[RFC 1/5] io_uring/cmd: expose iowq to cmds

Pavel Begunkov
2024-08-14T10:45:27Z

When an io_uring request needs blocking context we offload it to the
io_uring's thread pool called io-wq. We can get there off ->uring_cmd
by returning -EAGAIN, but there is no straightforward way of doing that
from an asynchronous callback. Add a helper that would transfer a
command to a blocking context.

Note, we do an extra hop via task_work before io_queue_iowq(), that's a
limitation of io_uring infra we have that can likely be lifted later
if that would ever become a problem.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
include/linux/io_uring/cmd.h | 6 ++++++
io_uring/io_uring.c | 11 +++++++++++
io_uring/io_uring.h | 1 +
io_uring/uring_cmd.c | 7 +++++++
4 files changed, 25 insertions(+)

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index 447fbfd32215..86ceb3383e49 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -48,6 +48,9 @@ void __io_uring_cmd_do_in_task(struct io_uring_cmd *ioucmd,
void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd,
unsigned int issue_flags);

+/* Execute the request from a blocking context */
+void io_uring_cmd_issue_blocking(struct io_uring_cmd *ioucmd);
+
#else
static inline int io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw,
struct iov_iter *iter, void *ioucmd)
@@ -67,6 +70,9 @@ static inline void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd,
unsigned int issue_flags)
{
}
+static inline void io_uring_cmd_issue_blocking(struct io_uring_cmd *ioucmd)
+{
+}
#endif

/*
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 3942db160f18..da819018088d 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -533,6 +533,17 @@ static void io_queue_iowq(struct io_kiocb *req)
io_queue_linked_timeout(link);
}

+static void io_req_queue_iowq_tw(struct io_kiocb *req, struct io_tw_state *ts)
+{
+ io_queue_iowq(req);
+}
+
+void io_req_queue_iowq(struct io_kiocb *req)
+{
+ req->io_task_work.func = io_req_queue_iowq_tw;
+ io_req_task_work_add(req);
+}
+
static __cold void io_queue_deferred(struct io_ring_ctx *ctx)
{
while (!list_empty(&ctx->defer_list)) {
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index c2acf6180845..2896587a5221 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -90,6 +90,7 @@ int io_uring_alloc_task_context(struct task_struct *task,

int io_ring_add_registered_file(struct io_uring_task *tctx, struct file *file,
int start, int end);
+void io_req_queue_iowq(struct io_kiocb *req);

int io_poll_issue(struct io_kiocb *req, struct io_tw_state *ts);
int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr);
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index 8391c7c7c1ec..39c3c816ec78 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -277,6 +277,13 @@ int io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw,
}
EXPORT_SYMBOL_GPL(io_uring_cmd_import_fixed);

+void io_uring_cmd_issue_blocking(struct io_uring_cmd *ioucmd)
+{
+ struct io_kiocb *req = cmd_to_io_kiocb(ioucmd);
+
+ io_req_queue_iowq(req);
+}
+
static inline int io_uring_cmd_getsockopt(struct socket *sock,
struct io_uring_cmd *cmd,
unsigned int issue_flags)
--
2.45.2