On Wed, May 28, 2025 at 03:09:06PM -0400, Stefan Hajnoczi wrote: > The io_uring(7) file descriptor monitor cannot enter polling mode > because it needs to submit a POLL_ADD SQE every time a file descriptor > becomes active. Submitting SQEs only happens in FDMonOps->wait() outside > of polling mode. > > Fix this using the multi-shot mechanism introduced in Linux 5.13 and > liburing 2.1. Stable and enterprise Linux distros ship 5.14+ as of March > 2025, so it is safe to require this. Note that fdmon-io_uring is > currently not enabled at runtime and is not essential, so QEMU can still > be built without it on older hosts. > > In multi-shot mode, a POLL_ADD SQE remains active until canceled with > POLL_REMOVE. This avoids the need to submit a new SQE every time a file > descriptor becomes active. > > When POLL_REMOVE is processed by the host kernel, the multi-shot > POLL_ADD operation completes with -ECANCELED. Adjust the code slightly > to take this into account. > > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> > ---
Reviewed-by: Eric Blake <ebl...@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. Virtualization: qemu.org | libguestfs.org
