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aio: stop using .io_flush()

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Now that aio_poll() users check their termination condition themselves,
it is no longer necessary to call .io_flush() handlers.

The behavior of aio_poll() changes as follows:

1. .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 this change 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.

2. aio_poll() now returns true if progress was made (BH or fd handlers
executed) and false otherwise.  Previously it would return true whenever
'busy', which means that .io_flush() returned true.  The 'busy' concept
no longer exists so just progress is returned.

Due to this change we need to update tests/test-aio.c which asserts
aio_poll() return values.  Note that QEMU doesn't actually rely on these
return values so only tests/test-aio.c cares.

Note that ctx->notifier, the EventNotifier fd used for aio_notify(), is
now handled as a special case.  This is a little ugly but maintains
aio_poll() semantics, i.e. aio_notify() does not count as 'progress' and
aio_poll() avoids blocking when the user has not set any fd handlers yet.

Patches after this remove .io_flush() handler code until we can finally
drop the io_flush arguments to aio_set_fd_handler() and friends.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2013-04-11 16:56:50 +02:00
parent 35ecde2601
commit 164a101f28
3 changed files with 28 additions and 45 deletions
Download patch file Download diff file Expand all files Collapse all files

10
tests/test-aio.c
View file

@ -254,7 +254,7 @@ static void test_wait_event_notifier(void)
EventNotifierTestData data = { .n = 0, .active = 1 };
event_notifier_init(&data.e, false);
aio_set_event_notifier(ctx, &data.e, event_ready_cb, event_active_cb);
g_assert(aio_poll(ctx, false));
g_assert(!aio_poll(ctx, false));
g_assert_cmpint(data.n, ==, 0);
g_assert_cmpint(data.active, ==, 1);
@ -279,7 +279,7 @@ static void test_flush_event_notifier(void)
EventNotifierTestData data = { .n = 0, .active = 10, .auto_set = true };
event_notifier_init(&data.e, false);
aio_set_event_notifier(ctx, &data.e, event_ready_cb, event_active_cb);
g_assert(aio_poll(ctx, false));
g_assert(!aio_poll(ctx, false));
g_assert_cmpint(data.n, ==, 0);
g_assert_cmpint(data.active, ==, 10);
@ -313,7 +313,7 @@ static void test_wait_event_notifier_noflush(void)
/* Until there is an active descriptor, aio_poll may or may not call
* event_ready_cb. Still, it must not block. */
event_notifier_set(&data.e);
g_assert(!aio_poll(ctx, true));
g_assert(aio_poll(ctx, true));
data.n = 0;
/* An active event notifier forces aio_poll to look at EventNotifiers. */
@ -323,13 +323,13 @@ static void test_wait_event_notifier_noflush(void)
event_notifier_set(&data.e);
g_assert(aio_poll(ctx, false));
g_assert_cmpint(data.n, ==, 1);
g_assert(aio_poll(ctx, false));
g_assert(!aio_poll(ctx, false));
g_assert_cmpint(data.n, ==, 1);
event_notifier_set(&data.e);
g_assert(aio_poll(ctx, false));
g_assert_cmpint(data.n, ==, 2);
g_assert(aio_poll(ctx, false));
g_assert(!aio_poll(ctx, false));
g_assert_cmpint(data.n, ==, 2);
event_notifier_set(&dummy.e);