Re: [PATCH v2] linux-aio: add IO_CMD_FDSYNC command support

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Mar 12, 2024 at 07:07:04PM +0530, Prasad Pandit wrote:
> Hello,
> 
> On Tue, 12 Mar 2024 at 15:15, Kevin Wolf <kwolf@redhat.com> wrote:
> > Am 11.03.2024 um 20:36 hat Stefan Hajnoczi geschrieben:
> > > > > That can be avoided with a variable that keeps track of whether -EINVAL was seen before and skips Linux AIO in that
> > > > > case.
> > > > >
> > > > > Fallback should be very rare, so I don't think it needs to be optimized:
> > You're right. I missed that io_submit() returns failure only if the
> > first request in the queue is invalid, and returns a "short submission"
> > for errors in later entries.
> 
> ===
> +bool laio_has_fdsync(int fd)
> +{
> +    AioContext *ctx = qemu_get_current_aio_context();
> +    struct qemu_laiocb cb = {
> +        .co         = qemu_coroutine_self(),
> +        .ctx        = aio_get_linux_aio(ctx),
> +    };
> +    struct iocb *iocbs[] = {&cb.iocb, NULL};
> +
> +    /* check if host kernel supports IO_CMD_FDSYNC */
> +    io_prep_fdsync(&cb.iocb, fd);
> +    int ret = io_submit(cb.ctx->ctx, 1, iocbs);
> +
> +    return ret != -EINVAL;
> +}
> ===
> 
> To confirm:
> * Do we need a revised patch V3? I'm testing one with the above
> function to check if IO_CMD_FDSYNC is supported. If it returns true we
> call laio_co_submit(..., QEMU_AIO_FLUSH, ), else fallback to
> thread-pool.

If you are already developing and testing it then I think a v3 with
laio_has_fdsync() would be great.

Thanks,
Stefan

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