Re: [Qemu-block] [PATCH v7 1/9] mirror: inherit supported write/zero flags

[Anton Nefedov]

On 29/1/2018 10:26 PM, Eric Blake wrote:
> On 01/29/2018 01:21 PM, Max Reitz wrote:
> > On 2018-01-18 18:48, Anton Nefedov wrote:
> > > Signed-off-by: Anton Nefedov <address@hidden>
> > > Reviewed-by: Eric Blake <address@hidden>
> > > Reviewed-by: Alberto Garcia <address@hidden>
> > > ---
> > >   block/mirror.c | 5 +++++
> > >   1 file changed, 5 insertions(+)
> > >
> > > diff --git a/block/mirror.c b/block/mirror.c
> > > index c9badc1..d18ec65 100644
> > > --- a/block/mirror.c
> > > +++ b/block/mirror.c
> > > @@ -1064,6 +1064,11 @@ static void 
> > > bdrv_mirror_top_refresh_filename(BlockDriverState *bs, QDict *opts)
> > >       bdrv_refresh_filename(bs->backing->bs);
> > >       pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
> > >               bs->backing->bs->filename);
> > > +    bs->supported_write_flags = BDRV_REQ_FUA &
> > > +        bs->backing->bs->supported_write_flags;
> > > +    bs->supported_zero_flags =
> > > +        (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
> > > +        bs->backing->bs->supported_zero_flags;
> > >   }
> > >   
> > >   static void bdrv_mirror_top_close(BlockDriverState *bs)
> >
> > Fundamentally OK, but why is this in *_refresh_filename()?
>
> Indeed, I missed that (or maybe it got moved during a botched rebase?).
> For comparison, blkdebug sets it during blkdebug_open(), and nbd sets it
> during nbd_client_init() (called during nbd_open()).

We need a backing bs here and I believe it's not generally set at the 
time of .bdrv_open()