On 05/23/2016 06:54 AM, Paolo Bonzini wrote: > scsi-block will be able to do FUA just by passing the request through > to the LUN (which is also more efficient); there is no need to emulate > it like we do for scsi-disk. > > Add a new method to distinguish this. > > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> > --- > hw/scsi/scsi-disk.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) >
> @@ -239,7 +241,7 @@ static void scsi_write_do_fua(SCSIDiskReq *r)
> goto done;
> }
>
> - if (scsi_is_cmd_fua(&r->req.cmd)) {
> + if (r->need_fua_emulation) {
BDRV_REQ_FUA is defined for writes,...
> block_acct_start(blk_get_stats(s->qdev.conf.blk), &r->acct, 0,
> BLOCK_ACCT_FLUSH);
> r->req.aiocb = blk_aio_flush(s->qdev.conf.blk, scsi_aio_complete, r);
> @@ -416,7 +418,7 @@ static void scsi_read_data(SCSIRequest *req)
>
> first = !r->started;
> r->started = true;
> - if (first && scsi_is_cmd_fua(&r->req.cmd)) {
> + if (first && r->need_fua_emulation) {
...but while FUA semantics are definitely defined in SCSI for reads, I
don't know if we've properly wired them up in our block layer for that
purpose. In particular, while bdrv_driver_pwritev() definitely has a
flush fallback if .supported_write_flags lacks BDRV_REQ_FUA,
bdrv_driver_preadv() does not currently look at flags.
The idea makes sense, but I don't know if it is incomplete without first
making sure FUA works on reads throughout the block layer.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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