Re: [PATCH 5/6] block/nbd: Do not force-cap *pnum

[Vladimir Sementsov-Ogievskiy]

18.06.2021 23:20, Eric Blake wrote:
> On Thu, Jun 17, 2021 at 05:52:46PM +0200, Max Reitz wrote:
> > bdrv_co_block_status() does it for us, we do not need to do it here.
> >
> > The advantage of not capping *pnum is that bdrv_co_block_status() can
> > cache larger data regions than requested by its caller.
> >
> > Signed-off-by: Max Reitz <mreitz@redhat.com>
> > ---
> >   block/nbd.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
>
> Reviewed-by: Eric Blake <eblake@redhat.com>
>
> > diff --git a/block/nbd.c b/block/nbd.c
> > index 616f9ae6c4..930bd234de 100644
> > --- a/block/nbd.c
> > +++ b/block/nbd.c
> > @@ -1702,7 +1702,7 @@ static int coroutine_fn nbd_client_co_block_status(
> >           .type = NBD_CMD_BLOCK_STATUS,
> >           .from = offset,
> >           .len = MIN(QEMU_ALIGN_DOWN(INT_MAX, bs->bl.request_alignment),
> > -                   MIN(bytes, s->info.size - offset)),
> > +                   s->info.size - offset),
> >           .flags = NBD_CMD_FLAG_REQ_ONE,
>
> I'd love to someday get rid of using NBD_CMD_FLAG_REQ_ONE (so the
> server can reply with more extents in one go), but that's a bigger
> task and unrelated to your block-layer cache.

I think for this to work, the generic block_status should be updated so we can 
work with several extents in one go.


--
Best regards,
Vladimir