Re: [Qemu-devel] [PATCH 08/23] block: Eliminate BlockDriverState member device_name[]

[Benoît Canet]

The Thursday 11 Sep 2014 à 07:00:41 (-0600), Eric Blake wrote :
> On 09/11/2014 05:34 AM, Benoît Canet wrote:
> > The Wednesday 10 Sep 2014 à 10:13:37 (+0200), Markus Armbruster wrote :
> >> device_name[] is can become non-empty only in bdrv_new_named() and
> >> bdrv_move_feature_fields().  The latter is used only to undo damage
> >> done by bdrv_swap().  The former is called only by blk_new_with_bs().
> >> Therefore, when a BlockDriverState's device_name[] is non-empty, then
> >> it's owned by a BlockBackend.
> 
> [lots of lines trimmed - it's not only okay, but desirable to trim out
> portions of a patch that you are okay with, in order to call attention
> to the problem spots that you are commenting on without making the
> reader have to scroll through pages of quoted context]
> 
> >>  
> >> -const char *bdrv_get_device_name(BlockDriverState *bs)
> >> +const char *bdrv_get_device_name(const BlockDriverState *bs)
> >>  {
> >> -    return bs->device_name;
> >> +    const char *name = bs->blk ? blk_name(bs->blk) : NULL;
> >> +    return name ?: "";
> >>  }
> > 
> > Why not ?
> > 
> >     return bs->blk ? blk_name(bs->blk) : "";
> 
> If I understand right, it was because blk_name(bs->blk) may return NULL,

It think it can't: see patch 2 extract:

> +BlockBackend *blk_new(const char *name, Error **errp)
> +{
> +    BlockBackend *blk = g_new0(BlockBackend, 1);
> +     
> +    assert(name && name[0]);

> but this function is guaranteed to return non-NULL.