On Mon, Apr 07, 2025 at 08:47:30AM -0700, Pinku Deb Nath wrote:
> Full Unit Access (FUA) is an optimization where a disk write with the
> flag set will be persisted to disk immediately instead of potentially
> remaining in the disk's write cache.
>
> This commit address the todo task
> for using pwritev2() with RWF_DSYNC in the thread pool section of
> raw_co_prw(), if pwritev2() with RWF_DSYNC is available in the host,
> which is always the case for Linux kernel >= 4.7.
[Side note - I should take a look at using this syscall in libnbd's
file plugin]
> @@ -1698,10 +1718,16 @@ static ssize_t handle_aiocb_rw_vector(RawPosixAIOData
> *aiocb)
>
> len = RETRY_ON_EINTR(
> (aiocb->aio_type & (QEMU_AIO_WRITE | QEMU_AIO_ZONE_APPEND)) ?
> - qemu_pwritev(aiocb->aio_fildes,
> - aiocb->io.iov,
> - aiocb->io.niov,
> - aiocb->aio_offset) :
> + (aiocb->flags & BDRV_REQ_FUA) ?
> + qemu_pwritev_fua(aiocb->aio_fildes,
> + aiocb->io.iov,
> + aiocb->io.niov,
> + aiocb->aio_offset,
> + aiocb) :
> + qemu_pwritev(aiocb->aio_fildes,
> + aiocb->io.iov,
> + aiocb->io.niov,
> + aiocb->aio_offset) :
> qemu_preadv(aiocb->aio_fildes,
> aiocb->io.iov,
> aiocb->io.niov,
This ?: chain is getting ridiculous. Can we instead do:
if (aiocb->aio_type & (QEMU_AIO_WRITE | QEMU_AIO_ZONE_APPEND)) {
if (aiocb->flags & BDRV_REQ_FUA) {
fn = qemu_pwritev_fua;
} else {
fn = qemu_pwritev;
}
} else {
fn = qemu_preadv;
}
len = RETRY_ON_EINTR(fn(aiocb->aio_fildes, ... ))
by having all of the various dispatch functions take the same
signature and a suitably-defined fn function pointer variable?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
