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aio-posix: support userspace polling of fd monitoring

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Unlike ppoll(2) and epoll(7), Linux io_uring completions can be polled
from userspace.  Previously userspace polling was only allowed when all
AioHandler's had an ->io_poll() callback.  This prevented starvation of
fds by userspace pollable handlers.

Add the FDMonOps->need_wait() callback that enables userspace polling
even when some AioHandlers lack ->io_poll().

For example, it's now possible to do userspace polling when a TCP/IP
socket is monitored thanks to Linux io_uring.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Link: https://lore.kernel.org/r/20200305170806.1313245-7-stefanha@redhat.com
Message-Id: <20200305170806.1313245-7-stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi
2020-03-05 17:08:05 +00:00
parent 73fd282e7b
commit aa38e19f05
5 changed files with 35 additions and 3 deletions
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6
util/fdmon-io_uring.c
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@ -288,9 +288,15 @@ static int fdmon_io_uring_wait(AioContext *ctx, AioHandlerList *ready_list,
return process_cq_ring(ctx, ready_list);
}
static bool fdmon_io_uring_need_wait(AioContext *ctx)
{
return io_uring_cq_ready(&ctx->fdmon_io_uring);
}
static const FDMonOps fdmon_io_uring_ops = {
.update = fdmon_io_uring_update,
.wait = fdmon_io_uring_wait,
.need_wait = fdmon_io_uring_need_wait,
};
bool fdmon_io_uring_setup(AioContext *ctx)