Re: [Qemu-devel] [PATCH for-2.10 2/9] block: do not set BDS read_only if copy_on_read enabled

[Jeff Cody <jcody@redhat.com>]

On Wed, Apr 05, 2017 at 03:16:38PM -0400, John Snow wrote:
> 
> 
> On 04/05/2017 02:28 PM, Jeff Cody wrote:
> > A few block drivers will set the BDS read_only flag from their
> > .bdrv_open() function.  This means the bs->read_only flag could
> > be set after we enable copy_on_read, as the BDRV_O_COPY_ON_READ
> > flag check occurs prior to the call to bdrv->bdrv_open().
> > 
> > This adds an error return to bdrv_set_read_only(), and an error will be
> > return if we try to set the BDS to read_only while copy_on_read is
> > enabled.
> > 
> > Signed-off-by: Jeff Cody <jcody@redhat.com>
> > ---
> >  block.c               | 10 +++++++++-
> >  block/bochs.c         |  5 ++++-
> >  block/cloop.c         |  5 ++++-
> >  block/dmg.c           |  6 +++++-
> >  block/rbd.c           |  6 +++++-
> >  block/vvfat.c         | 15 ++++++++++++---
> >  include/block/block.h |  2 +-
> >  7 files changed, 40 insertions(+), 9 deletions(-)
> > 
> > diff --git a/block.c b/block.c
> > index 7b4c7ef..f60d5ea 100644
> > --- a/block.c
> > +++ b/block.c
> > @@ -192,9 +192,17 @@ void path_combine(char *dest, int dest_size,
> >      }
> >  }
> >  
> > -void bdrv_set_read_only(BlockDriverState *bs, bool read_only)
> > +int bdrv_set_read_only(BlockDriverState *bs, bool read_only, Error **errp)
> >  {
> > +    /* Do not set read_only if copy_on_read is enabled */
> > +    if (bs->copy_on_read && read_only) {
> > +        error_setg(errp, "Cannot set node '%s' to r/o while COW enabled",
> 
> COW?
>

Mooo! You are right, that should be COR (or better yet, I should just write
it out - copy on read).

> > +                   bdrv_get_device_or_node_name(bs));
> > +        return -EINVAL;
> > +    }
> > +
> >      bs->read_only = read_only;
> > +    return 0;
> >  }
> >  
> >  void bdrv_get_full_backing_filename_from_filename(const char *backed,
> > diff --git a/block/bochs.c b/block/bochs.c
> > index bdc2831..a759b6e 100644
> > --- a/block/bochs.c
> > +++ b/block/bochs.c
> > @@ -110,7 +110,10 @@ static int bochs_open(BlockDriverState *bs, QDict *options, int flags,
> >          return -EINVAL;
> >      }
> >  
> > -    bdrv_set_read_only(bs, true); /* no write support yet */
> > +    ret = bdrv_set_read_only(bs, true, errp); /* no write support yet */
> > +    if (ret < 0) {
> > +        return ret;
> > +    }
> >  
> >      ret = bdrv_pread(bs->file, 0, &bochs, sizeof(bochs));
> >      if (ret < 0) {
> > diff --git a/block/cloop.c b/block/cloop.c
> > index 11f17c8..d6597fc 100644
> > --- a/block/cloop.c
> > +++ b/block/cloop.c
> > @@ -72,7 +72,10 @@ static int cloop_open(BlockDriverState *bs, QDict *options, int flags,
> >          return -EINVAL;
> >      }
> >  
> > -    bdrv_set_read_only(bs, true);
> > +    ret = bdrv_set_read_only(bs, true, errp);
> > +    if (ret < 0) {
> > +        return ret;
> > +    }
> >  
> >      /* read header */
> >      ret = bdrv_pread(bs->file, 128, &s->block_size, 4);
> > diff --git a/block/dmg.c b/block/dmg.c
> > index 27ce4a6..900ae5a 100644
> > --- a/block/dmg.c
> > +++ b/block/dmg.c
> > @@ -419,8 +419,12 @@ static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
> >          return -EINVAL;
> >      }
> >  
> > +    ret = bdrv_set_read_only(bs, true, errp);
> > +    if (ret < 0) {
> > +        return ret;
> > +    }
> > +
> >      block_module_load_one("dmg-bz2");
> > -    bdrv_set_read_only(bs, true);
> >  
> >      s->n_chunks = 0;
> >      s->offsets = s->lengths = s->sectors = s->sectorcounts = NULL;
> > diff --git a/block/rbd.c b/block/rbd.c
> > index 6ad2904..328e4a9 100644
> > --- a/block/rbd.c
> > +++ b/block/rbd.c
> > @@ -641,7 +641,11 @@ static int qemu_rbd_open(BlockDriverState *bs, QDict *options, int flags,
> >          goto failed_open;
> >      }
> >  
> > -    bdrv_set_read_only(bs, (s->snap != NULL));
> > +    r = bdrv_set_read_only(bs, (s->snap != NULL), &local_err);
> > +    if (r < 0) {
> > +        error_propagate(errp, local_err);
> > +        goto failed_open;
> > +    }
> >  
> >      qemu_opts_del(opts);
> >      return 0;
> > diff --git a/block/vvfat.c b/block/vvfat.c
> > index d4ce6d7..34a2854 100644
> > --- a/block/vvfat.c
> > +++ b/block/vvfat.c
> > @@ -1156,8 +1156,6 @@ static int vvfat_open(BlockDriverState *bs, QDict *options, int flags,
> >  
> >      s->current_cluster=0xffffffff;
> >  
> > -    /* read only is the default for safety */
> > -    bdrv_set_read_only(bs, true);
> >      s->qcow = NULL;
> >      s->qcow_filename = NULL;
> >      s->fat2 = NULL;
> > @@ -1173,7 +1171,18 @@ static int vvfat_open(BlockDriverState *bs, QDict *options, int flags,
> >          if (ret < 0) {
> >              goto fail;
> >          }
> > -        bdrv_set_read_only(bs, false);
> > +        ret = bdrv_set_read_only(bs, false, &local_err);
> > +        if (ret < 0) {
> > +            error_propagate(errp, local_err);
> > +            goto fail;
> > +        }
> > +    } else  {
> > +        /* read only is the default for safety */
> > +        ret = bdrv_set_read_only(bs, true, &local_err);
> > +        if (ret < 0) {
> > +            error_propagate(errp, local_err);
> > +            goto fail;
> > +        }
> >      }
> >  
> >      bs->total_sectors = cyls * heads * secs;
> > diff --git a/include/block/block.h b/include/block/block.h
> > index 06c9032..beb563a 100644
> > --- a/include/block/block.h
> > +++ b/include/block/block.h
> > @@ -426,7 +426,7 @@ int bdrv_is_allocated_above(BlockDriverState *top, BlockDriverState *base,
> >                              int64_t sector_num, int nb_sectors, int *pnum);
> >  
> >  bool bdrv_is_read_only(BlockDriverState *bs);
> > -void bdrv_set_read_only(BlockDriverState *bs, bool read_only);
> > +int bdrv_set_read_only(BlockDriverState *bs, bool read_only, Error **errp);
> >  bool bdrv_is_sg(BlockDriverState *bs);
> >  bool bdrv_is_inserted(BlockDriverState *bs);
> >  int bdrv_media_changed(BlockDriverState *bs);
> >