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

[Jeff Cody <jcody@redhat.com>]

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.

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