Re: [Qemu-devel] [PATCH 5/5] block: Always enable discard on the protocol level

[Kevin Wolf <kwolf@redhat.com>]

Am 14.06.2013 um 00:06 hat Paolo Bonzini geschrieben:
> Il 13/06/2013 07:47, Kevin Wolf ha scritto:
> > Turning on discard options in qcow2 doesn't help a lot when the discard
> > requests that it issues are thrown away by the raw-posix layer. This
> > patch always enables discard functionality on the protocol level so that
> > it's the image format's responsibility to send (or not) discard
> > requests. Requests sent by the guest will be allowed or ignored by the
> > top level BlockDriverState, which depends on the discard=... option like
> > before.
> > 
> > In particular, this means that even without specifying options, the
> > qcow2 default of discarding deleted snapshots actually takes effect now,
> > both for qemu and qemu-img.
> > 
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  block.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/block.c b/block.c
> > index 79ad33d..0a7cf2f 100644
> > --- a/block.c
> > +++ b/block.c
> > @@ -1045,7 +1045,7 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
> >      extract_subqdict(options, &file_options, "file.");
> >  
> >      ret = bdrv_file_open(&file, filename, file_options,
> > -                         bdrv_open_flags(bs, flags));
> > +                         bdrv_open_flags(bs, flags | BDRV_O_UNMAP));
> >      if (ret < 0) {
> >          goto fail;
> >      }
> > 
> 
> Can you still disable it with -drive file.discard=ignore?

This requires a few more changes (basically moving BDRV_O_UNMAP from
flags into a boolean in the QDict), but I think eventually we'll want to
allow this.

Kevin