[Qemu-devel] [RFC 03/13] aio: stop using .io_flush()

[Stefan Hajnoczi <stefanha@redhat.com>]

Now that bdrv_drain_all() checks that requests are pending before
calling qemu_aio_wait(), it is no longer necessary to call .io_flush()
handlers.

Behavior of aio_poll() changes as follows:

.io_flush() is no longer invoked and file descriptors are *always*
monitored.  Previously returning 0 from .io_flush() would skip this file
descriptor.

Due to these changes it is essential to check that requests are pending
before calling qemu_aio_wait().  Failure to do so means we block, for
example, waiting for an idle iSCSI socket to become readable when there
are no requests.  Currently all qemu_aio_wait()/aio_poll() callers check
before calling.

The next patches will remove .io_flush() handler code until we can
finally drop the io_flush arguments to aio_set_fd_handler() and friends.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 aio-posix.c | 24 ++----------------------
 aio-win32.c | 23 ++---------------------
 2 files changed, 4 insertions(+), 43 deletions(-)

diff --git a/aio-posix.c b/aio-posix.c
index b68eccd..569e603 100644
--- a/aio-posix.c
+++ b/aio-posix.c
@@ -23,7 +23,6 @@ struct AioHandler
     GPollFD pfd;
     IOHandler *io_read;
     IOHandler *io_write;
-    AioFlushHandler *io_flush;
     int deleted;
     int pollfds_idx;
     void *opaque;
@@ -84,7 +83,6 @@ void aio_set_fd_handler(AioContext *ctx,
         /* Update handler with latest information */
         node->io_read = io_read;
         node->io_write = io_write;
-        node->io_flush = io_flush;
         node->opaque = opaque;
         node->pollfds_idx = -1;
 
@@ -173,7 +171,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
 {
     AioHandler *node;
     int ret;
-    bool busy, progress;
+    bool progress;
 
     progress = false;
 
@@ -200,20 +198,8 @@ bool aio_poll(AioContext *ctx, bool blocking)
     g_array_set_size(ctx->pollfds, 0);
 
     /* fill pollfds */
-    busy = false;
     QLIST_FOREACH(node, &ctx->aio_handlers, node) {
         node->pollfds_idx = -1;
-
-        /* If there aren't pending AIO operations, don't invoke callbacks.
-         * Otherwise, if there are no AIO requests, qemu_aio_wait() would
-         * wait indefinitely.
-         */
-        if (!node->deleted && node->io_flush) {
-            if (node->io_flush(node->opaque) == 0) {
-                continue;
-            }
-            busy = true;
-        }
         if (!node->deleted && node->pfd.events) {
             GPollFD pfd = {
                 .fd = node->pfd.fd,
@@ -226,11 +212,6 @@ bool aio_poll(AioContext *ctx, bool blocking)
 
     ctx->walking_handlers--;
 
-    /* No AIO operations?  Get us out of here */
-    if (!busy) {
-        return progress;
-    }
-
     /* wait until next event */
     ret = g_poll((GPollFD *)ctx->pollfds->data,
                  ctx->pollfds->len,
@@ -250,6 +231,5 @@ bool aio_poll(AioContext *ctx, bool blocking)
         }
     }
 
-    assert(progress || busy);
-    return true;
+    return progress;
 }
diff --git a/aio-win32.c b/aio-win32.c
index 38723bf..0980d08 100644
--- a/aio-win32.c
+++ b/aio-win32.c
@@ -23,7 +23,6 @@
 struct AioHandler {
     EventNotifier *e;
     EventNotifierHandler *io_notify;
-    AioFlushEventNotifierHandler *io_flush;
     GPollFD pfd;
     int deleted;
     QLIST_ENTRY(AioHandler) node;
@@ -73,7 +72,6 @@ void aio_set_event_notifier(AioContext *ctx,
         }
         /* Update handler with latest information */
         node->io_notify = io_notify;
-        node->io_flush = io_flush;
     }
 
     aio_notify(ctx);
@@ -96,7 +94,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
 {
     AioHandler *node;
     HANDLE events[MAXIMUM_WAIT_OBJECTS + 1];
-    bool busy, progress;
+    bool progress;
     int count;
 
     progress = false;
@@ -147,19 +145,8 @@ bool aio_poll(AioContext *ctx, bool blocking)
     ctx->walking_handlers++;
 
     /* fill fd sets */
-    busy = false;
     count = 0;
     QLIST_FOREACH(node, &ctx->aio_handlers, node) {
-        /* If there aren't pending AIO operations, don't invoke callbacks.
-         * Otherwise, if there are no AIO requests, qemu_aio_wait() would
-         * wait indefinitely.
-         */
-        if (!node->deleted && node->io_flush) {
-            if (node->io_flush(node->e) == 0) {
-                continue;
-            }
-            busy = true;
-        }
         if (!node->deleted && node->io_notify) {
             events[count++] = event_notifier_get_handle(node->e);
         }
@@ -167,11 +154,6 @@ bool aio_poll(AioContext *ctx, bool blocking)
 
     ctx->walking_handlers--;
 
-    /* No AIO operations?  Get us out of here */
-    if (!busy) {
-        return progress;
-    }
-
     /* wait until next event */
     while (count > 0) {
         int timeout = blocking ? INFINITE : 0;
@@ -214,6 +196,5 @@ bool aio_poll(AioContext *ctx, bool blocking)
         events[ret - WAIT_OBJECT_0] = events[--count];
     }
 
-    assert(progress || busy);
-    return true;
+    return progress;
 }
-- 
1.8.1.4