Re: [PATCH 1/3] aio-posix: treat io_uring setup failure as fatal

[Kevin Wolf <kwolf@redhat.com>]

Am 01.04.2025 um 16:27 hat Stefan Hajnoczi geschrieben:
> In the early days of io_uring it was possible for io_uring_setup(2) to
> fail due to exhausting RLIMIT_MEMLOCK. QEMU's solution was to fall back
> to epoll(7) or ppoll(2) when io_uring could not be used in an
> AioContext.
> 
> Nowadays io_uring memory is accounted differently so io_uring_setup(2)
> won't fail. Treat failure as a fatal error. Keep it simple: io_uring is
> available if and only if CONFIG_LINUX_IO_URING is defined.
> 
> Upcoming features that rely on io_uring won't need to handle the case
> where a subset of AioContexts lacks io_uring. This will simplify the
> aio_add_sqe() API introduced in the next commit.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

While making failure to set up io_uring for an AioContext a hard error
feels fine to me, I feel a bit uneasy about having fatal errors like
this in functions that aren't only called during startup. This function
is also called when adding an iothread object at runtime. The failure
mode that I would expect there is that object-add returns an error, not
that the whole QEMU process exits.

Kevin