Re: [Qemu-devel] [PATCH 8/8] nbd: use BlockDriverState refcnt

[Jeff Cody <jcody@redhat.com>]

On Thu, Jul 25, 2013 at 09:01:41AM -0400, Jeff Cody wrote:
> On Thu, Jul 25, 2013 at 05:01:46PM +0800, Fam Zheng wrote:
> > Previously, nbd calls drive_get_ref() on the drive of bs. A BDS doesn't
> > always have associated dinfo, which nbd doesn't care either. We already
> > have BDS ref count, so use it to make it safe for a BDS w/o blockdev.
> > 
> > Signed-off-by: Fam Zheng <famz@redhat.com>
> > ---
> >  blockdev-nbd.c | 10 +---------
> >  nbd.c          |  5 +++++
> >  2 files changed, 6 insertions(+), 9 deletions(-)
> > 
> > diff --git a/blockdev-nbd.c b/blockdev-nbd.c
> > index 95f10c8..922cf56 100644
> > --- a/blockdev-nbd.c
> > +++ b/blockdev-nbd.c
> > @@ -69,12 +69,6 @@ static void nbd_close_notifier(Notifier *n, void *data)
> >      g_free(cn);
> >  }
> >  
> > -static void nbd_server_put_ref(NBDExport *exp)
> > -{
> > -    BlockDriverState *bs = nbd_export_get_blockdev(exp);
> > -    drive_put_ref(drive_get_by_blockdev(bs));
> > -}
> > -
> >  void qmp_nbd_server_add(const char *device, bool has_writable, bool writable,
> >                          Error **errp)
> >  {
> > @@ -105,11 +99,9 @@ void qmp_nbd_server_add(const char *device, bool has_writable, bool writable,
> >          writable = false;
> >      }
> >  
> > -    exp = nbd_export_new(bs, 0, -1, writable ? 0 : NBD_FLAG_READ_ONLY,
> > -                         nbd_server_put_ref);
> > +    exp = nbd_export_new(bs, 0, -1, writable ? 0 : NBD_FLAG_READ_ONLY, NULL);
> >  
> >      nbd_export_set_name(exp, device);
> > -    drive_get_ref(drive_get_by_blockdev(bs));
> >  
> >      n = g_malloc0(sizeof(NBDCloseNotifier));
> >      n->n.notify = nbd_close_notifier;
> > diff --git a/nbd.c b/nbd.c
> > index 2606403..f258cdd 100644
> > --- a/nbd.c
> > +++ b/nbd.c
> > @@ -881,6 +881,7 @@ NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset,
> >      exp->nbdflags = nbdflags;
> >      exp->size = size == -1 ? bdrv_getlength(bs) : size;
> >      exp->close = close;
> > +    bdrv_ref(bs);
> >      return exp;
> >  }
> >  
> > @@ -927,6 +928,10 @@ void nbd_export_close(NBDExport *exp)
> >      }
> >      nbd_export_set_name(exp, NULL);
> >      nbd_export_put(exp);
> > +    if (exp->bs) {
> > +        bdrv_unref(exp->bs);
> > +        exp->bs = NULL;
> > +    }
> 
> Same thing here - if the refcnt is ever > 1, then this leaks exp->bs.
>

Nevermind - since bs continues to exist elsewhere (and would
presumably be unrefed there), then this would not leak exp->bs.

> >  }
> >  
> >  void nbd_export_get(NBDExport *exp)
> > -- 
> > 1.8.3.2
> > 
> >