Re: [PATCH v6 00/15] aio: add the aio_add_sqe() io_uring API

[Kevin Wolf <kwolf@redhat.com>]

Am 13.11.2025 um 09:27 hat Michael Tokarev geschrieben:
> On 11/4/25 05:29, Stefan Hajnoczi wrote:
> ..
> > This patch series contains io_uring improvements:
> > 
> > 1. Support the glib event loop in fdmon-io_uring.
> >     - aio-posix: fix race between io_uring CQE and AioHandler deletion
> >     - aio-posix: keep polling enabled with fdmon-io_uring.c
> >     - tests/unit: skip test-nested-aio-poll with io_uring
> >     - aio-posix: integrate fdmon into glib event loop
> > 
> > 2. Enable fdmon-io_uring on hosts where io_uring is available at runtime.
> >     Otherwise continue using ppoll(2) or epoll(7).
> >     - aio: remove aio_context_use_g_source()
> > 
> > 3. Add the new aio_add_sqe() API for submitting io_uring requests in the QEMU
> >     event loop.
> >     - aio: free AioContext when aio_context_new() fails
> >     - aio: add errp argument to aio_context_setup()
> >     - aio-posix: gracefully handle io_uring_queue_init() failure
> >     - aio-posix: add aio_add_sqe() API for user-defined io_uring requests
> >     - aio-posix: avoid EventNotifier for cqe_handler_bh
> > 
> > 4. Use aio_add_sqe() in block/io_uring.c instead of creating a dedicated
> >     io_uring context for --blockdev aio=io_uring. This simplifies the code,
> >     reduces the number of file descriptors, and demonstrates the aio_add_sqe()
> >     API.
> >     - block/io_uring: use aio_add_sqe()
> >     - block/io_uring: use non-vectored read/write when possible
> > 
> > The highlight is aio_add_sqe(), which is needed for the FUSE-over-io_uring
> > Google Summer of Code project and other future QEMU features that natively use
> > Linux io_uring functionality.
> ..> Stefan Hajnoczi (15):
> >    aio-posix: fix race between io_uring CQE and AioHandler deletion
> >    aio-posix: fix fdmon-io_uring.c timeout stack variable lifetime
> >    aio-posix: fix spurious return from ->wait() due to signals
> >    aio-posix: keep polling enabled with fdmon-io_uring.c
> >    tests/unit: skip test-nested-aio-poll with io_uring
> >    aio-posix: integrate fdmon into glib event loop
> >    aio: remove aio_context_use_g_source()
> >    aio: free AioContext when aio_context_new() fails
> >    aio: add errp argument to aio_context_setup()
> >    aio-posix: gracefully handle io_uring_queue_init() failure
> >    aio-posix: unindent fdmon_io_uring_destroy()
> >    aio-posix: add fdmon_ops->dispatch()
> >    aio-posix: add aio_add_sqe() API for user-defined io_uring requests
> >    block/io_uring: use aio_add_sqe()
> >    block/io_uring: use non-vectored read/write when possible
> 
> Is there anything in there which should go to qemu-stable?
> 
> From the descriptions of a few changes it feels like something should.

fdmon-io_uring has effectively been dead code since commit ba607ca (and
until patch 7 in this series). The commit message of that commit makes
it sounds like there are cases where GSource is not enabled, but there
really aren't.

You may want to pick patch 2 anyway because it's a use after free and
may effectively hang QEMU (by using far too large timeouts), but from
what I can tell, without downstream code changes, you won't ever run
this code in relevant stable releases. QEMU 5.0 was the only release
that had it enabled before.

Kevin