Re: [Qemu-devel] [PATCH 02/18] block: add error parameter to bdrv_snapshot_create() and related functions

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 31 Aug 2012 14:18:55 +0200
Kevin Wolf <kwolf@redhat.com> wrote:

> Am 31.08.2012 08:26, schrieb Markus Armbruster:
> > Luiz Capitulino <lcapitulino@redhat.com> writes:
> > 
> >> On Wed, 15 Aug 2012 09:41:43 +0200
> >> Pavel Hrdina <phrdina@redhat.com> wrote:
> >>
> >>> Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
> >>> ---
> >>>  block.c                | 25 +++++++++++++++++--------
> >>>  block.h                |  3 ++-
> >>>  block/qcow2-snapshot.c |  9 ++++++++-
> >>>  block/qcow2.h          |  4 +++-
> >>>  block/rbd.c            | 20 ++++++++++++++------
> >>>  block/sheepdog.c       | 17 +++++++++--------
> >>>  block_int.h            |  3 ++-
> >>>  qemu-img.c             |  2 +-
> >>>  savevm.c               |  2 +-
> >>>  9 files changed, 57 insertions(+), 28 deletions(-)
> >>>
> >>> diff --git a/block.c b/block.c
> >>> index 016858b..8bc49b7 100644
> >>> --- a/block.c
> >>> +++ b/block.c
> >>> @@ -2661,16 +2661,25 @@ BlockDriverState *bdrv_snapshots(void)
> >>>  }
> >>>  
> >>>  int bdrv_snapshot_create(BlockDriverState *bs,
> >>> -                         QEMUSnapshotInfo *sn_info)
> >>> +                         QEMUSnapshotInfo *sn_info,
> >>> +                         Error **errp)
> >>>  {
> >>>      BlockDriver *drv = bs->drv;
> >>> -    if (!drv)
> >>> -        return -ENOMEDIUM;
> >>> -    if (drv->bdrv_snapshot_create)
> >>> -        return drv->bdrv_snapshot_create(bs, sn_info);
> >>> -    if (bs->file)
> >>> -        return bdrv_snapshot_create(bs->file, sn_info);
> >>> -    return -ENOTSUP;
> >>> +    int ret;
> >>> +
> >>> +    if (!drv) {
> >>> +        error_set(errp, QERR_DEVICE_HAS_NO_MEDIUM, bdrv_get_device_name(bs));
> >>
> >> We should only use QERR_ macros for the errors listed in the ErrorClass enum
> >> (except GenericError), all other errors should generally use error_setg(), like
> >> this:
> >>
> >>  error_setg(errp, "device '%s' has no medium);
> >>
> >>> +        ret = -ENOMEDIUM;
> >>
> >> And, usually, we should get rid of errno propagation. There are two cases here:
> > 
> > The block layer consistently[*] uses -errno return values.  Its
> > consistency is valuable, and I'm a bit reluctant to break it.  Maybe a
> > new rule "returns -errno, except when it has an Error ** argument" could
> > work.  I'd like to hear Kevin's advice on this.
> 
> I'd rather not remove existing -errno returns if there's not good reason
> why we can't provide them (or can't do so easily at least).

Yes, I agree. Let me evaluate this calmly. I'll try to come with a better
proposal soon.