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Date: Thu, 11 Sep 2014 15:18:48 +0200
From: =?iso-8859-1?Q?Beno=EEt?= Canet <benoit.canet@irqsave.net>
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Subject: Re: [Qemu-devel] [PATCH 08/23] block: Eliminate BlockDriverState
 member device_name[]
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To: Eric Blake <eblake@redhat.com>
Cc: =?iso-8859-1?Q?Beno=EEt?= Canet <benoit.canet@irqsave.net>, kwolf@redhat.com, famz@redhat.com, Markus Armbruster <armbru@redhat.com>, qemu-devel@nongnu.org, stefanha@redhat.com

The Thursday 11 Sep 2014 =E0 07:00:41 (-0600), Eric Blake wrote :
> On 09/11/2014 05:34 AM, Beno=EEt Canet wrote:
> > The Wednesday 10 Sep 2014 =E0 10:13:37 (+0200), Markus Armbruster wro=
te :
> >> 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, the=
n
> >> it's owned by a BlockBackend.
>=20
> [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]
>=20
> >> =20
> >> -const char *bdrv_get_device_name(BlockDriverState *bs)
> >> +const char *bdrv_get_device_name(const BlockDriverState *bs)
> >>  {
> >> -    return bs->device_name;
> >> +    const char *name =3D bs->blk ? blk_name(bs->blk) : NULL;
> >> +    return name ?: "";
> >>  }
> >=20
> > Why not ?
> >=20
> >     return bs->blk ? blk_name(bs->blk) : "";
>=20
> 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 =3D g_new0(BlockBackend, 1);
> +    =20
> +    assert(name && name[0]);

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