[Qemu-devel] [PATCH v6 7/8] nbd: use BlockDriverState refcnt

[Fam Zheng <famz@redhat.com>]

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;
+    }
 }
 
 void nbd_export_get(NBDExport *exp)
-- 
1.8.3.1