add_sqe() io_uring API Stefan Hajnoczi
2025-09-10 17:56 ` [PATCH v4 01/12] aio-posix: fix race between io_uring CQE and AioHandler deletion Stefan Hajnoczi
@ 2025-09-10 17:56 ` Stefan Hajnoczi
2025-10-09 14:19 ` Kevin Wolf
2025-09-10 17:56 ` [PATCH v4 03/12] tests/unit: skip test-nested-aio-poll with io_uring Stefan Hajnoczi
` (9 subsequent siblings)
11 siblings, 1 reply; 25+ messages in thread
From: Stefan Hajnoczi @ 2025-09-10 17:56 UTC (permalink / raw)
To: qemu-devel
Cc: Aarushi Mehta, Fam Zheng, Stefano Garzarella, Hanna Czenczek,
eblake, Stefan Hajnoczi, Kevin Wolf, qemu-block, hibriansong,
Stefan Weil, Paolo Bonzini, Chao Gao
Commit 816a430c517e ("util/aio: Defer disabling poll mode as long as
possible") kept polling enabled when the event loop timeout is 0. Since
there is no timeout the event loop will continue immediately and the
overhead of disabling and re-enabling polling can be avoided.
fdmon-io_uring.c is unable to take advantage of this optimization
because its ->need_wait() function returns true whenever there are new
io_uring SQEs to submit:
if (timeout || ctx->fdmon_ops->need_wait(ctx)) {
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Polling will be disabled even when timeout == 0.
Extend the optimization to handle the case when need_wait() returns true
and timeout == 0.
Cc: Chao Gao <chao.gao@intel.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
util/aio-posix.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/util/aio-posix.c b/util/aio-posix.c
index 2e0a5dadc4..824fdc34cc 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -559,7 +559,14 @@ static bool run_poll_handlers(AioContext *ctx, AioHandlerList *ready_list,
elapsed_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - start_time;
max_ns = qemu_soonest_timeout(*timeout, max_ns);
assert(!(max_ns && progress));
- } while (elapsed_time < max_ns && !ctx->fdmon_ops->need_wait(ctx));
+
+ if (ctx->fdmon_ops->need_wait(ctx)) {
+ if (fdmon_supports_polling(ctx)) {
+ *timeout = 0; /* stay in polling mode */
+ }
+ break;
+ }
+ } while (elapsed_time < max_ns);
if (remove_idle_poll_handlers(ctx, ready_list,
start_time + elapsed_time)) {
@@ -722,7 +729,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
* up IO threads when some work becomes pending. It is essential to
* avoid hangs or unnecessary latency.
*/
- if (poll_set_started(ctx, &ready_list, false)) {
+ if (timeout && poll_set_started(ctx, &ready_list, false)) {
timeout = 0;
progress = true;
}
--
2.51.0
^ permalink raw reply related [flat|nested] 25+ messages in thread* Re: [PATCH v4 02/12] aio-posix: keep polling enabled with fdmon-io_uring.c
2025-09-10 17:56 ` [PATCH v4 02/12] aio-posix: keep polling enabled with fdmon-io_uring.c Stefan Hajnoczi
@ 2025-10-09 14:19 ` Kevin Wolf
0 siblings, 0 replies; 25+ messages in thread
From: Kevin Wolf @ 2025-10-09 14:19 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Aarushi Mehta, Fam Zheng, Stefano Garzarella,
Hanna Czenczek, eblake, qemu-block, hibriansong, Stefan Weil,
Paolo Bonzini, Chao Gao
Am 10.09.2025 um 19:56 hat Stefan Hajnoczi geschrieben:
> Commit 816a430c517e ("util/aio: Defer disabling poll mode as long as
> possible") kept polling enabled when the event loop timeout is 0. Since
> there is no timeout the event loop will continue immediately and the
> overhead of disabling and re-enabling polling can be avoided.
>
> fdmon-io_uring.c is unable to take advantage of this optimization
> because its ->need_wait() function returns true whenever there are new
> io_uring SQEs to submit:
>
> if (timeout || ctx->fdmon_ops->need_wait(ctx)) {
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Polling will be disabled even when timeout == 0.
>
> Extend the optimization to handle the case when need_wait() returns true
> and timeout == 0.
>
> Cc: Chao Gao <chao.gao@intel.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
^ permalink raw reply [flat|nested] 25+ messages in thread
* [PATCH v4 03/12] tests/unit: skip test-nested-aio-poll with io_uring
2025-09-10 17:56 [PATCH v4 00/12] aio: add the aio_add_sqe() io_uring API Stefan Hajnoczi
2025-09-10 17:56 ` [PATCH v4 01/12] aio-posix: fix race between io_uring CQE and AioHandler deletion Stefan Hajnoczi
2025-09-10 17:56 ` [PATCH v4 02/12] aio-posix: keep polling enabled with fdmon-io_uring.c Stefan Hajnoczi
@ 2025-09-10 17:56 ` Stefan Hajnoczi
2025-10-09 14:20 ` Kevin Wolf
2025-09-10 17:56 ` [PATCH v4 04/12] aio-posix: integrate fdmon into glib event loop Stefan Hajnoczi
` (8 subsequent siblings)
11 siblings, 1 reply; 25+ messages in thread
From: Stefan Hajnoczi @ 2025-09-10 17:56 UTC (permalink / raw)
To: qemu-devel
Cc: Aarushi Mehta, Fam Zheng, Stefano Garzarella, Hanna Czenczek,
eblake, Stefan Hajnoczi, Kevin Wolf, qemu-block, hibriansong,
Stefan Weil, Paolo Bonzini
test-nested-aio-poll relies on internal details of how fdmon-poll.c
handles AioContext polling. Skip it when other fdmon implementations are
in use.
Note that this test is only built on POSIX systems so it is safe to
include "util/aio-posix.h".
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
tests/unit/test-nested-aio-poll.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/tests/unit/test-nested-aio-poll.c b/tests/unit/test-nested-aio-poll.c
index d8fd92c43b..45484e745b 100644
--- a/tests/unit/test-nested-aio-poll.c
+++ b/tests/unit/test-nested-aio-poll.c
@@ -15,6 +15,7 @@
#include "qemu/osdep.h"
#include "block/aio.h"
#include "qapi/error.h"
+#include "util/aio-posix.h"
typedef struct {
AioContext *ctx;
@@ -71,6 +72,12 @@ static void test(void)
.ctx = aio_context_new(&error_abort),
};
+ if (td.ctx->fdmon_ops != &fdmon_poll_ops) {
+ /* This test is tied to fdmon-poll.c */
+ g_test_skip("fdmon_poll_ops not in use");
+ return;
+ }
+
qemu_set_current_aio_context(td.ctx);
/* Enable polling */
--
2.51.0
^ permalink raw reply related [flat|nested] 25+ messages in thread* Re: [PATCH v4 03/12] tests/unit: skip test-nested-aio-poll with io_uring
2025-09-10 17:56 ` [PATCH v4 03/12] tests/unit: skip test-nested-aio-poll with io_uring Stefan Hajnoczi
@ 2025-10-09 14:20 ` Kevin Wolf
0 siblings, 0 replies; 25+ messages in thread
From: Kevin Wolf @ 2025-10-09 14:20 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Aarushi Mehta, Fam Zheng, Stefano Garzarella,
Hanna Czenczek, eblake, qemu-block, hibriansong, Stefan Weil,
Paolo Bonzini
Am 10.09.2025 um 19:56 hat Stefan Hajnoczi geschrieben:
> test-nested-aio-poll relies on internal details of how fdmon-poll.c
> handles AioContext polling. Skip it when other fdmon implementations are
> in use.
>
> Note that this test is only built on POSIX systems so it is safe to
> include "util/aio-posix.h".
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
Maybe give a specific example of what fails with other fdmon
implementations?
Could we change the test to downgrade to fdmon-poll instead of skipping
the test entirely?
Kevin
^ permalink raw reply [flat|nested] 25+ messages in thread
* [PATCH v4 04/12] aio-posix: integrate fdmon into glib event loop
2025-09-10 17:56 [PATCH v4 00/12] aio: add the aio_add_sqe() io_uring API Stefan Hajnoczi
` (2 preceding siblings ...)
2025-09-10 17:56 ` [PATCH v4 03/12] tests/unit: skip test-nested-aio-poll with io_uring Stefan Hajnoczi
@ 2025-09-10 17:56 ` Stefan Hajnoczi
2025-10-09 15:25 ` Kevin Wolf
2025-09-10 17:56 ` [PATCH v4 05/12] aio: remove aio_context_use_g_source() Stefan Hajnoczi
` (7 subsequent siblings)
11 siblings, 1 reply; 25+ messages in thread
From: Stefan Hajnoczi @ 2025-09-10 17:56 UTC (permalink / raw)
To: qemu-devel
Cc: Aarushi Mehta, Fam Zheng, Stefano Garzarella, Hanna Czenczek,
eblake, Stefan Hajnoczi, Kevin Wolf, qemu-block, hibriansong,
Stefan Weil, Paolo Bonzini
AioContext's glib integration only supports ppoll(2) file descriptor
monitoring. epoll(7) and io_uring(7) disable themselves and switch back
to ppoll(2) when the glib event loop is used. The main loop thread
cannot use epoll(7) or io_uring(7) because it always uses the glib event
loop.
Future QEMU features may require io_uring(7). One example is uring_cmd
support in FUSE exports. Each feature could create its own io_uring(7)
context and integrate it into the event loop, but this is inefficient
due to extra syscalls. It would be more efficient to reuse the
AioContext's existing fdmon-io_uring.c io_uring(7) context because
fdmon-io_uring.c will already be active on systems where Linux io_uring
is available.
In order to keep fdmon-io_uring.c's AioContext operational even when the
glib event loop is used, extend FDMonOps with an API similar to
GSourceFuncs so that file descriptor monitoring can integrate into the
glib event loop.
A quick summary of the GSourceFuncs API:
- prepare() is called each event loop iteration before waiting for file
descriptors and timers.
- check() is called to determine whether events are ready to be
dispatched after waiting.
- dispatch() is called to process events.
More details here: https://docs.gtk.org/glib/struct.SourceFuncs.html
Move the ppoll(2)-specific code from aio-posix.c into fdmon-poll.c and
also implement epoll(7)- and io_uring(7)-specific file descriptor
monitoring code for glib event loops.
Note that it's still faster to use aio_poll() rather than the glib event
loop since glib waits for file descriptor activity with ppoll(2) and
does not support adaptive polling. But at least epoll(7) and io_uring(7)
now work in glib event loops.
Splitting this into multiple commits without temporarily breaking
AioContext proved difficult so this commit makes all the changes. The
next commit will remove the aio_context_use_g_source() API because it is
no longer needed.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
include/block/aio.h | 36 ++++++++++++++++++
util/aio-posix.h | 5 +++
tests/unit/test-aio.c | 7 +++-
util/aio-posix.c | 69 ++++++++-------------------------
util/fdmon-epoll.c | 52 ++++++++++++++++++++++---
util/fdmon-io_uring.c | 44 +++++++++++++++++++++-
util/fdmon-poll.c | 88 ++++++++++++++++++++++++++++++++++++++++++-
7 files changed, 239 insertions(+), 62 deletions(-)
diff --git a/include/block/aio.h b/include/block/aio.h
index 99ff48420b..39ed86d14d 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -106,6 +106,38 @@ typedef struct {
* Returns: true if ->wait() should be called, false otherwise.
*/
bool (*need_wait)(AioContext *ctx);
+
+ /*
+ * gsource_prepare:
+ * @ctx: the AioContext
+ *
+ * Prepare for the glib event loop to wait for events instead of the usual
+ * ->wait() call. See glib's GSourceFuncs->prepare().
+ */
+ void (*gsource_prepare)(AioContext *ctx);
+
+ /*
+ * gsource_check:
+ * @ctx: the AioContext
+ *
+ * Called by the glib event loop from glib's GSourceFuncs->check() after
+ * waiting for events.
+ *
+ * Returns: true when ready to be dispatched.
+ */
+ bool (*gsource_check)(AioContext *ctx);
+
+ /*
+ * gsource_dispatch:
+ * @ctx: the AioContext
+ * @ready_list: list for handlers that become ready
+ *
+ * Place ready AioHandlers on ready_list. Called as part of the glib event
+ * loop from glib's GSourceFuncs->dispatch().
+ *
+ * Called with list_lock incremented.
+ */
+ void (*gsource_dispatch)(AioContext *ctx, AioHandlerList *ready_list);
} FDMonOps;
/*
@@ -222,6 +254,7 @@ struct AioContext {
/* State for file descriptor monitoring using Linux io_uring */
struct io_uring fdmon_io_uring;
AioHandlerSList submit_list;
+ gpointer io_uring_fd_tag;
#endif
/* TimerLists for calling timers - one per clock type. Has its own
@@ -254,6 +287,9 @@ struct AioContext {
/* epoll(7) state used when built with CONFIG_EPOLL */
int epollfd;
+ /* The GSource unix fd tag for epollfd */
+ gpointer epollfd_tag;
+
const FDMonOps *fdmon_ops;
};
diff --git a/util/aio-posix.h b/util/aio-posix.h
index 82a0201ea4..f9994ed79e 100644
--- a/util/aio-posix.h
+++ b/util/aio-posix.h
@@ -47,9 +47,14 @@ void aio_add_ready_handler(AioHandlerList *ready_list, AioHandler *node,
extern const FDMonOps fdmon_poll_ops;
+/* Switch back to poll(2). list_lock must be held. */
+void fdmon_poll_downgrade(AioContext *ctx);
+
#ifdef CONFIG_EPOLL_CREATE1
bool fdmon_epoll_try_upgrade(AioContext *ctx, unsigned npfd);
void fdmon_epoll_setup(AioContext *ctx);
+
+/* list_lock must be held */
void fdmon_epoll_disable(AioContext *ctx);
#else
static inline bool fdmon_epoll_try_upgrade(AioContext *ctx, unsigned npfd)
diff --git a/tests/unit/test-aio.c b/tests/unit/test-aio.c
index e77d86be87..010d65b79a 100644
--- a/tests/unit/test-aio.c
+++ b/tests/unit/test-aio.c
@@ -527,7 +527,12 @@ static void test_source_bh_delete_from_cb(void)
g_assert_cmpint(data1.n, ==, data1.max);
g_assert(data1.bh == NULL);
- assert(g_main_context_iteration(NULL, false));
+ /*
+ * There may be up to one more iteration due to the aio_notify
+ * EventNotifier.
+ */
+ g_main_context_iteration(NULL, false);
+
assert(!g_main_context_iteration(NULL, false));
}
diff --git a/util/aio-posix.c b/util/aio-posix.c
index 824fdc34cc..9de05ee7e8 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -70,15 +70,6 @@ static AioHandler *find_aio_handler(AioContext *ctx, int fd)
static bool aio_remove_fd_handler(AioContext *ctx, AioHandler *node)
{
- /* If the GSource is in the process of being destroyed then
- * g_source_remove_poll() causes an assertion failure. Skip
- * removal in that case, because glib cleans up its state during
- * destruction anyway.
- */
- if (!g_source_is_destroyed(&ctx->source)) {
- g_source_remove_poll(&ctx->source, &node->pfd);
- }
-
node->pfd.revents = 0;
node->poll_ready = false;
@@ -153,7 +144,6 @@ void aio_set_fd_handler(AioContext *ctx,
} else {
new_node->pfd = node->pfd;
}
- g_source_add_poll(&ctx->source, &new_node->pfd);
new_node->pfd.events = (io_read ? G_IO_IN | G_IO_HUP | G_IO_ERR : 0);
new_node->pfd.events |= (io_write ? G_IO_OUT | G_IO_ERR : 0);
@@ -267,37 +257,13 @@ bool aio_prepare(AioContext *ctx)
poll_set_started(ctx, &ready_list, false);
/* TODO what to do with this list? */
+ ctx->fdmon_ops->gsource_prepare(ctx);
return false;
}
bool aio_pending(AioContext *ctx)
{
- AioHandler *node;
- bool result = false;
-
- /*
- * We have to walk very carefully in case aio_set_fd_handler is
- * called while we're walking.
- */
- qemu_lockcnt_inc(&ctx->list_lock);
-
- QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
- int revents;
-
- /* TODO should this check poll ready? */
- revents = node->pfd.revents & node->pfd.events;
- if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read) {
- result = true;
- break;
- }
- if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write) {
- result = true;
- break;
- }
- }
- qemu_lockcnt_dec(&ctx->list_lock);
-
- return result;
+ return ctx->fdmon_ops->gsource_check(ctx);
}
static void aio_free_deleted_handlers(AioContext *ctx)
@@ -390,10 +356,6 @@ static bool aio_dispatch_handler(AioContext *ctx, AioHandler *node)
return progress;
}
-/*
- * If we have a list of ready handlers then this is more efficient than
- * scanning all handlers with aio_dispatch_handlers().
- */
static bool aio_dispatch_ready_handlers(AioContext *ctx,
AioHandlerList *ready_list,
int64_t block_ns)
@@ -417,24 +379,18 @@ static bool aio_dispatch_ready_handlers(AioContext *ctx,
return progress;
}
-/* Slower than aio_dispatch_ready_handlers() but only used via glib */
-static bool aio_dispatch_handlers(AioContext *ctx)
-{
- AioHandler *node, *tmp;
- bool progress = false;
-
- QLIST_FOREACH_SAFE_RCU(node, &ctx->aio_handlers, node, tmp) {
- progress = aio_dispatch_handler(ctx, node) || progress;
- }
-
- return progress;
-}
-
void aio_dispatch(AioContext *ctx)
{
+ AioHandlerList ready_list = QLIST_HEAD_INITIALIZER(ready_list);
+
qemu_lockcnt_inc(&ctx->list_lock);
aio_bh_poll(ctx);
- aio_dispatch_handlers(ctx);
+
+ ctx->fdmon_ops->gsource_dispatch(ctx, &ready_list);
+
+ /* block_ns is 0 because polling is disabled in the glib event loop */
+ aio_dispatch_ready_handlers(ctx, &ready_list, 0);
+
aio_free_deleted_handlers(ctx);
qemu_lockcnt_dec(&ctx->list_lock);
@@ -766,6 +722,7 @@ void aio_context_setup(AioContext *ctx)
{
ctx->fdmon_ops = &fdmon_poll_ops;
ctx->epollfd = -1;
+ ctx->epollfd_tag = NULL;
/* Use the fastest fd monitoring implementation if available */
if (fdmon_io_uring_setup(ctx)) {
@@ -778,7 +735,11 @@ void aio_context_setup(AioContext *ctx)
void aio_context_destroy(AioContext *ctx)
{
fdmon_io_uring_destroy(ctx);
+
+ qemu_lockcnt_lock(&ctx->list_lock);
fdmon_epoll_disable(ctx);
+ qemu_lockcnt_unlock(&ctx->list_lock);
+
aio_free_deleted_handlers(ctx);
}
diff --git a/util/fdmon-epoll.c b/util/fdmon-epoll.c
index 9fb8800dde..0e78baa634 100644
--- a/util/fdmon-epoll.c
+++ b/util/fdmon-epoll.c
@@ -19,8 +19,12 @@ void fdmon_epoll_disable(AioContext *ctx)
ctx->epollfd = -1;
}
- /* Switch back */
- ctx->fdmon_ops = &fdmon_poll_ops;
+ if (ctx->epollfd_tag) {
+ g_source_remove_unix_fd(&ctx->source, ctx->epollfd_tag);
+ ctx->epollfd_tag = NULL;
+ }
+
+ fdmon_poll_downgrade(ctx);
}
static inline int epoll_events_from_pfd(int pfd_events)
@@ -93,10 +97,47 @@ out:
return ret;
}
+static void fdmon_epoll_gsource_prepare(AioContext *ctx)
+{
+ /* Do nothing */
+}
+
+static bool fdmon_epoll_gsource_check(AioContext *ctx)
+{
+ return g_source_query_unix_fd(&ctx->source, ctx->epollfd_tag) & G_IO_IN;
+}
+
+static void fdmon_epoll_gsource_dispatch(AioContext *ctx,
+ AioHandlerList *ready_list)
+{
+ AioHandler *node;
+ int ret;
+ struct epoll_event events[128];
+
+ /* Collect events and process them */
+ ret = epoll_wait(ctx->epollfd, events, ARRAY_SIZE(events), 0);
+ if (ret <= 0) {
+ return;
+ }
+ for (int i = 0; i < ret; i++) {
+ int ev = events[i].events;
+ int revents = (ev & EPOLLIN ? G_IO_IN : 0) |
+ (ev & EPOLLOUT ? G_IO_OUT : 0) |
+ (ev & EPOLLHUP ? G_IO_HUP : 0) |
+ (ev & EPOLLERR ? G_IO_ERR : 0);
+
+ node = events[i].data.ptr;
+ aio_add_ready_handler(ready_list, node, revents);
+ }
+}
+
static const FDMonOps fdmon_epoll_ops = {
.update = fdmon_epoll_update,
.wait = fdmon_epoll_wait,
.need_wait = aio_poll_disabled,
+ .gsource_prepare = fdmon_epoll_gsource_prepare,
+ .gsource_check = fdmon_epoll_gsource_check,
+ .gsource_dispatch = fdmon_epoll_gsource_dispatch,
};
static bool fdmon_epoll_try_enable(AioContext *ctx)
@@ -118,6 +159,8 @@ static bool fdmon_epoll_try_enable(AioContext *ctx)
}
ctx->fdmon_ops = &fdmon_epoll_ops;
+ ctx->epollfd_tag = g_source_add_unix_fd(&ctx->source, ctx->epollfd,
+ G_IO_IN);
return true;
}
@@ -139,12 +182,11 @@ bool fdmon_epoll_try_upgrade(AioContext *ctx, unsigned npfd)
}
ok = fdmon_epoll_try_enable(ctx);
-
- qemu_lockcnt_inc_and_unlock(&ctx->list_lock);
-
if (!ok) {
fdmon_epoll_disable(ctx);
}
+
+ qemu_lockcnt_inc_and_unlock(&ctx->list_lock);
return ok;
}
diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c
index ad89160f31..4b6dc8903f 100644
--- a/util/fdmon-io_uring.c
+++ b/util/fdmon-io_uring.c
@@ -276,6 +276,11 @@ static int process_cq_ring(AioContext *ctx, AioHandlerList *ready_list)
unsigned num_ready = 0;
unsigned head;
+ /* If the CQ overflowed then fetch CQEs with a syscall */
+ if (io_uring_cq_has_overflow(ring)) {
+ io_uring_get_events(ring);
+ }
+
io_uring_for_each_cqe(ring, head, cqe) {
if (process_cqe(ctx, ready_list, cqe)) {
num_ready++;
@@ -288,6 +293,30 @@ static int process_cq_ring(AioContext *ctx, AioHandlerList *ready_list)
return num_ready;
}
+/* This is where SQEs are submitted in the glib event loop */
+static void fdmon_io_uring_gsource_prepare(AioContext *ctx)
+{
+ fill_sq_ring(ctx);
+ if (io_uring_sq_ready(&ctx->fdmon_io_uring)) {
+ while (io_uring_submit(&ctx->fdmon_io_uring) == -EINTR) {
+ /* Keep trying if syscall was interrupted */
+ }
+ }
+}
+
+static bool fdmon_io_uring_gsource_check(AioContext *ctx)
+{
+ gpointer tag = ctx->io_uring_fd_tag;
+ return g_source_query_unix_fd(&ctx->source, tag) & G_IO_IN;
+}
+
+/* This is where CQEs are processed in the glib event loop */
+static void fdmon_io_uring_gsource_dispatch(AioContext *ctx,
+ AioHandlerList *ready_list)
+{
+ process_cq_ring(ctx, ready_list);
+}
+
static int fdmon_io_uring_wait(AioContext *ctx, AioHandlerList *ready_list,
int64_t timeout)
{
@@ -335,12 +364,17 @@ static const FDMonOps fdmon_io_uring_ops = {
.update = fdmon_io_uring_update,
.wait = fdmon_io_uring_wait,
.need_wait = fdmon_io_uring_need_wait,
+ .gsource_prepare = fdmon_io_uring_gsource_prepare,
+ .gsource_check = fdmon_io_uring_gsource_check,
+ .gsource_dispatch = fdmon_io_uring_gsource_dispatch,
};
bool fdmon_io_uring_setup(AioContext *ctx)
{
int ret;
+ ctx->io_uring_fd_tag = NULL;
+
ret = io_uring_queue_init(FDMON_IO_URING_ENTRIES, &ctx->fdmon_io_uring, 0);
if (ret != 0) {
return false;
@@ -348,6 +382,9 @@ bool fdmon_io_uring_setup(AioContext *ctx)
QSLIST_INIT(&ctx->submit_list);
ctx->fdmon_ops = &fdmon_io_uring_ops;
+ ctx->io_uring_fd_tag = g_source_add_unix_fd(&ctx->source,
+ ctx->fdmon_io_uring.ring_fd, G_IO_IN);
+
return true;
}
@@ -375,6 +412,11 @@ void fdmon_io_uring_destroy(AioContext *ctx)
QSLIST_REMOVE_HEAD_RCU(&ctx->submit_list, node_submitted);
}
- ctx->fdmon_ops = &fdmon_poll_ops;
+ g_source_remove_unix_fd(&ctx->source, ctx->io_uring_fd_tag);
+ ctx->io_uring_fd_tag = NULL;
+
+ qemu_lockcnt_lock(&ctx->list_lock);
+ fdmon_poll_downgrade(ctx);
+ qemu_lockcnt_unlock(&ctx->list_lock);
}
}
diff --git a/util/fdmon-poll.c b/util/fdmon-poll.c
index 17df917cf9..f91dc54944 100644
--- a/util/fdmon-poll.c
+++ b/util/fdmon-poll.c
@@ -72,6 +72,11 @@ static int fdmon_poll_wait(AioContext *ctx, AioHandlerList *ready_list,
/* epoll(7) is faster above a certain number of fds */
if (fdmon_epoll_try_upgrade(ctx, npfd)) {
+ QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
+ if (!QLIST_IS_INSERTED(node, node_deleted) && node->pfd.events) {
+ g_source_remove_poll(&ctx->source, &node->pfd);
+ }
+ }
npfd = 0; /* we won't need pollfds[], reset npfd */
return ctx->fdmon_ops->wait(ctx, ready_list, timeout);
}
@@ -97,11 +102,92 @@ static void fdmon_poll_update(AioContext *ctx,
AioHandler *old_node,
AioHandler *new_node)
{
- /* Do nothing, AioHandler already contains the state we'll need */
+ if (old_node && !new_node) {
+ /*
+ * If the GSource is in the process of being destroyed then
+ * g_source_remove_poll() causes an assertion failure. Skip removal in
+ * that case, because glib cleans up its state during destruction
+ * anyway.
+ */
+ if (!g_source_is_destroyed(&ctx->source)) {
+ g_source_remove_poll(&ctx->source, &old_node->pfd);
+ }
+ }
+
+ if (!old_node && new_node) {
+ g_source_add_poll(&ctx->source, &new_node->pfd);
+ }
+}
+
+static void fdmon_poll_gsource_prepare(AioContext *ctx)
+{
+ /* Do nothing */
+}
+
+static bool fdmon_poll_gsource_check(AioContext *ctx)
+{
+ AioHandler *node;
+ bool result = false;
+
+ /*
+ * We have to walk very carefully in case aio_set_fd_handler is
+ * called while we're walking.
+ */
+ qemu_lockcnt_inc(&ctx->list_lock);
+
+ QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
+ int revents = node->pfd.revents & node->pfd.events;
+
+ if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read) {
+ result = true;
+ break;
+ }
+ if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write) {
+ result = true;
+ break;
+ }
+ }
+
+ qemu_lockcnt_dec(&ctx->list_lock);
+
+ return result;
+}
+
+static void fdmon_poll_gsource_dispatch(AioContext *ctx,
+ AioHandlerList *ready_list)
+{
+ AioHandler *node;
+
+ QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
+ int revents;
+
+ revents = node->pfd.revents & node->pfd.events;
+ if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read) {
+ aio_add_ready_handler(ready_list, node, revents);
+ } else if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write) {
+ aio_add_ready_handler(ready_list, node, revents);
+ }
+ }
}
const FDMonOps fdmon_poll_ops = {
.update = fdmon_poll_update,
.wait = fdmon_poll_wait,
.need_wait = aio_poll_disabled,
+ .gsource_prepare = fdmon_poll_gsource_prepare,
+ .gsource_check = fdmon_poll_gsource_check,
+ .gsource_dispatch = fdmon_poll_gsource_dispatch,
};
+
+void fdmon_poll_downgrade(AioContext *ctx)
+{
+ AioHandler *node;
+
+ ctx->fdmon_ops = &fdmon_poll_ops;
+
+ QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
+ if (!QLIST_IS_INSERTED(node, node_deleted) && node->pfd.events) {
+ g_source_add_poll(&ctx->source, &node->pfd);
+ }
+ }
+}
--
2.51.0
^ permalink raw reply related [flat|nested] 25+ messages in thread* Re: [PATCH v4 04/12] aio-posix: integrate fdmon into glib event loop
2025-09-10 17:56 ` [PATCH v4 04/12] aio-posix: integrate fdmon into glib event loop Stefan Hajnoczi
@ 2025-10-09 15:25 ` Kevin Wolf
0 siblings, 0 replies; 25+ messages in thread
From: Kevin Wolf @ 2025-10-09 15:25 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Aarushi Mehta, Fam Zheng, Stefano Garzarella,
Hanna Czenczek, eblake, qemu-block, hibriansong, Stefan Weil,
Paolo Bonzini
Am 10.09.2025 um 19:56 hat Stefan Hajnoczi geschrieben:
> AioContext's glib integration only supports ppoll(2) file descriptor
> monitoring. epoll(7) and io_uring(7) disable themselves and switch back
> to ppoll(2) when the glib event loop is used. The main loop thread
> cannot use epoll(7) or io_uring(7) because it always uses the glib event
> loop.
>
> Future QEMU features may require io_uring(7). One example is uring_cmd
> support in FUSE exports. Each feature could create its own io_uring(7)
> context and integrate it into the event loop, but this is inefficient
> due to extra syscalls. It would be more efficient to reuse the
> AioContext's existing fdmon-io_uring.c io_uring(7) context because
> fdmon-io_uring.c will already be active on systems where Linux io_uring
> is available.
>
> In order to keep fdmon-io_uring.c's AioContext operational even when the
> glib event loop is used, extend FDMonOps with an API similar to
> GSourceFuncs so that file descriptor monitoring can integrate into the
> glib event loop.
>
> A quick summary of the GSourceFuncs API:
> - prepare() is called each event loop iteration before waiting for file
> descriptors and timers.
> - check() is called to determine whether events are ready to be
> dispatched after waiting.
> - dispatch() is called to process events.
>
> More details here: https://docs.gtk.org/glib/struct.SourceFuncs.html
>
> Move the ppoll(2)-specific code from aio-posix.c into fdmon-poll.c and
> also implement epoll(7)- and io_uring(7)-specific file descriptor
> monitoring code for glib event loops.
>
> Note that it's still faster to use aio_poll() rather than the glib event
> loop since glib waits for file descriptor activity with ppoll(2) and
> does not support adaptive polling. But at least epoll(7) and io_uring(7)
> now work in glib event loops.
>
> Splitting this into multiple commits without temporarily breaking
> AioContext proved difficult so this commit makes all the changes. The
> next commit will remove the aio_context_use_g_source() API because it is
> no longer needed.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
It looks to me like we get a lot of duplication between implementations
of .wait and the new .gsource_* callbacks. We can probably clean this up
later. In the meantime, we need to make sure that the implementations
don't diverge.
> include/block/aio.h | 36 ++++++++++++++++++
> util/aio-posix.h | 5 +++
> tests/unit/test-aio.c | 7 +++-
> util/aio-posix.c | 69 ++++++++-------------------------
> util/fdmon-epoll.c | 52 ++++++++++++++++++++++---
> util/fdmon-io_uring.c | 44 +++++++++++++++++++++-
> util/fdmon-poll.c | 88 ++++++++++++++++++++++++++++++++++++++++++-
> 7 files changed, 239 insertions(+), 62 deletions(-)
> +static void fdmon_epoll_gsource_dispatch(AioContext *ctx,
> + AioHandlerList *ready_list)
> +{
> + AioHandler *node;
> + int ret;
> + struct epoll_event events[128];
> +
> + /* Collect events and process them */
> + ret = epoll_wait(ctx->epollfd, events, ARRAY_SIZE(events), 0);
> + if (ret <= 0) {
> + return;
> + }
> + for (int i = 0; i < ret; i++) {
> + int ev = events[i].events;
> + int revents = (ev & EPOLLIN ? G_IO_IN : 0) |
> + (ev & EPOLLOUT ? G_IO_OUT : 0) |
> + (ev & EPOLLHUP ? G_IO_HUP : 0) |
> + (ev & EPOLLERR ? G_IO_ERR : 0);
> +
> + node = events[i].data.ptr;
> + aio_add_ready_handler(ready_list, node, revents);
> + }
> +}
Isn't this just fdmon_epoll_wait(ctx, ready_list, 0)?
> @@ -97,11 +102,92 @@ static void fdmon_poll_update(AioContext *ctx,
> AioHandler *old_node,
> AioHandler *new_node)
> {
> - /* Do nothing, AioHandler already contains the state we'll need */
> + if (old_node && !new_node) {
> + /*
> + * If the GSource is in the process of being destroyed then
> + * g_source_remove_poll() causes an assertion failure. Skip removal in
> + * that case, because glib cleans up its state during destruction
> + * anyway.
> + */
> + if (!g_source_is_destroyed(&ctx->source)) {
> + g_source_remove_poll(&ctx->source, &old_node->pfd);
> + }
> + }
> +
> + if (!old_node && new_node) {
> + g_source_add_poll(&ctx->source, &new_node->pfd);
> + }
> +}
I think this changes the behaviour for the case where we update a node,
i.e. old_node and new_node are both non-NULL. Previously we added the
new node and removed the old one, now you're skipping this.
Both are referring to the same file descriptor, but we're not passing
an integer here but a pointer to a heap-allocated GPollFD (which is
contined in the AioHandler). The next thing that happens in the caller
is that we free old_node.
Doesn't this cause use after free?
> +static void fdmon_poll_gsource_prepare(AioContext *ctx)
> +{
> + /* Do nothing */
> +}
> +
> +static bool fdmon_poll_gsource_check(AioContext *ctx)
> +{
> + AioHandler *node;
> + bool result = false;
> +
> + /*
> + * We have to walk very carefully in case aio_set_fd_handler is
> + * called while we're walking.
> + */
> + qemu_lockcnt_inc(&ctx->list_lock);
> +
> + QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
> + int revents = node->pfd.revents & node->pfd.events;
> +
> + if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read) {
> + result = true;
> + break;
> + }
> + if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write) {
> + result = true;
> + break;
> + }
> + }
> +
> + qemu_lockcnt_dec(&ctx->list_lock);
> +
> + return result;
> +}
> +
> +static void fdmon_poll_gsource_dispatch(AioContext *ctx,
> + AioHandlerList *ready_list)
> +{
> + AioHandler *node;
> +
> + QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
> + int revents;
> +
> + revents = node->pfd.revents & node->pfd.events;
> + if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read) {
> + aio_add_ready_handler(ready_list, node, revents);
> + } else if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write) {
> + aio_add_ready_handler(ready_list, node, revents);
> + }
Why do we need these checks? Don't we already know that if an event is
in node->pfd.events, there is a matching io_read/io_write callback, too?
This is how aio_set_fd_handler() decides which events to monitor.
If we do need them, why doesn't fdmon_poll_wait()?
> + }
> }
>
> const FDMonOps fdmon_poll_ops = {
> .update = fdmon_poll_update,
> .wait = fdmon_poll_wait,
> .need_wait = aio_poll_disabled,
> + .gsource_prepare = fdmon_poll_gsource_prepare,
> + .gsource_check = fdmon_poll_gsource_check,
> + .gsource_dispatch = fdmon_poll_gsource_dispatch,
> };
Kevin
^ permalink raw reply [flat|nested] 25+ messages in thread
* [PATCH v4 05/12] aio: remove aio_context_use_g_source()
2025-09-10 17:56 [PATCH v4 00/12] aio: add the aio_add_sqe() io_uring API Stefan Hajnoczi
` (3 preceding siblings ...)
2025-09-10 17:56 ` [PATCH v4 04/12] aio-posix: integrate fdmon into glib event loop Stefan Hajnoczi
@ 2025-09-10 17:56 ` Stefan Hajnoczi
2025-10-09 15:46 ` Kevin Wolf
2025-09-10 17:56 ` [PATCH v4 06/12] aio: free AioContext when aio_context_new() fails Stefan Hajnoczi
` (6 subsequent siblings)
11 siblings, 1 reply; 25+ messages in thread
From: Stefan Hajnoczi @ 2025-09-10 17:56 UTC (permalink / raw)
To: qemu-devel
Cc: Aarushi Mehta, Fam Zheng, Stefano Garzarella, Hanna Czenczek,
eblake, Stefan Hajnoczi, Kevin Wolf, qemu-block, hibriansong,
Stefan Weil, Paolo Bonzini
There is no need for aio_context_use_g_source() now that epoll(7) and
io_uring(7) file descriptor monitoring works with the glib event loop.
AioContext doesn't need to be notified that GSource is being used.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
include/block/aio.h | 3 ---
tests/unit/test-nested-aio-poll.c | 6 ------
util/aio-posix.c | 12 ------------
util/aio-win32.c | 4 ----
util/async.c | 1 -
5 files changed, 26 deletions(-)
diff --git a/include/block/aio.h b/include/block/aio.h
index 39ed86d14d..1657740a0e 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -728,9 +728,6 @@ void aio_context_setup(AioContext *ctx);
*/
void aio_context_destroy(AioContext *ctx);
-/* Used internally, do not call outside AioContext code */
-void aio_context_use_g_source(AioContext *ctx);
-
/**
* aio_context_set_poll_params:
* @ctx: the aio context
diff --git a/tests/unit/test-nested-aio-poll.c b/tests/unit/test-nested-aio-poll.c
index 45484e745b..d13ecccd8c 100644
--- a/tests/unit/test-nested-aio-poll.c
+++ b/tests/unit/test-nested-aio-poll.c
@@ -83,12 +83,6 @@ static void test(void)
/* Enable polling */
aio_context_set_poll_params(td.ctx, 1000000, 2, 2, &error_abort);
- /*
- * The GSource is unused but this has the side-effect of changing the fdmon
- * that AioContext uses.
- */
- aio_get_g_source(td.ctx);
-
/* Make the event notifier active (set) right away */
event_notifier_init(&td.poll_notifier, 1);
aio_set_event_notifier(td.ctx, &td.poll_notifier,
diff --git a/util/aio-posix.c b/util/aio-posix.c
index 9de05ee7e8..bebd9ce3a2 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -743,18 +743,6 @@ void aio_context_destroy(AioContext *ctx)
aio_free_deleted_handlers(ctx);
}
-void aio_context_use_g_source(AioContext *ctx)
-{
- /*
- * Disable io_uring when the glib main loop is used because it doesn't
- * support mixed glib/aio_poll() usage. It relies on aio_poll() being
- * called regularly so that changes to the monitored file descriptors are
- * submitted, otherwise a list of pending fd handlers builds up.
- */
- fdmon_io_uring_destroy(ctx);
- aio_free_deleted_handlers(ctx);
-}
-
void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
int64_t grow, int64_t shrink, Error **errp)
{
diff --git a/util/aio-win32.c b/util/aio-win32.c
index 6583d5c5f3..34c4074133 100644
--- a/util/aio-win32.c
+++ b/util/aio-win32.c
@@ -427,10 +427,6 @@ void aio_context_destroy(AioContext *ctx)
{
}
-void aio_context_use_g_source(AioContext *ctx)
-{
-}
-
void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
int64_t grow, int64_t shrink, Error **errp)
{
diff --git a/util/async.c b/util/async.c
index 2719c629ae..a39410d675 100644
--- a/util/async.c
+++ b/util/async.c
@@ -430,7 +430,6 @@ static GSourceFuncs aio_source_funcs = {
GSource *aio_get_g_source(AioContext *ctx)
{
- aio_context_use_g_source(ctx);
g_source_ref(&ctx->source);
return &ctx->source;
}
--
2.51.0
^ permalink raw reply related [flat|nested] 25+ messages in thread* Re: [PATCH v4 05/12] aio: remove aio_context_use_g_source()
2025-09-10 17:56 ` [PATCH v4 05/12] aio: remove aio_context_use_g_source() Stefan Hajnoczi
@ 2025-10-09 15:46 ` Kevin Wolf
2025-10-09 16:59 ` Kevin Wolf
0 siblings, 1 reply; 25+ messages in thread
From: Kevin Wolf @ 2025-10-09 15:46 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Aarushi Mehta, Fam Zheng, Stefano Garzarella,
Hanna Czenczek, eblake, qemu-block, hibriansong, Stefan Weil,
Paolo Bonzini
Am 10.09.2025 um 19:56 hat Stefan Hajnoczi geschrieben:
> There is no need for aio_context_use_g_source() now that epoll(7) and
> io_uring(7) file descriptor monitoring works with the glib event loop.
> AioContext doesn't need to be notified that GSource is being used.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
We should probably mention in the commit message that this causes the
default fdmon on Linux to change from poll to io_uring. It's a small
code change, but it makes QEMU use a completely different code path by
default.
With this added: Reviewed-by: Kevin Wolf <kwolf@redhat.com>
> diff --git a/tests/unit/test-nested-aio-poll.c b/tests/unit/test-nested-aio-poll.c
> index 45484e745b..d13ecccd8c 100644
> --- a/tests/unit/test-nested-aio-poll.c
> +++ b/tests/unit/test-nested-aio-poll.c
> @@ -83,12 +83,6 @@ static void test(void)
> /* Enable polling */
> aio_context_set_poll_params(td.ctx, 1000000, 2, 2, &error_abort);
>
> - /*
> - * The GSource is unused but this has the side-effect of changing the fdmon
> - * that AioContext uses.
> - */
> - aio_get_g_source(td.ctx);
> -
> /* Make the event notifier active (set) right away */
> event_notifier_init(&td.poll_notifier, 1);
> aio_set_event_notifier(td.ctx, &td.poll_notifier,
I wonder if it wouldn't make sense to squash this hunk into patch 3
('tests/unit: skip test-nested-aio-poll with io_uring').
Kevin
^ permalink raw reply [flat|nested] 25+ messages in thread* Re: [PATCH v4 05/12] aio: remove aio_context_use_g_source()
2025-10-09 15:46 ` Kevin Wolf
@ 2025-10-09 16:59 ` Kevin Wolf
0 siblings, 0 replies; 25+ messages in thread
From: Kevin Wolf @ 2025-10-09 16:59 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Aarushi Mehta, Fam Zheng, Stefano Garzarella,
Hanna Czenczek, eblake, qemu-block, hibriansong, Stefan Weil,
Paolo Bonzini
Am 09.10.2025 um 17:46 hat Kevin Wolf geschrieben:
> Am 10.09.2025 um 19:56 hat Stefan Hajnoczi geschrieben:
> > There is no need for aio_context_use_g_source() now that epoll(7) and
> > io_uring(7) file descriptor monitoring works with the glib event loop.
> > AioContext doesn't need to be notified that GSource is being used.
> >
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > Reviewed-by: Eric Blake <eblake@redhat.com>
>
> We should probably mention in the commit message that this causes the
> default fdmon on Linux to change from poll to io_uring. It's a small
> code change, but it makes QEMU use a completely different code path by
> default.
Just to make sure, I ran 'make check' after this patch and it's failing
for me:
10/401 qemu:qtest+qtest-x86_64 / qtest-x86_64/ahci-test TIMEOUT 150.02s killed by signal 15 SIGTERM
133/401 qemu:unit / test-aio TIMEOUT 30.01s killed by signal 15 SIGTERM
137/401 qemu:unit / test-bdrv-drain TIMEOUT 30.01s killed by signal 15 SIGTERM
142/401 qemu:unit / test-block-iothread TIMEOUT 30.01s killed by signal 15 SIGTERM
192/401 qemu:doc+rust / rust-bql-rs-doctests FAIL 0.84s exit status 101
311/401 qemu:block / io-qcow2-267 ERROR 3.20s exit status 1
321/401 qemu:block / io-qcow2-copy-before-write TIMEOUT 180.01s killed by signal 15 SIGTERM
Some of them look unrelated, but I have confirmed that the three unit
tests still pass before this patch (and still hang after the complete
series).
Kevin
^ permalink raw reply [flat|nested] 25+ messages in thread
* [PATCH v4 06/12] aio: free AioContext when aio_context_new() fails
2025-09-10 17:56 [PATCH v4 00/12] aio: add the aio_add_sqe() io_uring API Stefan Hajnoczi
` (4 preceding siblings ...)
2025-09-10 17:56 ` [PATCH v4 05/12] aio: remove aio_context_use_g_source() Stefan Hajnoczi
@ 2025-09-10 17:56 ` Stefan Hajnoczi
2025-10-09 16:06 ` Kevin Wolf
2025-09-10 17:56 ` [PATCH v4 07/12] aio: add errp argument to aio_context_setup() Stefan Hajnoczi
` (5 subsequent siblings)
11 siblings, 1 reply; 25+ messages in thread
From: Stefan Hajnoczi @ 2025-09-10 17:56 UTC (permalink / raw)
To: qemu-devel
Cc: Aarushi Mehta, Fam Zheng, Stefano Garzarella, Hanna Czenczek,
eblake, Stefan Hajnoczi, Kevin Wolf, qemu-block, hibriansong,
Stefan Weil, Paolo Bonzini
g_source_destroy() only removes the GSource from the GMainContext it's
attached to, if any. It does not free it.
Use g_source_unref() instead so that the AioContext (which embeds a
GSource) is freed. There is no need to call g_source_destroy() in
aio_context_new() because the GSource isn't attached to a GMainContext
yet.
aio_ctx_finalize() expects everything to be set up already, so introduce
the new ctx->initialized boolean and do nothing when called with
!initialized. This also requires moving aio_context_setup() down after
event_notifier_init() since aio_ctx_finalize() won't release any
resources that aio_context_setup() acquired.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
v2:
- Fix spacing in aio_ctx_finalize() argument list [Eric]
---
include/block/aio.h | 3 +++
util/async.c | 14 +++++++++++---
2 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/include/block/aio.h b/include/block/aio.h
index 1657740a0e..2760f308f5 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -291,6 +291,9 @@ struct AioContext {
gpointer epollfd_tag;
const FDMonOps *fdmon_ops;
+
+ /* Was aio_context_new() successful? */
+ bool initialized;
};
/**
diff --git a/util/async.c b/util/async.c
index a39410d675..34aaab4e9e 100644
--- a/util/async.c
+++ b/util/async.c
@@ -363,12 +363,16 @@ aio_ctx_dispatch(GSource *source,
}
static void
-aio_ctx_finalize(GSource *source)
+aio_ctx_finalize(GSource *source)
{
AioContext *ctx = (AioContext *) source;
QEMUBH *bh;
unsigned flags;
+ if (!ctx->initialized) {
+ return;
+ }
+
thread_pool_free_aio(ctx->thread_pool);
#ifdef CONFIG_LINUX_AIO
@@ -579,13 +583,15 @@ AioContext *aio_context_new(Error **errp)
ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
QSLIST_INIT(&ctx->bh_list);
QSIMPLEQ_INIT(&ctx->bh_slice_list);
- aio_context_setup(ctx);
ret = event_notifier_init(&ctx->notifier, false);
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to initialize event notifier");
goto fail;
}
+
+ aio_context_setup(ctx);
+
g_source_set_can_recurse(&ctx->source, true);
qemu_lockcnt_init(&ctx->list_lock);
@@ -619,9 +625,11 @@ AioContext *aio_context_new(Error **errp)
register_aiocontext(ctx);
+ ctx->initialized = true;
+
return ctx;
fail:
- g_source_destroy(&ctx->source);
+ g_source_unref(&ctx->source);
return NULL;
}
--
2.51.0
^ permalink raw reply related [flat|nested] 25+ messages in thread* Re: [PATCH v4 06/12] aio: free AioContext when aio_context_new() fails
2025-09-10 17:56 ` [PATCH v4 06/12] aio: free AioContext when aio_context_new() fails Stefan Hajnoczi
@ 2025-10-09 16:06 ` Kevin Wolf
0 siblings, 0 replies; 25+ messages in thread
From: Kevin Wolf @ 2025-10-09 16:06 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Aarushi Mehta, Fam Zheng, Stefano Garzarella,
Hanna Czenczek, eblake, qemu-block, hibriansong, Stefan Weil,
Paolo Bonzini
Am 10.09.2025 um 19:56 hat Stefan Hajnoczi geschrieben:
> g_source_destroy() only removes the GSource from the GMainContext it's
> attached to, if any. It does not free it.
>
> Use g_source_unref() instead so that the AioContext (which embeds a
> GSource) is freed. There is no need to call g_source_destroy() in
> aio_context_new() because the GSource isn't attached to a GMainContext
> yet.
>
> aio_ctx_finalize() expects everything to be set up already, so introduce
> the new ctx->initialized boolean and do nothing when called with
> !initialized. This also requires moving aio_context_setup() down after
> event_notifier_init() since aio_ctx_finalize() won't release any
> resources that aio_context_setup() acquired.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
> v2:
> - Fix spacing in aio_ctx_finalize() argument list [Eric]
> ---
> include/block/aio.h | 3 +++
> util/async.c | 14 +++++++++++---
> 2 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/include/block/aio.h b/include/block/aio.h
> index 1657740a0e..2760f308f5 100644
> --- a/include/block/aio.h
> +++ b/include/block/aio.h
> @@ -291,6 +291,9 @@ struct AioContext {
> gpointer epollfd_tag;
>
> const FDMonOps *fdmon_ops;
> +
> + /* Was aio_context_new() successful? */
> + bool initialized;
> };
>
> /**
> diff --git a/util/async.c b/util/async.c
> index a39410d675..34aaab4e9e 100644
> --- a/util/async.c
> +++ b/util/async.c
> @@ -363,12 +363,16 @@ aio_ctx_dispatch(GSource *source,
> }
>
> static void
> -aio_ctx_finalize(GSource *source)
> +aio_ctx_finalize(GSource *source)
> {
> AioContext *ctx = (AioContext *) source;
> QEMUBH *bh;
> unsigned flags;
>
> + if (!ctx->initialized) {
> + return;
> + }
You had to move aio_context_setup() down in aio_context_new() to make
sure that this doesn't leak things.
How will we make sure that nobody adds another error path after
allocating something after g_source_new()? g_source_new() doesn't seem
to guarantee that AioContext starts zeroed, which is annoying if we
wanted to just make aio_ctx_finalize() safe to be called from before the
first error path.
> thread_pool_free_aio(ctx->thread_pool);
>
> #ifdef CONFIG_LINUX_AIO
> @@ -579,13 +583,15 @@ AioContext *aio_context_new(Error **errp)
> ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
> QSLIST_INIT(&ctx->bh_list);
> QSIMPLEQ_INIT(&ctx->bh_slice_list);
> - aio_context_setup(ctx);
>
> ret = event_notifier_init(&ctx->notifier, false);
> if (ret < 0) {
> error_setg_errno(errp, -ret, "Failed to initialize event notifier");
> goto fail;
> }
>
> +
> + aio_context_setup(ctx);
Can we at least add a comment here saying that there must be no error
after this aio_context_setup() call any more because we would then leak
things?
> g_source_set_can_recurse(&ctx->source, true);
> qemu_lockcnt_init(&ctx->list_lock);
>
> @@ -619,9 +625,11 @@ AioContext *aio_context_new(Error **errp)
>
> register_aiocontext(ctx);
>
> + ctx->initialized = true;
> +
> return ctx;
> fail:
> - g_source_destroy(&ctx->source);
> + g_source_unref(&ctx->source);
> return NULL;
> }
Kevin
^ permalink raw reply [flat|nested] 25+ messages in thread
* [PATCH v4 07/12] aio: add errp argument to aio_context_setup()
2025-09-10 17:56 [PATCH v4 00/12] aio: add the aio_add_sqe() io_uring API Stefan Hajnoczi
` (5 preceding siblings ...)
2025-09-10 17:56 ` [PATCH v4 06/12] aio: free AioContext when aio_context_new() fails Stefan Hajnoczi
@ 2025-09-10 17:56 ` Stefan Hajnoczi
2025-10-09 16:16 ` Kevin Wolf
2025-09-10 17:56 ` [PATCH v4 08/12] aio-posix: gracefully handle io_uring_queue_init() failure Stefan Hajnoczi
` (4 subsequent siblings)
11 siblings, 1 reply; 25+ messages in thread
From: Stefan Hajnoczi @ 2025-09-10 17:56 UTC (permalink / raw)
To: qemu-devel
Cc: Aarushi Mehta, Fam Zheng, Stefano Garzarella, Hanna Czenczek,
eblake, Stefan Hajnoczi, Kevin Wolf, qemu-block, hibriansong,
Stefan Weil, Paolo Bonzini
When aio_context_new() -> aio_context_setup() fails at startup it
doesn't really matter whether errors are returned to the caller or the
process terminates immediately.
However, it is not acceptable to terminate when hotplugging --object
iothread at runtime. Refactor aio_context_setup() so that errors can be
propagated. The next commit will set errp when fdmon_io_uring_setup()
fails.
Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
include/block/aio.h | 3 ++-
util/aio-posix.c | 2 +-
util/aio-win32.c | 2 +-
util/async.c | 7 ++++++-
4 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/include/block/aio.h b/include/block/aio.h
index 2760f308f5..d919d7c8f4 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -718,10 +718,11 @@ void qemu_set_current_aio_context(AioContext *ctx);
/**
* aio_context_setup:
* @ctx: the aio context
+ * @errp: error pointer
*
* Initialize the aio context.
*/
-void aio_context_setup(AioContext *ctx);
+void aio_context_setup(AioContext *ctx, Error **errp);
/**
* aio_context_destroy:
diff --git a/util/aio-posix.c b/util/aio-posix.c
index bebd9ce3a2..bbe470c145 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -718,7 +718,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
return progress;
}
-void aio_context_setup(AioContext *ctx)
+void aio_context_setup(AioContext *ctx, Error **errp)
{
ctx->fdmon_ops = &fdmon_poll_ops;
ctx->epollfd = -1;
diff --git a/util/aio-win32.c b/util/aio-win32.c
index 34c4074133..4ba401ff92 100644
--- a/util/aio-win32.c
+++ b/util/aio-win32.c
@@ -419,7 +419,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
return progress;
}
-void aio_context_setup(AioContext *ctx)
+void aio_context_setup(AioContext *ctx, Error **errp)
{
}
diff --git a/util/async.c b/util/async.c
index 34aaab4e9e..2bb7e1f3c1 100644
--- a/util/async.c
+++ b/util/async.c
@@ -577,6 +577,7 @@ static void co_schedule_bh_cb(void *opaque)
AioContext *aio_context_new(Error **errp)
{
+ ERRP_GUARD();
int ret;
AioContext *ctx;
@@ -590,7 +591,11 @@ AioContext *aio_context_new(Error **errp)
goto fail;
}
- aio_context_setup(ctx);
+ aio_context_setup(ctx, errp);
+ if (*errp) {
+ event_notifier_cleanup(&ctx->notifier);
+ goto fail;
+ }
g_source_set_can_recurse(&ctx->source, true);
qemu_lockcnt_init(&ctx->list_lock);
--
2.51.0
^ permalink raw reply related [flat|nested] 25+ messages in thread* Re: [PATCH v4 07/12] aio: add errp argument to aio_context_setup()
2025-09-10 17:56 ` [PATCH v4 07/12] aio: add errp argument to aio_context_setup() Stefan Hajnoczi
@ 2025-10-09 16:16 ` Kevin Wolf
0 siblings, 0 replies; 25+ messages in thread
From: Kevin Wolf @ 2025-10-09 16:16 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Aarushi Mehta, Fam Zheng, Stefano Garzarella,
Hanna Czenczek, eblake, qemu-block, hibriansong, Stefan Weil,
Paolo Bonzini
Am 10.09.2025 um 19:56 hat Stefan Hajnoczi geschrieben:
> When aio_context_new() -> aio_context_setup() fails at startup it
> doesn't really matter whether errors are returned to the caller or the
> process terminates immediately.
>
> However, it is not acceptable to terminate when hotplugging --object
> iothread at runtime. Refactor aio_context_setup() so that errors can be
> propagated. The next commit will set errp when fdmon_io_uring_setup()
> fails.
>
> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> diff --git a/include/block/aio.h b/include/block/aio.h
> index 2760f308f5..d919d7c8f4 100644
> --- a/include/block/aio.h
> +++ b/include/block/aio.h
> @@ -718,10 +718,11 @@ void qemu_set_current_aio_context(AioContext *ctx);
> /**
> * aio_context_setup:
> * @ctx: the aio context
> + * @errp: error pointer
> *
> * Initialize the aio context.
> */
> -void aio_context_setup(AioContext *ctx);
> +void aio_context_setup(AioContext *ctx, Error **errp);
I don't really mind much, but the convention these days is that
functions don't only take an Error **, but also return a bool or
0/-errno.
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
^ permalink raw reply [flat|nested] 25+ messages in thread
* [PATCH v4 08/12] aio-posix: gracefully handle io_uring_queue_init() failure
2025-09-10 17:56 [PATCH v4 00/12] aio: add the aio_add_sqe() io_uring API Stefan Hajnoczi
` (6 preceding siblings ...)
2025-09-10 17:56 ` [PATCH v4 07/12] aio: add errp argument to aio_context_setup() Stefan Hajnoczi
@ 2025-09-10 17:56 ` Stefan Hajnoczi
2025-10-09 16:19 ` Kevin Wolf
2025-09-10 17:57 ` [PATCH v4 09/12] aio-posix: add aio_add_sqe() API for user-defined io_uring requests Stefan Hajnoczi
` (3 subsequent siblings)
11 siblings, 1 reply; 25+ messages in thread
From: Stefan Hajnoczi @ 2025-09-10 17:56 UTC (permalink / raw)
To: qemu-devel
Cc: Aarushi Mehta, Fam Zheng, Stefano Garzarella, Hanna Czenczek,
eblake, Stefan Hajnoczi, Kevin Wolf, qemu-block, hibriansong,
Stefan Weil, Paolo Bonzini
io_uring may not be available at runtime due to system policies (e.g.
the io_uring_disabled sysctl) or creation could fail due to file
descriptor resource limits.
Handle failure scenarios as follows:
If another AioContext already has io_uring, then fail AioContext
creation so that the aio_add_sqe() API is available uniformly from all
QEMU threads. Otherwise fall back to epoll(7) if io_uring is
unavailable.
Notes:
- Update the comment about selecting the fastest fdmon implementation.
At this point it's not about speed anymore, it's about aio_add_sqe()
API availability.
- Uppercase the error message when converting from error_report() to
error_setg_errno() for consistency (but there are instances of
lowercase in the codebase).
- It's easier to move the #ifdefs from aio-posix.h to aio-posix.c.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
util/aio-posix.h | 12 ++----------
util/aio-posix.c | 29 ++++++++++++++++++++++++++---
util/fdmon-io_uring.c | 8 ++++----
3 files changed, 32 insertions(+), 17 deletions(-)
diff --git a/util/aio-posix.h b/util/aio-posix.h
index f9994ed79e..6f9d97d866 100644
--- a/util/aio-posix.h
+++ b/util/aio-posix.h
@@ -18,6 +18,7 @@
#define AIO_POSIX_H
#include "block/aio.h"
+#include "qapi/error.h"
struct AioHandler {
GPollFD pfd;
@@ -72,17 +73,8 @@ static inline void fdmon_epoll_disable(AioContext *ctx)
#endif /* !CONFIG_EPOLL_CREATE1 */
#ifdef CONFIG_LINUX_IO_URING
-bool fdmon_io_uring_setup(AioContext *ctx);
+void fdmon_io_uring_setup(AioContext *ctx, Error **errp);
void fdmon_io_uring_destroy(AioContext *ctx);
-#else
-static inline bool fdmon_io_uring_setup(AioContext *ctx)
-{
- return false;
-}
-
-static inline void fdmon_io_uring_destroy(AioContext *ctx)
-{
-}
#endif /* !CONFIG_LINUX_IO_URING */
#endif /* AIO_POSIX_H */
diff --git a/util/aio-posix.c b/util/aio-posix.c
index bbe470c145..800b4debbf 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -16,6 +16,7 @@
#include "qemu/osdep.h"
#include "block/block.h"
#include "block/thread-pool.h"
+#include "qapi/error.h"
#include "qemu/main-loop.h"
#include "qemu/lockcnt.h"
#include "qemu/rcu.h"
@@ -724,17 +725,39 @@ void aio_context_setup(AioContext *ctx, Error **errp)
ctx->epollfd = -1;
ctx->epollfd_tag = NULL;
- /* Use the fastest fd monitoring implementation if available */
- if (fdmon_io_uring_setup(ctx)) {
- return;
+#ifdef CONFIG_LINUX_IO_URING
+ {
+ static bool need_io_uring;
+ Error *local_err = NULL; /* ERRP_GUARD() doesn't handle error_abort */
+
+ /* io_uring takes precedence because it provides aio_add_sqe() support */
+ fdmon_io_uring_setup(ctx, &local_err);
+ if (!local_err) {
+ /*
+ * If one AioContext gets io_uring, then all AioContexts need io_uring
+ * so that aio_add_sqe() support is available across all threads.
+ */
+ need_io_uring = true;
+ return;
+ }
+ if (need_io_uring) {
+ error_propagate(errp, local_err);
+ return;
+ }
+
+ /* Silently fall back on systems where io_uring is unavailable */
+ error_free(local_err);
}
+#endif /* CONFIG_LINUX_IO_URING */
fdmon_epoll_setup(ctx);
}
void aio_context_destroy(AioContext *ctx)
{
+#ifdef CONFIG_LINUX_IO_URING
fdmon_io_uring_destroy(ctx);
+#endif
qemu_lockcnt_lock(&ctx->list_lock);
fdmon_epoll_disable(ctx);
diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c
index 4b6dc8903f..3181601767 100644
--- a/util/fdmon-io_uring.c
+++ b/util/fdmon-io_uring.c
@@ -45,6 +45,7 @@
#include "qemu/osdep.h"
#include <poll.h>
+#include "qapi/error.h"
#include "qemu/rcu_queue.h"
#include "aio-posix.h"
@@ -369,7 +370,7 @@ static const FDMonOps fdmon_io_uring_ops = {
.gsource_dispatch = fdmon_io_uring_gsource_dispatch,
};
-bool fdmon_io_uring_setup(AioContext *ctx)
+void fdmon_io_uring_setup(AioContext *ctx, Error **errp)
{
int ret;
@@ -377,15 +378,14 @@ bool fdmon_io_uring_setup(AioContext *ctx)
ret = io_uring_queue_init(FDMON_IO_URING_ENTRIES, &ctx->fdmon_io_uring, 0);
if (ret != 0) {
- return false;
+ error_setg_errno(errp, -ret, "Failed to initialize io_uring");
+ return;
}
QSLIST_INIT(&ctx->submit_list);
ctx->fdmon_ops = &fdmon_io_uring_ops;
ctx->io_uring_fd_tag = g_source_add_unix_fd(&ctx->source,
ctx->fdmon_io_uring.ring_fd, G_IO_IN);
-
- return true;
}
void fdmon_io_uring_destroy(AioContext *ctx)
--
2.51.0
^ permalink raw reply related [flat|nested] 25+ messages in thread* Re: [PATCH v4 08/12] aio-posix: gracefully handle io_uring_queue_init() failure
2025-09-10 17:56 ` [PATCH v4 08/12] aio-posix: gracefully handle io_uring_queue_init() failure Stefan Hajnoczi
@ 2025-10-09 16:19 ` Kevin Wolf
0 siblings, 0 replies; 25+ messages in thread
From: Kevin Wolf @ 2025-10-09 16:19 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Aarushi Mehta, Fam Zheng, Stefano Garzarella,
Hanna Czenczek, eblake, qemu-block, hibriansong, Stefan Weil,
Paolo Bonzini
Am 10.09.2025 um 19:56 hat Stefan Hajnoczi geschrieben:
> io_uring may not be available at runtime due to system policies (e.g.
> the io_uring_disabled sysctl) or creation could fail due to file
> descriptor resource limits.
>
> Handle failure scenarios as follows:
>
> If another AioContext already has io_uring, then fail AioContext
> creation so that the aio_add_sqe() API is available uniformly from all
> QEMU threads. Otherwise fall back to epoll(7) if io_uring is
> unavailable.
>
> Notes:
> - Update the comment about selecting the fastest fdmon implementation.
> At this point it's not about speed anymore, it's about aio_add_sqe()
> API availability.
> - Uppercase the error message when converting from error_report() to
> error_setg_errno() for consistency (but there are instances of
> lowercase in the codebase).
> - It's easier to move the #ifdefs from aio-posix.h to aio-posix.c.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> @@ -369,7 +370,7 @@ static const FDMonOps fdmon_io_uring_ops = {
> .gsource_dispatch = fdmon_io_uring_gsource_dispatch,
> };
>
> -bool fdmon_io_uring_setup(AioContext *ctx)
> +void fdmon_io_uring_setup(AioContext *ctx, Error **errp)
> {
> int ret;
Same as in the previous patch, it would be more conventional to keep the
bool return code in addition to the Error **. Either way:
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
^ permalink raw reply [flat|nested] 25+ messages in thread
* [PATCH v4 09/12] aio-posix: add aio_add_sqe() API for user-defined io_uring requests
2025-09-10 17:56 [PATCH v4 00/12] aio: add the aio_add_sqe() io_uring API Stefan Hajnoczi
` (7 preceding siblings ...)
2025-09-10 17:56 ` [PATCH v4 08/12] aio-posix: gracefully handle io_uring_queue_init() failure Stefan Hajnoczi
@ 2025-09-10 17:57 ` Stefan Hajnoczi
2025-10-10 15:23 ` Kevin Wolf
2025-09-10 17:57 ` [PATCH v4 10/12] aio-posix: avoid EventNotifier for cqe_handler_bh Stefan Hajnoczi
` (2 subsequent siblings)
11 siblings, 1 reply; 25+ messages in thread
From: Stefan Hajnoczi @ 2025-09-10 17:57 UTC (permalink / raw)
To: qemu-devel
Cc: Aarushi Mehta, Fam Zheng, Stefano Garzarella, Hanna Czenczek,
eblake, Stefan Hajnoczi, Kevin Wolf, qemu-block, hibriansong,
Stefan Weil, Paolo Bonzini
Introduce the aio_add_sqe() API for submitting io_uring requests in the
current AioContext. This allows other components in QEMU, like the block
layer, to take advantage of io_uring features without creating their own
io_uring context.
This API supports nested event loops just like file descriptor
monitoring and BHs do. This comes at a complexity cost: a BH is required
to dispatch CQE callbacks and they are placed on a list so that a nested
event loop can invoke its parent's pending CQE callbacks. If you're
wondering why CqeHandler exists instead of just a callback function
pointer, this is why.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
v2:
- Fix pre_sqe -> prep_sqe typo [Eric]
- Add #endif terminator comment [Eric]
---
include/block/aio.h | 84 ++++++++++++++++++++++-
util/aio-posix.h | 1 +
util/aio-posix.c | 9 +++
util/fdmon-io_uring.c | 152 ++++++++++++++++++++++++++++++++----------
4 files changed, 208 insertions(+), 38 deletions(-)
diff --git a/include/block/aio.h b/include/block/aio.h
index d919d7c8f4..56ea0d47b7 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -61,6 +61,27 @@ typedef struct LuringState LuringState;
/* Is polling disabled? */
bool aio_poll_disabled(AioContext *ctx);
+#ifdef CONFIG_LINUX_IO_URING
+/*
+ * Each io_uring request must have a unique CqeHandler that processes the cqe.
+ * The lifetime of a CqeHandler must be at least from aio_add_sqe() until
+ * ->cb() invocation.
+ */
+typedef struct CqeHandler CqeHandler;
+struct CqeHandler {
+ /* Called by the AioContext when the request has completed */
+ void (*cb)(CqeHandler *handler);
+
+ /* Used internally, do not access this */
+ QSIMPLEQ_ENTRY(CqeHandler) next;
+
+ /* This field is filled in before ->cb() is called */
+ struct io_uring_cqe cqe;
+};
+
+typedef QSIMPLEQ_HEAD(, CqeHandler) CqeHandlerSimpleQ;
+#endif /* CONFIG_LINUX_IO_URING */
+
/* Callbacks for file descriptor monitoring implementations */
typedef struct {
/*
@@ -138,6 +159,27 @@ typedef struct {
* Called with list_lock incremented.
*/
void (*gsource_dispatch)(AioContext *ctx, AioHandlerList *ready_list);
+
+#ifdef CONFIG_LINUX_IO_URING
+ /**
+ * aio_add_sqe: Add an io_uring sqe for submission.
+ * @prep_sqe: invoked with an sqe that should be prepared for submission
+ * @opaque: user-defined argument to @prep_sqe()
+ * @cqe_handler: the unique cqe handler associated with this request
+ *
+ * The caller's @prep_sqe() function is invoked to fill in the details of
+ * the sqe. Do not call io_uring_sqe_set_data() on this sqe.
+ *
+ * The kernel may see the sqe as soon as @prep_sqe() returns or it may take
+ * until the next event loop iteration.
+ *
+ * This function is called from the current AioContext and is not
+ * thread-safe.
+ */
+ void (*add_sqe)(AioContext *ctx,
+ void (*prep_sqe)(struct io_uring_sqe *sqe, void *opaque),
+ void *opaque, CqeHandler *cqe_handler);
+#endif /* CONFIG_LINUX_IO_URING */
} FDMonOps;
/*
@@ -255,7 +297,11 @@ struct AioContext {
struct io_uring fdmon_io_uring;
AioHandlerSList submit_list;
gpointer io_uring_fd_tag;
-#endif
+
+ /* Pending callback state for cqe handlers */
+ CqeHandlerSimpleQ cqe_handler_ready_list;
+ QEMUBH *cqe_handler_bh;
+#endif /* CONFIG_LINUX_IO_URING */
/* TimerLists for calling timers - one per clock type. Has its own
* locking.
@@ -761,4 +807,40 @@ void aio_context_set_aio_params(AioContext *ctx, int64_t max_batch);
*/
void aio_context_set_thread_pool_params(AioContext *ctx, int64_t min,
int64_t max, Error **errp);
+
+#ifdef CONFIG_LINUX_IO_URING
+/**
+ * aio_has_io_uring: Return whether io_uring is available.
+ *
+ * io_uring is either available in all AioContexts or in none, so this only
+ * needs to be called once from within any thread's AioContext.
+ */
+static inline bool aio_has_io_uring(void)
+{
+ AioContext *ctx = qemu_get_current_aio_context();
+ return ctx->fdmon_ops->add_sqe;
+}
+
+/**
+ * aio_add_sqe: Add an io_uring sqe for submission.
+ * @prep_sqe: invoked with an sqe that should be prepared for submission
+ * @opaque: user-defined argument to @prep_sqe()
+ * @cqe_handler: the unique cqe handler associated with this request
+ *
+ * The caller's @prep_sqe() function is invoked to fill in the details of the
+ * sqe. Do not call io_uring_sqe_set_data() on this sqe.
+ *
+ * The sqe is submitted by the current AioContext. The kernel may see the sqe
+ * as soon as @prep_sqe() returns or it may take until the next event loop
+ * iteration.
+ *
+ * When the AioContext is destroyed, pending sqes are ignored and their
+ * CqeHandlers are not invoked.
+ *
+ * This function must be called only when aio_has_io_uring() returns true.
+ */
+void aio_add_sqe(void (*prep_sqe)(struct io_uring_sqe *sqe, void *opaque),
+ void *opaque, CqeHandler *cqe_handler);
+#endif /* CONFIG_LINUX_IO_URING */
+
#endif
diff --git a/util/aio-posix.h b/util/aio-posix.h
index 6f9d97d866..57ef801a5f 100644
--- a/util/aio-posix.h
+++ b/util/aio-posix.h
@@ -36,6 +36,7 @@ struct AioHandler {
#ifdef CONFIG_LINUX_IO_URING
QSLIST_ENTRY(AioHandler) node_submitted;
unsigned flags; /* see fdmon-io_uring.c */
+ CqeHandler cqe_handler;
#endif
int64_t poll_idle_timeout; /* when to stop userspace polling */
bool poll_ready; /* has polling detected an event? */
diff --git a/util/aio-posix.c b/util/aio-posix.c
index 800b4debbf..df945312b3 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -797,3 +797,12 @@ void aio_context_set_aio_params(AioContext *ctx, int64_t max_batch)
aio_notify(ctx);
}
+
+#ifdef CONFIG_LINUX_IO_URING
+void aio_add_sqe(void (*prep_sqe)(struct io_uring_sqe *sqe, void *opaque),
+ void *opaque, CqeHandler *cqe_handler)
+{
+ AioContext *ctx = qemu_get_current_aio_context();
+ ctx->fdmon_ops->add_sqe(ctx, prep_sqe, opaque, cqe_handler);
+}
+#endif /* CONFIG_LINUX_IO_URING */
diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c
index 3181601767..7f7c50907d 100644
--- a/util/fdmon-io_uring.c
+++ b/util/fdmon-io_uring.c
@@ -46,6 +46,7 @@
#include "qemu/osdep.h"
#include <poll.h>
#include "qapi/error.h"
+#include "qemu/defer-call.h"
#include "qemu/rcu_queue.h"
#include "aio-posix.h"
@@ -76,8 +77,8 @@ static inline int pfd_events_from_poll(int poll_events)
}
/*
- * Returns an sqe for submitting a request. Only be called within
- * fdmon_io_uring_wait().
+ * Returns an sqe for submitting a request. Only called from the AioContext
+ * thread.
*/
static struct io_uring_sqe *get_sqe(AioContext *ctx)
{
@@ -168,23 +169,43 @@ static void fdmon_io_uring_update(AioContext *ctx,
}
}
+static void fdmon_io_uring_add_sqe(AioContext *ctx,
+ void (*prep_sqe)(struct io_uring_sqe *sqe, void *opaque),
+ void *opaque, CqeHandler *cqe_handler)
+{
+ struct io_uring_sqe *sqe = get_sqe(ctx);
+
+ prep_sqe(sqe, opaque);
+ io_uring_sqe_set_data(sqe, cqe_handler);
+}
+
+static void fdmon_special_cqe_handler(CqeHandler *cqe_handler)
+{
+ /*
+ * This is an empty function that is never called. It is used as a function
+ * pointer to distinguish it from ordinary cqe handlers.
+ */
+}
+
static void add_poll_add_sqe(AioContext *ctx, AioHandler *node)
{
struct io_uring_sqe *sqe = get_sqe(ctx);
int events = poll_events_from_pfd(node->pfd.events);
io_uring_prep_poll_add(sqe, node->pfd.fd, events);
- io_uring_sqe_set_data(sqe, node);
+ node->cqe_handler.cb = fdmon_special_cqe_handler;
+ io_uring_sqe_set_data(sqe, &node->cqe_handler);
}
static void add_poll_remove_sqe(AioContext *ctx, AioHandler *node)
{
struct io_uring_sqe *sqe = get_sqe(ctx);
+ CqeHandler *cqe_handler = &node->cqe_handler;
#ifdef LIBURING_HAVE_DATA64
- io_uring_prep_poll_remove(sqe, (uintptr_t)node);
+ io_uring_prep_poll_remove(sqe, (uintptr_t)cqe_handler);
#else
- io_uring_prep_poll_remove(sqe, node);
+ io_uring_prep_poll_remove(sqe, cqe_handler);
#endif
io_uring_sqe_set_data(sqe, NULL);
}
@@ -233,19 +254,13 @@ static void fill_sq_ring(AioContext *ctx)
}
}
-/* Returns true if a handler became ready */
-static bool process_cqe(AioContext *ctx,
- AioHandlerList *ready_list,
- struct io_uring_cqe *cqe)
+static bool process_cqe_aio_handler(AioContext *ctx,
+ AioHandlerList *ready_list,
+ AioHandler *node,
+ struct io_uring_cqe *cqe)
{
- AioHandler *node = io_uring_cqe_get_data(cqe);
unsigned flags;
- /* poll_timeout and poll_remove have a zero user_data field */
- if (!node) {
- return false;
- }
-
/*
* Deletion can only happen when IORING_OP_POLL_ADD completes. If we race
* with enqueue() here then we can safely clear the FDMON_IO_URING_REMOVE
@@ -269,6 +284,61 @@ static bool process_cqe(AioContext *ctx,
return true;
}
+/* Process CqeHandlers from the ready list */
+static void cqe_handler_bh(void *opaque)
+{
+ AioContext *ctx = opaque;
+ CqeHandlerSimpleQ *ready_list = &ctx->cqe_handler_ready_list;
+
+ /*
+ * If cqe_handler->cb() calls aio_poll() it must continue processing
+ * ready_list. Schedule a BH so the inner event loop calls us again.
+ */
+ qemu_bh_schedule(ctx->cqe_handler_bh);
+
+ /* Handlers may use defer_call() to coalesce frequent operations */
+ defer_call_begin();
+
+ while (!QSIMPLEQ_EMPTY(ready_list)) {
+ CqeHandler *cqe_handler = QSIMPLEQ_FIRST(ready_list);
+
+ QSIMPLEQ_REMOVE_HEAD(ready_list, next);
+
+ cqe_handler->cb(cqe_handler);
+ }
+
+ defer_call_end();
+
+ qemu_bh_cancel(ctx->cqe_handler_bh);
+}
+
+/* Returns true if a handler became ready */
+static bool process_cqe(AioContext *ctx,
+ AioHandlerList *ready_list,
+ struct io_uring_cqe *cqe)
+{
+ CqeHandler *cqe_handler = io_uring_cqe_get_data(cqe);
+
+ /* poll_timeout and poll_remove have a zero user_data field */
+ if (!cqe_handler) {
+ return false;
+ }
+
+ /*
+ * Special handling for AioHandler cqes. They need ready_list and have a
+ * return value.
+ */
+ if (cqe_handler->cb == fdmon_special_cqe_handler) {
+ AioHandler *node = container_of(cqe_handler, AioHandler, cqe_handler);
+ return process_cqe_aio_handler(ctx, ready_list, node, cqe);
+ }
+
+ cqe_handler->cqe = *cqe;
+ QSIMPLEQ_INSERT_TAIL(&ctx->cqe_handler_ready_list, cqe_handler, next);
+ qemu_bh_schedule(ctx->cqe_handler_bh);
+ return false;
+}
+
static int process_cq_ring(AioContext *ctx, AioHandlerList *ready_list)
{
struct io_uring *ring = &ctx->fdmon_io_uring;
@@ -368,6 +438,7 @@ static const FDMonOps fdmon_io_uring_ops = {
.gsource_prepare = fdmon_io_uring_gsource_prepare,
.gsource_check = fdmon_io_uring_gsource_check,
.gsource_dispatch = fdmon_io_uring_gsource_dispatch,
+ .add_sqe = fdmon_io_uring_add_sqe,
};
void fdmon_io_uring_setup(AioContext *ctx, Error **errp)
@@ -383,6 +454,8 @@ void fdmon_io_uring_setup(AioContext *ctx, Error **errp)
}
QSLIST_INIT(&ctx->submit_list);
+ QSIMPLEQ_INIT(&ctx->cqe_handler_ready_list);
+ ctx->cqe_handler_bh = aio_bh_new(ctx, cqe_handler_bh, ctx);
ctx->fdmon_ops = &fdmon_io_uring_ops;
ctx->io_uring_fd_tag = g_source_add_unix_fd(&ctx->source,
ctx->fdmon_io_uring.ring_fd, G_IO_IN);
@@ -390,33 +463,38 @@ void fdmon_io_uring_setup(AioContext *ctx, Error **errp)
void fdmon_io_uring_destroy(AioContext *ctx)
{
- if (ctx->fdmon_ops == &fdmon_io_uring_ops) {
- AioHandler *node;
+ AioHandler *node;
- io_uring_queue_exit(&ctx->fdmon_io_uring);
+ if (ctx->fdmon_ops != &fdmon_io_uring_ops) {
+ return;
+ }
- /* Move handlers due to be removed onto the deleted list */
- while ((node = QSLIST_FIRST_RCU(&ctx->submit_list))) {
- unsigned flags = qatomic_fetch_and(&node->flags,
- ~(FDMON_IO_URING_PENDING |
- FDMON_IO_URING_ADD |
- FDMON_IO_URING_REMOVE |
- FDMON_IO_URING_DELETE_AIO_HANDLER));
+ io_uring_queue_exit(&ctx->fdmon_io_uring);
- if ((flags & FDMON_IO_URING_REMOVE) ||
- (flags & FDMON_IO_URING_DELETE_AIO_HANDLER)) {
- QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers,
- node, node_deleted);
- }
+ /* Move handlers due to be removed onto the deleted list */
+ while ((node = QSLIST_FIRST_RCU(&ctx->submit_list))) {
+ unsigned flags = qatomic_fetch_and(&node->flags,
+ ~(FDMON_IO_URING_PENDING |
+ FDMON_IO_URING_ADD |
+ FDMON_IO_URING_REMOVE |
+ FDMON_IO_URING_DELETE_AIO_HANDLER));
- QSLIST_REMOVE_HEAD_RCU(&ctx->submit_list, node_submitted);
+ if ((flags & FDMON_IO_URING_REMOVE) ||
+ (flags & FDMON_IO_URING_DELETE_AIO_HANDLER)) {
+ QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers,
+ node, node_deleted);
}
- g_source_remove_unix_fd(&ctx->source, ctx->io_uring_fd_tag);
- ctx->io_uring_fd_tag = NULL;
-
- qemu_lockcnt_lock(&ctx->list_lock);
- fdmon_poll_downgrade(ctx);
- qemu_lockcnt_unlock(&ctx->list_lock);
+ QSLIST_REMOVE_HEAD_RCU(&ctx->submit_list, node_submitted);
}
+
+ g_source_remove_unix_fd(&ctx->source, ctx->io_uring_fd_tag);
+ ctx->io_uring_fd_tag = NULL;
+
+ assert(QSIMPLEQ_EMPTY(&ctx->cqe_handler_ready_list));
+ qemu_bh_delete(ctx->cqe_handler_bh);
+
+ qemu_lockcnt_lock(&ctx->list_lock);
+ fdmon_poll_downgrade(ctx);
+ qemu_lockcnt_unlock(&ctx->list_lock);
}
--
2.51.0
^ permalink raw reply related [flat|nested] 25+ messages in thread* Re: [PATCH v4 09/12] aio-posix: add aio_add_sqe() API for user-defined io_uring requests
2025-09-10 17:57 ` [PATCH v4 09/12] aio-posix: add aio_add_sqe() API for user-defined io_uring requests Stefan Hajnoczi
@ 2025-10-10 15:23 ` Kevin Wolf
2025-10-10 16:20 ` Kevin Wolf
0 siblings, 1 reply; 25+ messages in thread
From: Kevin Wolf @ 2025-10-10 15:23 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Aarushi Mehta, Fam Zheng, Stefano Garzarella,
Hanna Czenczek, eblake, qemu-block, hibriansong, Stefan Weil,
Paolo Bonzini
Am 10.09.2025 um 19:57 hat Stefan Hajnoczi geschrieben:
> Introduce the aio_add_sqe() API for submitting io_uring requests in the
> current AioContext. This allows other components in QEMU, like the block
> layer, to take advantage of io_uring features without creating their own
> io_uring context.
>
> This API supports nested event loops just like file descriptor
> monitoring and BHs do. This comes at a complexity cost: a BH is required
> to dispatch CQE callbacks and they are placed on a list so that a nested
> event loop can invoke its parent's pending CQE callbacks. If you're
> wondering why CqeHandler exists instead of just a callback function
> pointer, this is why.
This is a mechanism that we know from other places in the code like the
Linux AIO or indeed the old io_uring block driver code, because a BH is
the only thing that makes sure that the main loop will call into the
code again later.
Do we really need it here, though? This _is_ literally the main loop
implementation, we don't have to make the main loop call us.
.need_wait() checks io_uring_cq_ready(), so as long as there are
unprocessed completions, we know that .wait() will be called in nested
event loops. We just can't take more than one completion out of the
queue to process them later for this to work, but have to process them
one by one as we get them from the ring. But that's what we already do.
Am I missing something?
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
> v2:
> - Fix pre_sqe -> prep_sqe typo [Eric]
> - Add #endif terminator comment [Eric]
> ---
> include/block/aio.h | 84 ++++++++++++++++++++++-
> util/aio-posix.h | 1 +
> util/aio-posix.c | 9 +++
> util/fdmon-io_uring.c | 152 ++++++++++++++++++++++++++++++++----------
> 4 files changed, 208 insertions(+), 38 deletions(-)
>
> diff --git a/include/block/aio.h b/include/block/aio.h
> index d919d7c8f4..56ea0d47b7 100644
> --- a/include/block/aio.h
> +++ b/include/block/aio.h
> @@ -61,6 +61,27 @@ typedef struct LuringState LuringState;
> /* Is polling disabled? */
> bool aio_poll_disabled(AioContext *ctx);
>
> +#ifdef CONFIG_LINUX_IO_URING
> +/*
> + * Each io_uring request must have a unique CqeHandler that processes the cqe.
> + * The lifetime of a CqeHandler must be at least from aio_add_sqe() until
> + * ->cb() invocation.
> + */
> +typedef struct CqeHandler CqeHandler;
> +struct CqeHandler {
> + /* Called by the AioContext when the request has completed */
> + void (*cb)(CqeHandler *handler);
> +
> + /* Used internally, do not access this */
> + QSIMPLEQ_ENTRY(CqeHandler) next;
> +
> + /* This field is filled in before ->cb() is called */
> + struct io_uring_cqe cqe;
> +};
> +
> +typedef QSIMPLEQ_HEAD(, CqeHandler) CqeHandlerSimpleQ;
> +#endif /* CONFIG_LINUX_IO_URING */
> +
> /* Callbacks for file descriptor monitoring implementations */
> typedef struct {
> /*
> @@ -138,6 +159,27 @@ typedef struct {
> * Called with list_lock incremented.
> */
> void (*gsource_dispatch)(AioContext *ctx, AioHandlerList *ready_list);
> +
> +#ifdef CONFIG_LINUX_IO_URING
> + /**
> + * aio_add_sqe: Add an io_uring sqe for submission.
s/aio_add_sqe/add_sqe/
> + * @prep_sqe: invoked with an sqe that should be prepared for submission
> + * @opaque: user-defined argument to @prep_sqe()
> + * @cqe_handler: the unique cqe handler associated with this request
> + *
> + * The caller's @prep_sqe() function is invoked to fill in the details of
> + * the sqe. Do not call io_uring_sqe_set_data() on this sqe.
> + *
> + * The kernel may see the sqe as soon as @prep_sqe() returns or it may take
> + * until the next event loop iteration.
> + *
> + * This function is called from the current AioContext and is not
> + * thread-safe.
> + */
> + void (*add_sqe)(AioContext *ctx,
> + void (*prep_sqe)(struct io_uring_sqe *sqe, void *opaque),
> + void *opaque, CqeHandler *cqe_handler);
> +#endif /* CONFIG_LINUX_IO_URING */
> } FDMonOps;
>
> /*
> @@ -255,7 +297,11 @@ struct AioContext {
> struct io_uring fdmon_io_uring;
> AioHandlerSList submit_list;
> gpointer io_uring_fd_tag;
> -#endif
> +
> + /* Pending callback state for cqe handlers */
> + CqeHandlerSimpleQ cqe_handler_ready_list;
> + QEMUBH *cqe_handler_bh;
> +#endif /* CONFIG_LINUX_IO_URING */
>
> /* TimerLists for calling timers - one per clock type. Has its own
> * locking.
> @@ -761,4 +807,40 @@ void aio_context_set_aio_params(AioContext *ctx, int64_t max_batch);
> */
> void aio_context_set_thread_pool_params(AioContext *ctx, int64_t min,
> int64_t max, Error **errp);
> +
> +#ifdef CONFIG_LINUX_IO_URING
> +/**
> + * aio_has_io_uring: Return whether io_uring is available.
> + *
> + * io_uring is either available in all AioContexts or in none, so this only
> + * needs to be called once from within any thread's AioContext.
> + */
> +static inline bool aio_has_io_uring(void)
> +{
> + AioContext *ctx = qemu_get_current_aio_context();
> + return ctx->fdmon_ops->add_sqe;
> +}
> +
> +/**
> + * aio_add_sqe: Add an io_uring sqe for submission.
> + * @prep_sqe: invoked with an sqe that should be prepared for submission
> + * @opaque: user-defined argument to @prep_sqe()
> + * @cqe_handler: the unique cqe handler associated with this request
> + *
> + * The caller's @prep_sqe() function is invoked to fill in the details of the
> + * sqe. Do not call io_uring_sqe_set_data() on this sqe.
> + *
> + * The sqe is submitted by the current AioContext. The kernel may see the sqe
> + * as soon as @prep_sqe() returns or it may take until the next event loop
> + * iteration.
> + *
> + * When the AioContext is destroyed, pending sqes are ignored and their
> + * CqeHandlers are not invoked.
> + *
> + * This function must be called only when aio_has_io_uring() returns true.
> + */
> +void aio_add_sqe(void (*prep_sqe)(struct io_uring_sqe *sqe, void *opaque),
> + void *opaque, CqeHandler *cqe_handler);
> +#endif /* CONFIG_LINUX_IO_URING */
> +
> #endif
> diff --git a/util/aio-posix.h b/util/aio-posix.h
> index 6f9d97d866..57ef801a5f 100644
> --- a/util/aio-posix.h
> +++ b/util/aio-posix.h
> @@ -36,6 +36,7 @@ struct AioHandler {
> #ifdef CONFIG_LINUX_IO_URING
> QSLIST_ENTRY(AioHandler) node_submitted;
> unsigned flags; /* see fdmon-io_uring.c */
> + CqeHandler cqe_handler;
Can we either rename this or add a comment to clarify that this is for
fdmon-internal requests like POLL_ADD/REMOVE?
> #endif
> int64_t poll_idle_timeout; /* when to stop userspace polling */
> bool poll_ready; /* has polling detected an event? */
> diff --git a/util/aio-posix.c b/util/aio-posix.c
> index 800b4debbf..df945312b3 100644
> --- a/util/aio-posix.c
> +++ b/util/aio-posix.c
> +/* Returns true if a handler became ready */
> +static bool process_cqe(AioContext *ctx,
> + AioHandlerList *ready_list,
> + struct io_uring_cqe *cqe)
> +{
> + CqeHandler *cqe_handler = io_uring_cqe_get_data(cqe);
> +
> + /* poll_timeout and poll_remove have a zero user_data field */
> + if (!cqe_handler) {
> + return false;
> + }
> +
> + /*
> + * Special handling for AioHandler cqes. They need ready_list and have a
> + * return value.
> + */
> + if (cqe_handler->cb == fdmon_special_cqe_handler) {
> + AioHandler *node = container_of(cqe_handler, AioHandler, cqe_handler);
> + return process_cqe_aio_handler(ctx, ready_list, node, cqe);
> + }
Is the reason why we special case internal requests (instead of just
using the normal mechanism where the callback is actually called) the
overhead of going through a BH that we don't want to have for every
event?
But if so, why are we okay with the same overhead for other requests?
> +
> + cqe_handler->cqe = *cqe;
> + QSIMPLEQ_INSERT_TAIL(&ctx->cqe_handler_ready_list, cqe_handler, next);
> + qemu_bh_schedule(ctx->cqe_handler_bh);
> + return false;
> +}
> +
> static int process_cq_ring(AioContext *ctx, AioHandlerList *ready_list)
> {
> struct io_uring *ring = &ctx->fdmon_io_uring;
> @@ -368,6 +438,7 @@ static const FDMonOps fdmon_io_uring_ops = {
> .gsource_prepare = fdmon_io_uring_gsource_prepare,
> .gsource_check = fdmon_io_uring_gsource_check,
> .gsource_dispatch = fdmon_io_uring_gsource_dispatch,
> + .add_sqe = fdmon_io_uring_add_sqe,
> };
>
> void fdmon_io_uring_setup(AioContext *ctx, Error **errp)
> @@ -383,6 +454,8 @@ void fdmon_io_uring_setup(AioContext *ctx, Error **errp)
> }
>
> QSLIST_INIT(&ctx->submit_list);
> + QSIMPLEQ_INIT(&ctx->cqe_handler_ready_list);
> + ctx->cqe_handler_bh = aio_bh_new(ctx, cqe_handler_bh, ctx);
> ctx->fdmon_ops = &fdmon_io_uring_ops;
> ctx->io_uring_fd_tag = g_source_add_unix_fd(&ctx->source,
> ctx->fdmon_io_uring.ring_fd, G_IO_IN);
> @@ -390,33 +463,38 @@ void fdmon_io_uring_setup(AioContext *ctx, Error **errp)
>
> void fdmon_io_uring_destroy(AioContext *ctx)
> {
> - if (ctx->fdmon_ops == &fdmon_io_uring_ops) {
> - AioHandler *node;
> + AioHandler *node;
>
> - io_uring_queue_exit(&ctx->fdmon_io_uring);
> + if (ctx->fdmon_ops != &fdmon_io_uring_ops) {
> + return;
> + }
>
> - /* Move handlers due to be removed onto the deleted list */
> - while ((node = QSLIST_FIRST_RCU(&ctx->submit_list))) {
> - unsigned flags = qatomic_fetch_and(&node->flags,
> - ~(FDMON_IO_URING_PENDING |
> - FDMON_IO_URING_ADD |
> - FDMON_IO_URING_REMOVE |
> - FDMON_IO_URING_DELETE_AIO_HANDLER));
> + io_uring_queue_exit(&ctx->fdmon_io_uring);
>
> - if ((flags & FDMON_IO_URING_REMOVE) ||
> - (flags & FDMON_IO_URING_DELETE_AIO_HANDLER)) {
> - QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers,
> - node, node_deleted);
> - }
> + /* Move handlers due to be removed onto the deleted list */
> + while ((node = QSLIST_FIRST_RCU(&ctx->submit_list))) {
> + unsigned flags = qatomic_fetch_and(&node->flags,
> + ~(FDMON_IO_URING_PENDING |
> + FDMON_IO_URING_ADD |
> + FDMON_IO_URING_REMOVE |
> + FDMON_IO_URING_DELETE_AIO_HANDLER));
>
> - QSLIST_REMOVE_HEAD_RCU(&ctx->submit_list, node_submitted);
> + if ((flags & FDMON_IO_URING_REMOVE) ||
> + (flags & FDMON_IO_URING_DELETE_AIO_HANDLER)) {
> + QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers,
> + node, node_deleted);
> }
>
> - g_source_remove_unix_fd(&ctx->source, ctx->io_uring_fd_tag);
> - ctx->io_uring_fd_tag = NULL;
> -
> - qemu_lockcnt_lock(&ctx->list_lock);
> - fdmon_poll_downgrade(ctx);
> - qemu_lockcnt_unlock(&ctx->list_lock);
> + QSLIST_REMOVE_HEAD_RCU(&ctx->submit_list, node_submitted);
> }
> +
> + g_source_remove_unix_fd(&ctx->source, ctx->io_uring_fd_tag);
> + ctx->io_uring_fd_tag = NULL;
> +
> + assert(QSIMPLEQ_EMPTY(&ctx->cqe_handler_ready_list));
> + qemu_bh_delete(ctx->cqe_handler_bh);
These are the only two lines that are actually added in the last hunk
apart from switching from a big if to an early return. I wonder if the
improved readability of the diff would be worth a separate patch just
for the switch to the early return. (But git diff -w is helpful enough
once you realise what's going on.)
> + qemu_lockcnt_lock(&ctx->list_lock);
> + fdmon_poll_downgrade(ctx);
> + qemu_lockcnt_unlock(&ctx->list_lock);
> }
Kevin
^ permalink raw reply [flat|nested] 25+ messages in thread* Re: [PATCH v4 09/12] aio-posix: add aio_add_sqe() API for user-defined io_uring requests
2025-10-10 15:23 ` Kevin Wolf
@ 2025-10-10 16:20 ` Kevin Wolf
0 siblings, 0 replies; 25+ messages in thread
From: Kevin Wolf @ 2025-10-10 16:20 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Aarushi Mehta, Fam Zheng, Stefano Garzarella,
Hanna Czenczek, eblake, qemu-block, hibriansong, Stefan Weil,
Paolo Bonzini
Am 10.10.2025 um 17:23 hat Kevin Wolf geschrieben:
> Am 10.09.2025 um 19:57 hat Stefan Hajnoczi geschrieben:
> > Introduce the aio_add_sqe() API for submitting io_uring requests in the
> > current AioContext. This allows other components in QEMU, like the block
> > layer, to take advantage of io_uring features without creating their own
> > io_uring context.
> >
> > This API supports nested event loops just like file descriptor
> > monitoring and BHs do. This comes at a complexity cost: a BH is required
> > to dispatch CQE callbacks and they are placed on a list so that a nested
> > event loop can invoke its parent's pending CQE callbacks. If you're
> > wondering why CqeHandler exists instead of just a callback function
> > pointer, this is why.
>
> This is a mechanism that we know from other places in the code like the
> Linux AIO or indeed the old io_uring block driver code, because a BH is
> the only thing that makes sure that the main loop will call into the
> code again later.
>
> Do we really need it here, though? This _is_ literally the main loop
> implementation, we don't have to make the main loop call us.
> .need_wait() checks io_uring_cq_ready(), so as long as there are
> unprocessed completions, we know that .wait() will be called in nested
> event loops. We just can't take more than one completion out of the
> queue to process them later for this to work, but have to process them
> one by one as we get them from the ring. But that's what we already do.
>
> Am I missing something?
I think what I missed is that we probably don't want to call arbitrary
callbacks from .wait(), but only in the dispatching phase. At the same
time, we need to fill the ready_list during .wait() and can't do that
later, so we do have to go through all CQEs here. The only way I can see
to get rid of the extra list - which I would really like to see - would
be processing the CQEs twice (once during .wait() for the internal ones
and once during the dispatch phase for the add_sqe() ones). That's a bit
annoying.
Either way, even if we keep the list, scheduling and cancelling BHs from
the fdmon still doesn't feel quite right to me. I wonder if we shouldn't
introduce a .dispatch() callback in FDMonOps that could run the
cqe_handler_ready_list for fdmon-io_uring. That would also make the
interface more consistent with the set of callbacks we have for GSource,
and maybe eventually simplify deduplicating them.
Then you also don't need the ugly optimisation in the next patch that
fixes the slowness of scheduling BHs in .wait() by moving io_uring code
to the AioContext core.
Kevin
^ permalink raw reply [flat|nested] 25+ messages in thread
* [PATCH v4 10/12] aio-posix: avoid EventNotifier for cqe_handler_bh
2025-09-10 17:56 [PATCH v4 00/12] aio: add the aio_add_sqe() io_uring API Stefan Hajnoczi
` (8 preceding siblings ...)
2025-09-10 17:57 ` [PATCH v4 09/12] aio-posix: add aio_add_sqe() API for user-defined io_uring requests Stefan Hajnoczi
@ 2025-09-10 17:57 ` Stefan Hajnoczi
2025-09-10 17:57 ` [PATCH v4 11/12] block/io_uring: use aio_add_sqe() Stefan Hajnoczi
2025-09-10 17:57 ` [PATCH v4 12/12] block/io_uring: use non-vectored read/write when possible Stefan Hajnoczi
11 siblings, 0 replies; 25+ messages in thread
From: Stefan Hajnoczi @ 2025-09-10 17:57 UTC (permalink / raw)
To: qemu-devel
Cc: Aarushi Mehta, Fam Zheng, Stefano Garzarella, Hanna Czenczek,
eblake, Stefan Hajnoczi, Kevin Wolf, qemu-block, hibriansong,
Stefan Weil, Paolo Bonzini
fdmon_ops->wait() is called with notify_me enabled. This makes it an
expensive place to call qemu_bh_schedule() because aio_notify() invokes
write(2) on the EventNotifier.
Moving qemu_bh_schedule() after notify_me is reset improves IOPS from
270k to 300k IOPS with --blockdev file,aio=io_uring.
I considered alternatives:
1. Introducing a variant of qemu_bh_schedule() that skips aio_notify().
This only makes sense within the AioContext and fdmon implementation
itself and is therefore a specialized internal API. I don't like
that.
2. Changing fdmon_ops->wait() so implementors can reset notify_me
themselves. This makes things complex and the other fdmon
implementations don't need it, so it doesn't seem like a good
solution.
So in the end I moved the qemu_bh_schedule() call from fdmon-io_uring.c
to aio-posix.c. It's ugly but straightforward.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
util/aio-posix.c | 11 +++++++++++
util/fdmon-io_uring.c | 11 ++++++++++-
2 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/util/aio-posix.c b/util/aio-posix.c
index df945312b3..20b11e5650 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -700,6 +700,17 @@ bool aio_poll(AioContext *ctx, bool blocking)
qatomic_read(&ctx->notify_me) - 2);
}
+#ifdef CONFIG_LINUX_IO_URING
+ /*
+ * This is part of fdmon-io_uring.c but it's more efficient to do it here
+ * after notify_me has been reset. That way qemu_bh_schedule() ->
+ * aio_notify() does not write the EventNotifier.
+ */
+ if (!QSIMPLEQ_EMPTY(&ctx->cqe_handler_ready_list)) {
+ qemu_bh_schedule(ctx->cqe_handler_bh);
+ }
+#endif
+
aio_notify_accept(ctx);
/* Calculate blocked time for adaptive polling */
diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c
index 7f7c50907d..9ed02597d6 100644
--- a/util/fdmon-io_uring.c
+++ b/util/fdmon-io_uring.c
@@ -334,8 +334,12 @@ static bool process_cqe(AioContext *ctx,
}
cqe_handler->cqe = *cqe;
+
+ /*
+ * aio_poll() and fdmon_io_uring_gsource_dispatch() schedule cqe_handler_bh
+ * when the list is non-empty.
+ */
QSIMPLEQ_INSERT_TAIL(&ctx->cqe_handler_ready_list, cqe_handler, next);
- qemu_bh_schedule(ctx->cqe_handler_bh);
return false;
}
@@ -386,6 +390,11 @@ static void fdmon_io_uring_gsource_dispatch(AioContext *ctx,
AioHandlerList *ready_list)
{
process_cq_ring(ctx, ready_list);
+
+ /* Ensure CqeHandlers enqueued by process_cq_ring() will run */
+ if (!QSIMPLEQ_EMPTY(&ctx->cqe_handler_ready_list)) {
+ qemu_bh_schedule(ctx->cqe_handler_bh);
+ }
}
static int fdmon_io_uring_wait(AioContext *ctx, AioHandlerList *ready_list,
--
2.51.0
^ permalink raw reply related [flat|nested] 25+ messages in thread* [PATCH v4 11/12] block/io_uring: use aio_add_sqe()
2025-09-10 17:56 [PATCH v4 00/12] aio: add the aio_add_sqe() io_uring API Stefan Hajnoczi
` (9 preceding siblings ...)
2025-09-10 17:57 ` [PATCH v4 10/12] aio-posix: avoid EventNotifier for cqe_handler_bh Stefan Hajnoczi
@ 2025-09-10 17:57 ` Stefan Hajnoczi
2025-09-10 17:57 ` [PATCH v4 12/12] block/io_uring: use non-vectored read/write when possible Stefan Hajnoczi
11 siblings, 0 replies; 25+ messages in thread
From: Stefan Hajnoczi @ 2025-09-10 17:57 UTC (permalink / raw)
To: qemu-devel
Cc: Aarushi Mehta, Fam Zheng, Stefano Garzarella, Hanna Czenczek,
eblake, Stefan Hajnoczi, Kevin Wolf, qemu-block, hibriansong,
Stefan Weil, Paolo Bonzini
AioContext has its own io_uring instance for file descriptor monitoring.
The disk I/O io_uring code was developed separately. Originally I
thought the characteristics of file descriptor monitoring and disk I/O
were too different, requiring separate io_uring instances.
Now it has become clear to me that it's feasible to share a single
io_uring instance for file descriptor monitoring and disk I/O. We're not
using io_uring's IOPOLL feature or anything else that would require a
separate instance.
Unify block/io_uring.c and util/fdmon-io_uring.c using the new
aio_add_sqe() API that allows user-defined io_uring sqe submission. Now
block/io_uring.c just needs to submit readv/writev/fsync and most of the
io_uring-specific logic is handled by fdmon-io_uring.c.
There are two immediate advantages:
1. Fewer system calls. There is no need to monitor the disk I/O io_uring
ring fd from the file descriptor monitoring io_uring instance. Disk
I/O completions are now picked up directly. Also, sqes are
accumulated in the sq ring until the end of the event loop iteration
and there are fewer io_uring_enter(2) syscalls.
2. Less code duplication.
Note that error_setg() messages are not supposed to end with
punctuation, so I removed a '.' for the non-io_uring build error
message.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
include/block/aio.h | 7 -
include/block/raw-aio.h | 5 -
block/file-posix.c | 40 ++--
block/io_uring.c | 489 ++++++++++------------------------------
stubs/io_uring.c | 32 ---
util/async.c | 35 ---
util/fdmon-io_uring.c | 6 +
block/trace-events | 12 +-
stubs/meson.build | 3 -
util/trace-events | 4 +
10 files changed, 140 insertions(+), 493 deletions(-)
delete mode 100644 stubs/io_uring.c
diff --git a/include/block/aio.h b/include/block/aio.h
index 56ea0d47b7..60e76d4227 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -291,8 +291,6 @@ struct AioContext {
struct LinuxAioState *linux_aio;
#endif
#ifdef CONFIG_LINUX_IO_URING
- LuringState *linux_io_uring;
-
/* State for file descriptor monitoring using Linux io_uring */
struct io_uring fdmon_io_uring;
AioHandlerSList submit_list;
@@ -597,11 +595,6 @@ struct LinuxAioState *aio_setup_linux_aio(AioContext *ctx, Error **errp);
/* Return the LinuxAioState bound to this AioContext */
struct LinuxAioState *aio_get_linux_aio(AioContext *ctx);
-/* Setup the LuringState bound to this AioContext */
-LuringState *aio_setup_linux_io_uring(AioContext *ctx, Error **errp);
-
-/* Return the LuringState bound to this AioContext */
-LuringState *aio_get_linux_io_uring(AioContext *ctx);
/**
* aio_timer_new_with_attrs:
* @ctx: the aio context
diff --git a/include/block/raw-aio.h b/include/block/raw-aio.h
index 6570244496..30e5fc9a9f 100644
--- a/include/block/raw-aio.h
+++ b/include/block/raw-aio.h
@@ -74,15 +74,10 @@ static inline bool laio_has_fua(void)
#endif
/* io_uring.c - Linux io_uring implementation */
#ifdef CONFIG_LINUX_IO_URING
-LuringState *luring_init(Error **errp);
-void luring_cleanup(LuringState *s);
-
/* luring_co_submit: submit I/O requests in the thread's current AioContext. */
int coroutine_fn luring_co_submit(BlockDriverState *bs, int fd, uint64_t offset,
QEMUIOVector *qiov, int type,
BdrvRequestFlags flags);
-void luring_detach_aio_context(LuringState *s, AioContext *old_context);
-void luring_attach_aio_context(LuringState *s, AioContext *new_context);
bool luring_has_fua(void);
#else
static inline bool luring_has_fua(void)
diff --git a/block/file-posix.c b/block/file-posix.c
index 8c738674ce..8b7c02d19a 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -755,14 +755,23 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
}
#endif /* !defined(CONFIG_LINUX_AIO) */
-#ifndef CONFIG_LINUX_IO_URING
if (s->use_linux_io_uring) {
+#ifdef CONFIG_LINUX_IO_URING
+ if (!aio_has_io_uring()) {
+ error_setg(errp, "aio=io_uring was specified, but is not "
+ "available (disabled via io_uring_disabled "
+ "sysctl or blocked by container runtime "
+ "seccomp policy?)");
+ ret = -EINVAL;
+ goto fail;
+ }
+#else
error_setg(errp, "aio=io_uring was specified, but is not supported "
- "in this build.");
+ "in this build");
ret = -EINVAL;
goto fail;
- }
#endif /* !defined(CONFIG_LINUX_IO_URING) */
+ }
s->has_discard = true;
s->has_write_zeroes = true;
@@ -2522,27 +2531,6 @@ static bool bdrv_qiov_is_aligned(BlockDriverState *bs, QEMUIOVector *qiov)
return true;
}
-#ifdef CONFIG_LINUX_IO_URING
-static inline bool raw_check_linux_io_uring(BDRVRawState *s)
-{
- Error *local_err = NULL;
- AioContext *ctx;
-
- if (!s->use_linux_io_uring) {
- return false;
- }
-
- ctx = qemu_get_current_aio_context();
- if (unlikely(!aio_setup_linux_io_uring(ctx, &local_err))) {
- error_reportf_err(local_err, "Unable to use linux io_uring, "
- "falling back to thread pool: ");
- s->use_linux_io_uring = false;
- return false;
- }
- return true;
-}
-#endif
-
#ifdef CONFIG_LINUX_AIO
static inline bool raw_check_linux_aio(BDRVRawState *s)
{
@@ -2595,7 +2583,7 @@ raw_co_prw(BlockDriverState *bs, int64_t *offset_ptr, uint64_t bytes,
if (s->needs_alignment && !bdrv_qiov_is_aligned(bs, qiov)) {
type |= QEMU_AIO_MISALIGNED;
#ifdef CONFIG_LINUX_IO_URING
- } else if (raw_check_linux_io_uring(s)) {
+ } else if (s->use_linux_io_uring) {
assert(qiov->size == bytes);
ret = luring_co_submit(bs, s->fd, offset, qiov, type, flags);
goto out;
@@ -2692,7 +2680,7 @@ static int coroutine_fn raw_co_flush_to_disk(BlockDriverState *bs)
};
#ifdef CONFIG_LINUX_IO_URING
- if (raw_check_linux_io_uring(s)) {
+ if (s->use_linux_io_uring) {
return luring_co_submit(bs, s->fd, 0, NULL, QEMU_AIO_FLUSH, 0);
}
#endif
diff --git a/block/io_uring.c b/block/io_uring.c
index dd4f304910..dd930ee57e 100644
--- a/block/io_uring.c
+++ b/block/io_uring.c
@@ -11,28 +11,20 @@
#include "qemu/osdep.h"
#include <liburing.h>
#include "block/aio.h"
-#include "qemu/queue.h"
#include "block/block.h"
#include "block/raw-aio.h"
#include "qemu/coroutine.h"
-#include "qemu/defer-call.h"
-#include "qapi/error.h"
#include "system/block-backend.h"
#include "trace.h"
-/* Only used for assertions. */
-#include "qemu/coroutine_int.h"
-
-/* io_uring ring size */
-#define MAX_ENTRIES 128
-
-typedef struct LuringAIOCB {
+typedef struct {
Coroutine *co;
- struct io_uring_sqe sqeq;
- ssize_t ret;
QEMUIOVector *qiov;
- bool is_read;
- QSIMPLEQ_ENTRY(LuringAIOCB) next;
+ uint64_t offset;
+ ssize_t ret;
+ int type;
+ int fd;
+ BdrvRequestFlags flags;
/*
* Buffered reads may require resubmission, see
@@ -40,36 +32,51 @@ typedef struct LuringAIOCB {
*/
int total_read;
QEMUIOVector resubmit_qiov;
-} LuringAIOCB;
-typedef struct LuringQueue {
- unsigned int in_queue;
- unsigned int in_flight;
- bool blocked;
- QSIMPLEQ_HEAD(, LuringAIOCB) submit_queue;
-} LuringQueue;
+ CqeHandler cqe_handler;
+} LuringRequest;
-struct LuringState {
- AioContext *aio_context;
-
- struct io_uring ring;
-
- /* No locking required, only accessed from AioContext home thread */
- LuringQueue io_q;
-
- QEMUBH *completion_bh;
-};
-
-/**
- * luring_resubmit:
- *
- * Resubmit a request by appending it to submit_queue. The caller must ensure
- * that ioq_submit() is called later so that submit_queue requests are started.
- */
-static void luring_resubmit(LuringState *s, LuringAIOCB *luringcb)
+static void luring_prep_sqe(struct io_uring_sqe *sqe, void *opaque)
{
- QSIMPLEQ_INSERT_TAIL(&s->io_q.submit_queue, luringcb, next);
- s->io_q.in_queue++;
+ LuringRequest *req = opaque;
+ QEMUIOVector *qiov = req->qiov;
+ uint64_t offset = req->offset;
+ int fd = req->fd;
+ BdrvRequestFlags flags = req->flags;
+
+ switch (req->type) {
+ case QEMU_AIO_WRITE:
+#ifdef HAVE_IO_URING_PREP_WRITEV2
+ {
+ int luring_flags = (flags & BDRV_REQ_FUA) ? RWF_DSYNC : 0;
+ io_uring_prep_writev2(sqe, fd, qiov->iov,
+ qiov->niov, offset, luring_flags);
+ }
+#else
+ assert(flags == 0);
+ io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset);
+#endif
+ break;
+ case QEMU_AIO_ZONE_APPEND:
+ io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset);
+ break;
+ case QEMU_AIO_READ:
+ {
+ if (req->resubmit_qiov.iov != NULL) {
+ qiov = &req->resubmit_qiov;
+ }
+ io_uring_prep_readv(sqe, fd, qiov->iov, qiov->niov,
+ offset + req->total_read);
+ break;
+ }
+ case QEMU_AIO_FLUSH:
+ io_uring_prep_fsync(sqe, fd, IORING_FSYNC_DATASYNC);
+ break;
+ default:
+ fprintf(stderr, "%s: invalid AIO request type, aborting 0x%x.\n",
+ __func__, req->type);
+ abort();
+ }
}
/**
@@ -78,385 +85,115 @@ static void luring_resubmit(LuringState *s, LuringAIOCB *luringcb)
* Short reads are rare but may occur. The remaining read request needs to be
* resubmitted.
*/
-static void luring_resubmit_short_read(LuringState *s, LuringAIOCB *luringcb,
- int nread)
+static void luring_resubmit_short_read(LuringRequest *req, int nread)
{
QEMUIOVector *resubmit_qiov;
size_t remaining;
- trace_luring_resubmit_short_read(s, luringcb, nread);
+ trace_luring_resubmit_short_read(req, nread);
/* Update read position */
- luringcb->total_read += nread;
- remaining = luringcb->qiov->size - luringcb->total_read;
+ req->total_read += nread;
+ remaining = req->qiov->size - req->total_read;
/* Shorten qiov */
- resubmit_qiov = &luringcb->resubmit_qiov;
+ resubmit_qiov = &req->resubmit_qiov;
if (resubmit_qiov->iov == NULL) {
- qemu_iovec_init(resubmit_qiov, luringcb->qiov->niov);
+ qemu_iovec_init(resubmit_qiov, req->qiov->niov);
} else {
qemu_iovec_reset(resubmit_qiov);
}
- qemu_iovec_concat(resubmit_qiov, luringcb->qiov, luringcb->total_read,
- remaining);
+ qemu_iovec_concat(resubmit_qiov, req->qiov, req->total_read, remaining);
- /* Update sqe */
- luringcb->sqeq.off += nread;
- luringcb->sqeq.addr = (uintptr_t)luringcb->resubmit_qiov.iov;
- luringcb->sqeq.len = luringcb->resubmit_qiov.niov;
-
- luring_resubmit(s, luringcb);
+ aio_add_sqe(luring_prep_sqe, req, &req->cqe_handler);
}
-/**
- * luring_process_completions:
- * @s: AIO state
- *
- * Fetches completed I/O requests, consumes cqes and invokes their callbacks
- * The function is somewhat tricky because it supports nested event loops, for
- * example when a request callback invokes aio_poll().
- *
- * Function schedules BH completion so it can be called again in a nested
- * event loop. When there are no events left to complete the BH is being
- * canceled.
- *
- */
-static void luring_process_completions(LuringState *s)
+static void luring_cqe_handler(CqeHandler *cqe_handler)
{
- struct io_uring_cqe *cqes;
- int total_bytes;
+ LuringRequest *req = container_of(cqe_handler, LuringRequest, cqe_handler);
+ int ret = cqe_handler->cqe.res;
- defer_call_begin();
+ trace_luring_cqe_handler(req, ret);
- /*
- * Request completion callbacks can run the nested event loop.
- * Schedule ourselves so the nested event loop will "see" remaining
- * completed requests and process them. Without this, completion
- * callbacks that wait for other requests using a nested event loop
- * would hang forever.
- *
- * This workaround is needed because io_uring uses poll_wait, which
- * is woken up when new events are added to the uring, thus polling on
- * the same uring fd will block unless more events are received.
- *
- * Other leaf block drivers (drivers that access the data themselves)
- * are networking based, so they poll sockets for data and run the
- * correct coroutine.
- */
- qemu_bh_schedule(s->completion_bh);
-
- while (io_uring_peek_cqe(&s->ring, &cqes) == 0) {
- LuringAIOCB *luringcb;
- int ret;
-
- if (!cqes) {
- break;
+ if (ret < 0) {
+ /*
+ * Only writev/readv/fsync requests on regular files or host block
+ * devices are submitted. Therefore -EAGAIN is not expected but it's
+ * known to happen sometimes with Linux SCSI. Submit again and hope
+ * the request completes successfully.
+ *
+ * For more information, see:
+ * https://lore.kernel.org/io-uring/20210727165811.284510-3-axboe@kernel.dk/T/#u
+ *
+ * If the code is changed to submit other types of requests in the
+ * future, then this workaround may need to be extended to deal with
+ * genuine -EAGAIN results that should not be resubmitted
+ * immediately.
+ */
+ if (ret == -EINTR || ret == -EAGAIN) {
+ aio_add_sqe(luring_prep_sqe, req, &req->cqe_handler);
+ return;
}
-
- luringcb = io_uring_cqe_get_data(cqes);
- ret = cqes->res;
- io_uring_cqe_seen(&s->ring, cqes);
- cqes = NULL;
-
- /* Change counters one-by-one because we can be nested. */
- s->io_q.in_flight--;
- trace_luring_process_completion(s, luringcb, ret);
-
+ } else if (req->qiov) {
/* total_read is non-zero only for resubmitted read requests */
- total_bytes = ret + luringcb->total_read;
+ int total_bytes = ret + req->total_read;
- if (ret < 0) {
- /*
- * Only writev/readv/fsync requests on regular files or host block
- * devices are submitted. Therefore -EAGAIN is not expected but it's
- * known to happen sometimes with Linux SCSI. Submit again and hope
- * the request completes successfully.
- *
- * For more information, see:
- * https://lore.kernel.org/io-uring/20210727165811.284510-3-axboe@kernel.dk/T/#u
- *
- * If the code is changed to submit other types of requests in the
- * future, then this workaround may need to be extended to deal with
- * genuine -EAGAIN results that should not be resubmitted
- * immediately.
- */
- if (ret == -EINTR || ret == -EAGAIN) {
- luring_resubmit(s, luringcb);
- continue;
- }
- } else if (!luringcb->qiov) {
- goto end;
- } else if (total_bytes == luringcb->qiov->size) {
+ if (total_bytes == req->qiov->size) {
ret = 0;
- /* Only read/write */
} else {
/* Short Read/Write */
- if (luringcb->is_read) {
+ if (req->type == QEMU_AIO_READ) {
if (ret > 0) {
- luring_resubmit_short_read(s, luringcb, ret);
- continue;
- } else {
- /* Pad with zeroes */
- qemu_iovec_memset(luringcb->qiov, total_bytes, 0,
- luringcb->qiov->size - total_bytes);
- ret = 0;
+ luring_resubmit_short_read(req, ret);
+ return;
}
+
+ /* Pad with zeroes */
+ qemu_iovec_memset(req->qiov, total_bytes, 0,
+ req->qiov->size - total_bytes);
+ ret = 0;
} else {
ret = -ENOSPC;
}
}
-end:
- luringcb->ret = ret;
- qemu_iovec_destroy(&luringcb->resubmit_qiov);
-
- /*
- * If the coroutine is already entered it must be in ioq_submit()
- * and will notice luringcb->ret has been filled in when it
- * eventually runs later. Coroutines cannot be entered recursively
- * so avoid doing that!
- */
- assert(luringcb->co->ctx == s->aio_context);
- if (!qemu_coroutine_entered(luringcb->co)) {
- aio_co_wake(luringcb->co);
- }
}
- qemu_bh_cancel(s->completion_bh);
+ req->ret = ret;
+ qemu_iovec_destroy(&req->resubmit_qiov);
- defer_call_end();
-}
-
-static int ioq_submit(LuringState *s)
-{
- int ret = 0;
- LuringAIOCB *luringcb, *luringcb_next;
-
- while (s->io_q.in_queue > 0) {
- /*
- * Try to fetch sqes from the ring for requests waiting in
- * the overflow queue
- */
- QSIMPLEQ_FOREACH_SAFE(luringcb, &s->io_q.submit_queue, next,
- luringcb_next) {
- struct io_uring_sqe *sqes = io_uring_get_sqe(&s->ring);
- if (!sqes) {
- break;
- }
- /* Prep sqe for submission */
- *sqes = luringcb->sqeq;
- QSIMPLEQ_REMOVE_HEAD(&s->io_q.submit_queue, next);
- }
- ret = io_uring_submit(&s->ring);
- trace_luring_io_uring_submit(s, ret);
- /* Prevent infinite loop if submission is refused */
- if (ret <= 0) {
- if (ret == -EAGAIN || ret == -EINTR) {
- continue;
- }
- break;
- }
- s->io_q.in_flight += ret;
- s->io_q.in_queue -= ret;
- }
- s->io_q.blocked = (s->io_q.in_queue > 0);
-
- if (s->io_q.in_flight) {
- /*
- * We can try to complete something just right away if there are
- * still requests in-flight.
- */
- luring_process_completions(s);
- }
- return ret;
-}
-
-static void luring_process_completions_and_submit(LuringState *s)
-{
- luring_process_completions(s);
-
- if (s->io_q.in_queue > 0) {
- ioq_submit(s);
+ /*
+ * If the coroutine is already entered it must be in luring_co_submit() and
+ * will notice req->ret has been filled in when it eventually runs later.
+ * Coroutines cannot be entered recursively so avoid doing that!
+ */
+ if (!qemu_coroutine_entered(req->co)) {
+ aio_co_wake(req->co);
}
}
-static void qemu_luring_completion_bh(void *opaque)
+int coroutine_fn luring_co_submit(BlockDriverState *bs, int fd,
+ uint64_t offset, QEMUIOVector *qiov,
+ int type, BdrvRequestFlags flags)
{
- LuringState *s = opaque;
- luring_process_completions_and_submit(s);
-}
-
-static void qemu_luring_completion_cb(void *opaque)
-{
- LuringState *s = opaque;
- luring_process_completions_and_submit(s);
-}
-
-static bool qemu_luring_poll_cb(void *opaque)
-{
- LuringState *s = opaque;
-
- return io_uring_cq_ready(&s->ring);
-}
-
-static void qemu_luring_poll_ready(void *opaque)
-{
- LuringState *s = opaque;
-
- luring_process_completions_and_submit(s);
-}
-
-static void ioq_init(LuringQueue *io_q)
-{
- QSIMPLEQ_INIT(&io_q->submit_queue);
- io_q->in_queue = 0;
- io_q->in_flight = 0;
- io_q->blocked = false;
-}
-
-static void luring_deferred_fn(void *opaque)
-{
- LuringState *s = opaque;
- trace_luring_unplug_fn(s, s->io_q.blocked, s->io_q.in_queue,
- s->io_q.in_flight);
- if (!s->io_q.blocked && s->io_q.in_queue > 0) {
- ioq_submit(s);
- }
-}
-
-/**
- * luring_do_submit:
- * @fd: file descriptor for I/O
- * @luringcb: AIO control block
- * @s: AIO state
- * @offset: offset for request
- * @type: type of request
- *
- * Fetches sqes from ring, adds to pending queue and preps them
- *
- */
-static int luring_do_submit(int fd, LuringAIOCB *luringcb, LuringState *s,
- uint64_t offset, int type, BdrvRequestFlags flags)
-{
- int ret;
- struct io_uring_sqe *sqes = &luringcb->sqeq;
-
- switch (type) {
- case QEMU_AIO_WRITE:
-#ifdef HAVE_IO_URING_PREP_WRITEV2
- {
- int luring_flags = (flags & BDRV_REQ_FUA) ? RWF_DSYNC : 0;
- io_uring_prep_writev2(sqes, fd, luringcb->qiov->iov,
- luringcb->qiov->niov, offset, luring_flags);
- }
-#else
- assert(flags == 0);
- io_uring_prep_writev(sqes, fd, luringcb->qiov->iov,
- luringcb->qiov->niov, offset);
-#endif
- break;
- case QEMU_AIO_ZONE_APPEND:
- io_uring_prep_writev(sqes, fd, luringcb->qiov->iov,
- luringcb->qiov->niov, offset);
- break;
- case QEMU_AIO_READ:
- io_uring_prep_readv(sqes, fd, luringcb->qiov->iov,
- luringcb->qiov->niov, offset);
- break;
- case QEMU_AIO_FLUSH:
- io_uring_prep_fsync(sqes, fd, IORING_FSYNC_DATASYNC);
- break;
- default:
- fprintf(stderr, "%s: invalid AIO request type, aborting 0x%x.\n",
- __func__, type);
- abort();
- }
- io_uring_sqe_set_data(sqes, luringcb);
-
- QSIMPLEQ_INSERT_TAIL(&s->io_q.submit_queue, luringcb, next);
- s->io_q.in_queue++;
- trace_luring_do_submit(s, s->io_q.blocked, s->io_q.in_queue,
- s->io_q.in_flight);
- if (!s->io_q.blocked) {
- if (s->io_q.in_flight + s->io_q.in_queue >= MAX_ENTRIES) {
- ret = ioq_submit(s);
- trace_luring_do_submit_done(s, ret);
- return ret;
- }
-
- defer_call(luring_deferred_fn, s);
- }
- return 0;
-}
-
-int coroutine_fn luring_co_submit(BlockDriverState *bs, int fd, uint64_t offset,
- QEMUIOVector *qiov, int type,
- BdrvRequestFlags flags)
-{
- int ret;
- AioContext *ctx = qemu_get_current_aio_context();
- LuringState *s = aio_get_linux_io_uring(ctx);
- LuringAIOCB luringcb = {
+ LuringRequest req = {
.co = qemu_coroutine_self(),
- .ret = -EINPROGRESS,
.qiov = qiov,
- .is_read = (type == QEMU_AIO_READ),
+ .ret = -EINPROGRESS,
+ .type = type,
+ .fd = fd,
+ .offset = offset,
+ .flags = flags,
};
- trace_luring_co_submit(bs, s, &luringcb, fd, offset, qiov ? qiov->size : 0,
- type);
- ret = luring_do_submit(fd, &luringcb, s, offset, type, flags);
- if (ret < 0) {
- return ret;
- }
+ req.cqe_handler.cb = luring_cqe_handler;
- if (luringcb.ret == -EINPROGRESS) {
+ trace_luring_co_submit(bs, &req, fd, offset, qiov ? qiov->size : 0, type);
+ aio_add_sqe(luring_prep_sqe, &req, &req.cqe_handler);
+
+ if (req.ret == -EINPROGRESS) {
qemu_coroutine_yield();
}
- return luringcb.ret;
-}
-
-void luring_detach_aio_context(LuringState *s, AioContext *old_context)
-{
- aio_set_fd_handler(old_context, s->ring.ring_fd,
- NULL, NULL, NULL, NULL, s);
- qemu_bh_delete(s->completion_bh);
- s->aio_context = NULL;
-}
-
-void luring_attach_aio_context(LuringState *s, AioContext *new_context)
-{
- s->aio_context = new_context;
- s->completion_bh = aio_bh_new(new_context, qemu_luring_completion_bh, s);
- aio_set_fd_handler(s->aio_context, s->ring.ring_fd,
- qemu_luring_completion_cb, NULL,
- qemu_luring_poll_cb, qemu_luring_poll_ready, s);
-}
-
-LuringState *luring_init(Error **errp)
-{
- int rc;
- LuringState *s = g_new0(LuringState, 1);
- struct io_uring *ring = &s->ring;
-
- trace_luring_init_state(s, sizeof(*s));
-
- rc = io_uring_queue_init(MAX_ENTRIES, ring, 0);
- if (rc < 0) {
- error_setg_errno(errp, -rc, "failed to init linux io_uring ring");
- g_free(s);
- return NULL;
- }
-
- ioq_init(&s->io_q);
- return s;
-
-}
-
-void luring_cleanup(LuringState *s)
-{
- io_uring_queue_exit(&s->ring);
- trace_luring_cleanup_state(s);
- g_free(s);
+ return req.ret;
}
bool luring_has_fua(void)
diff --git a/stubs/io_uring.c b/stubs/io_uring.c
deleted file mode 100644
index 622d1e4648..0000000000
--- a/stubs/io_uring.c
+++ /dev/null
@@ -1,32 +0,0 @@
-/*
- * Linux io_uring support.
- *
- * Copyright (C) 2009 IBM, Corp.
- * Copyright (C) 2009 Red Hat, Inc.
- *
- * This work is licensed under the terms of the GNU GPL, version 2 or later.
- * See the COPYING file in the top-level directory.
- */
-#include "qemu/osdep.h"
-#include "block/aio.h"
-#include "block/raw-aio.h"
-
-void luring_detach_aio_context(LuringState *s, AioContext *old_context)
-{
- abort();
-}
-
-void luring_attach_aio_context(LuringState *s, AioContext *new_context)
-{
- abort();
-}
-
-LuringState *luring_init(Error **errp)
-{
- abort();
-}
-
-void luring_cleanup(LuringState *s)
-{
- abort();
-}
diff --git a/util/async.c b/util/async.c
index 2bb7e1f3c1..6a880714d9 100644
--- a/util/async.c
+++ b/util/async.c
@@ -383,14 +383,6 @@ aio_ctx_finalize(GSource *source)
}
#endif
-#ifdef CONFIG_LINUX_IO_URING
- if (ctx->linux_io_uring) {
- luring_detach_aio_context(ctx->linux_io_uring, ctx);
- luring_cleanup(ctx->linux_io_uring);
- ctx->linux_io_uring = NULL;
- }
-#endif
-
assert(QSLIST_EMPTY(&ctx->scheduled_coroutines));
qemu_bh_delete(ctx->co_schedule_bh);
@@ -465,29 +457,6 @@ LinuxAioState *aio_get_linux_aio(AioContext *ctx)
}
#endif
-#ifdef CONFIG_LINUX_IO_URING
-LuringState *aio_setup_linux_io_uring(AioContext *ctx, Error **errp)
-{
- if (ctx->linux_io_uring) {
- return ctx->linux_io_uring;
- }
-
- ctx->linux_io_uring = luring_init(errp);
- if (!ctx->linux_io_uring) {
- return NULL;
- }
-
- luring_attach_aio_context(ctx->linux_io_uring, ctx);
- return ctx->linux_io_uring;
-}
-
-LuringState *aio_get_linux_io_uring(AioContext *ctx)
-{
- assert(ctx->linux_io_uring);
- return ctx->linux_io_uring;
-}
-#endif
-
void aio_notify(AioContext *ctx)
{
/*
@@ -611,10 +580,6 @@ AioContext *aio_context_new(Error **errp)
ctx->linux_aio = NULL;
#endif
-#ifdef CONFIG_LINUX_IO_URING
- ctx->linux_io_uring = NULL;
-#endif
-
ctx->thread_pool = NULL;
qemu_rec_mutex_init(&ctx->lock);
timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c
index 9ed02597d6..28b93c8ab9 100644
--- a/util/fdmon-io_uring.c
+++ b/util/fdmon-io_uring.c
@@ -49,6 +49,7 @@
#include "qemu/defer-call.h"
#include "qemu/rcu_queue.h"
#include "aio-posix.h"
+#include "trace.h"
enum {
FDMON_IO_URING_ENTRIES = 128, /* sq/cq ring size */
@@ -177,6 +178,9 @@ static void fdmon_io_uring_add_sqe(AioContext *ctx,
prep_sqe(sqe, opaque);
io_uring_sqe_set_data(sqe, cqe_handler);
+
+ trace_fdmon_io_uring_add_sqe(ctx, opaque, sqe->opcode, sqe->fd, sqe->off,
+ cqe_handler);
}
static void fdmon_special_cqe_handler(CqeHandler *cqe_handler)
@@ -304,6 +308,8 @@ static void cqe_handler_bh(void *opaque)
QSIMPLEQ_REMOVE_HEAD(ready_list, next);
+ trace_fdmon_io_uring_cqe_handler(ctx, cqe_handler,
+ cqe_handler->cqe.res);
cqe_handler->cb(cqe_handler);
}
diff --git a/block/trace-events b/block/trace-events
index 8e789e1f12..c9b4736ff8 100644
--- a/block/trace-events
+++ b/block/trace-events
@@ -62,15 +62,9 @@ qmp_block_stream(void *bs) "bs %p"
file_paio_submit(void *acb, void *opaque, int64_t offset, int count, int type) "acb %p opaque %p offset %"PRId64" count %d type %d"
# io_uring.c
-luring_init_state(void *s, size_t size) "s %p size %zu"
-luring_cleanup_state(void *s) "%p freed"
-luring_unplug_fn(void *s, int blocked, int queued, int inflight) "LuringState %p blocked %d queued %d inflight %d"
-luring_do_submit(void *s, int blocked, int queued, int inflight) "LuringState %p blocked %d queued %d inflight %d"
-luring_do_submit_done(void *s, int ret) "LuringState %p submitted to kernel %d"
-luring_co_submit(void *bs, void *s, void *luringcb, int fd, uint64_t offset, size_t nbytes, int type) "bs %p s %p luringcb %p fd %d offset %" PRId64 " nbytes %zd type %d"
-luring_process_completion(void *s, void *aiocb, int ret) "LuringState %p luringcb %p ret %d"
-luring_io_uring_submit(void *s, int ret) "LuringState %p ret %d"
-luring_resubmit_short_read(void *s, void *luringcb, int nread) "LuringState %p luringcb %p nread %d"
+luring_cqe_handler(void *req, int ret) "req %p ret %d"
+luring_co_submit(void *bs, void *req, int fd, uint64_t offset, size_t nbytes, int type) "bs %p req %p fd %d offset %" PRId64 " nbytes %zd type %d"
+luring_resubmit_short_read(void *req, int nread) "req %p nread %d"
# qcow2.c
qcow2_add_task(void *co, void *bs, void *pool, const char *action, int cluster_type, uint64_t host_offset, uint64_t offset, uint64_t bytes, void *qiov, size_t qiov_offset) "co %p bs %p pool %p: %s: cluster_type %d file_cluster_offset %" PRIu64 " offset %" PRIu64 " bytes %" PRIu64 " qiov %p qiov_offset %zu"
diff --git a/stubs/meson.build b/stubs/meson.build
index cef046e685..93aa90c817 100644
--- a/stubs/meson.build
+++ b/stubs/meson.build
@@ -32,9 +32,6 @@ if have_block or have_ga
stub_ss.add(files('cpus-virtual-clock.c'))
stub_ss.add(files('icount.c'))
stub_ss.add(files('graph-lock.c'))
- if linux_io_uring.found()
- stub_ss.add(files('io_uring.c'))
- endif
if libaio.found()
stub_ss.add(files('linux-aio.c'))
endif
diff --git a/util/trace-events b/util/trace-events
index bd8f25fb59..540d662507 100644
--- a/util/trace-events
+++ b/util/trace-events
@@ -24,6 +24,10 @@ buffer_move_empty(const char *buf, size_t len, const char *from) "%s: %zd bytes
buffer_move(const char *buf, size_t len, const char *from) "%s: %zd bytes from %s"
buffer_free(const char *buf, size_t len) "%s: capacity %zd"
+# fdmon-io_uring.c
+fdmon_io_uring_add_sqe(void *ctx, void *opaque, int opcode, int fd, uint64_t off, void *cqe_handler) "ctx %p opaque %p opcode %d fd %d off %"PRId64" cqe_handler %p"
+fdmon_io_uring_cqe_handler(void *ctx, void *cqe_handler, int cqe_res) "ctx %p cqe_handler %p cqe_res %d"
+
# filemonitor-inotify.c
qemu_file_monitor_add_watch(void *mon, const char *dirpath, const char *filename, void *cb, void *opaque, int64_t id) "File monitor %p add watch dir='%s' file='%s' cb=%p opaque=%p id=%" PRId64
qemu_file_monitor_remove_watch(void *mon, const char *dirpath, int64_t id) "File monitor %p remove watch dir='%s' id=%" PRId64
--
2.51.0
^ permalink raw reply related [flat|nested] 25+ messages in thread* [PATCH v4 12/12] block/io_uring: use non-vectored read/write when possible
2025-09-10 17:56 [PATCH v4 00/12] aio: add the aio_add_sqe() io_uring API Stefan Hajnoczi
` (10 preceding siblings ...)
2025-09-10 17:57 ` [PATCH v4 11/12] block/io_uring: use aio_add_sqe() Stefan Hajnoczi
@ 2025-09-10 17:57 ` Stefan Hajnoczi
2025-10-10 16:33 ` Kevin Wolf
11 siblings, 1 reply; 25+ messages in thread
From: Stefan Hajnoczi @ 2025-09-10 17:57 UTC (permalink / raw)
To: qemu-devel
Cc: Aarushi Mehta, Fam Zheng, Stefano Garzarella, Hanna Czenczek,
eblake, Stefan Hajnoczi, Kevin Wolf, qemu-block, hibriansong,
Stefan Weil, Paolo Bonzini
The io_uring_prep_readv2/writev2() man pages recommend using the
non-vectored read/write operations when possible for performance
reasons.
I didn't measure a significant difference but it doesn't hurt to have
this optimization in place.
Suggested-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
block/io_uring.c | 29 ++++++++++++++++++++++++-----
1 file changed, 24 insertions(+), 5 deletions(-)
diff --git a/block/io_uring.c b/block/io_uring.c
index dd930ee57e..bbefbddcc0 100644
--- a/block/io_uring.c
+++ b/block/io_uring.c
@@ -49,12 +49,24 @@ static void luring_prep_sqe(struct io_uring_sqe *sqe, void *opaque)
#ifdef HAVE_IO_URING_PREP_WRITEV2
{
int luring_flags = (flags & BDRV_REQ_FUA) ? RWF_DSYNC : 0;
- io_uring_prep_writev2(sqe, fd, qiov->iov,
- qiov->niov, offset, luring_flags);
+ if (luring_flags != 0 || qiov->niov > 1) {
+ io_uring_prep_writev2(sqe, fd, qiov->iov,
+ qiov->niov, offset, luring_flags);
+ } else {
+ /* The man page says non-vectored is faster than vectored */
+ struct iovec *iov = qiov->iov;
+ io_uring_prep_write(sqe, fd, iov->iov_base, iov->iov_len, offset);
+ }
}
#else
assert(flags == 0);
- io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset);
+ if (qiov->niov > 1) {
+ io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset);
+ } else {
+ /* The man page says non-vectored is faster than vectored */
+ struct iovec *iov = qiov->iov;
+ io_uring_prep_write(sqe, fd, iov->iov_base, iov->iov_len, offset);
+ }
#endif
break;
case QEMU_AIO_ZONE_APPEND:
@@ -65,8 +77,15 @@ static void luring_prep_sqe(struct io_uring_sqe *sqe, void *opaque)
if (req->resubmit_qiov.iov != NULL) {
qiov = &req->resubmit_qiov;
}
- io_uring_prep_readv(sqe, fd, qiov->iov, qiov->niov,
- offset + req->total_read);
+ if (qiov->niov > 1) {
+ io_uring_prep_readv(sqe, fd, qiov->iov, qiov->niov,
+ offset + req->total_read);
+ } else {
+ /* The man page says non-vectored is faster than vectored */
+ struct iovec *iov = qiov->iov;
+ io_uring_prep_read(sqe, fd, iov->iov_base, iov->iov_len,
+ offset + req->total_read);
+ }
break;
}
case QEMU_AIO_FLUSH:
--
2.51.0
^ permalink raw reply related [flat|nested] 25+ messages in thread* Re: [PATCH v4 12/12] block/io_uring: use non-vectored read/write when possible
2025-09-10 17:57 ` [PATCH v4 12/12] block/io_uring: use non-vectored read/write when possible Stefan Hajnoczi
@ 2025-10-10 16:33 ` Kevin Wolf
0 siblings, 0 replies; 25+ messages in thread
From: Kevin Wolf @ 2025-10-10 16:33 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: qemu-devel, Aarushi Mehta, Fam Zheng, Stefano Garzarella,
Hanna Czenczek, eblake, qemu-block, hibriansong, Stefan Weil,
Paolo Bonzini
Am 10.09.2025 um 19:57 hat Stefan Hajnoczi geschrieben:
> The io_uring_prep_readv2/writev2() man pages recommend using the
> non-vectored read/write operations when possible for performance
> reasons.
>
> I didn't measure a significant difference but it doesn't hurt to have
> this optimization in place.
>
> Suggested-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> block/io_uring.c | 29 ++++++++++++++++++++++++-----
> 1 file changed, 24 insertions(+), 5 deletions(-)
>
> diff --git a/block/io_uring.c b/block/io_uring.c
> index dd930ee57e..bbefbddcc0 100644
> --- a/block/io_uring.c
> +++ b/block/io_uring.c
> @@ -49,12 +49,24 @@ static void luring_prep_sqe(struct io_uring_sqe *sqe, void *opaque)
> #ifdef HAVE_IO_URING_PREP_WRITEV2
> {
> int luring_flags = (flags & BDRV_REQ_FUA) ? RWF_DSYNC : 0;
> - io_uring_prep_writev2(sqe, fd, qiov->iov,
> - qiov->niov, offset, luring_flags);
> + if (luring_flags != 0 || qiov->niov > 1) {
> + io_uring_prep_writev2(sqe, fd, qiov->iov,
> + qiov->niov, offset, luring_flags);
> + } else {
> + /* The man page says non-vectored is faster than vectored */
> + struct iovec *iov = qiov->iov;
> + io_uring_prep_write(sqe, fd, iov->iov_base, iov->iov_len, offset);
> + }
> }
> #else
> assert(flags == 0);
> - io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset);
> + if (qiov->niov > 1) {
> + io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset);
> + } else {
> + /* The man page says non-vectored is faster than vectored */
> + struct iovec *iov = qiov->iov;
> + io_uring_prep_write(sqe, fd, iov->iov_base, iov->iov_len, offset);
> + }
> #endif
We have a lot of duplication in this now. Let's use the #ifdef a little
more locally:
{
int luring_flags = (flags & BDRV_REQ_FUA) ? RWF_DSYNC : 0;
if (luring_flags != 0 || qiov->niov > 1) {
#ifdef HAVE_IO_URING_PREP_WRITEV2
io_uring_prep_writev2(sqe, fd, qiov->iov,
qiov->niov, offset, luring_flags);
#else
assert(luring_flags == 0);
io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset);
#endif
} else {
/* The man page says non-vectored is faster than vectored */
struct iovec *iov = qiov->iov;
io_uring_prep_write(sqe, fd, iov->iov_base, iov->iov_len, offset);
}
}
Kevin
^ permalink raw reply [flat|nested] 25+ messages in thread