[Qemu-devel] [PATCH 08/11] migration: implement bdrv_all_find_vmstate_bs and bdrv_unlock helpers

["Denis V. Lunev" <den@openvz.org>]

bdrv_all_find_vmstate_bs will return locked BlockDriverState. The code
written in the way to avoid nested locking taking into account that
patch for locking inside qemu_fopen_bdrv/qemu_fclose is acceptable.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Juan Quintela <quintela@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
---
 block/snapshot.c         | 21 +++++++++++++++++++++
 include/block/snapshot.h |  3 +++
 migration/savevm.c       | 23 ++++++++---------------
 3 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/block/snapshot.c b/block/snapshot.c
index bb3bfd5..e196c9b 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -446,3 +446,24 @@ int bdrv_all_find_snapshot(const char *name, BlockDriverState **first_bad_bs)
     *first_bad_bs = bs;
     return err;
 }
+
+BlockDriverState *bdrv_all_find_vmstate_bs(void)
+{
+    BlockDriverState *bs = NULL;
+
+    while ((bs = bdrv_next(bs))) {
+        AioContext *ctx = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(ctx);
+        if (bdrv_can_snapshot(bs)) {
+            return bs;
+        }
+        aio_context_release(ctx);
+    }
+    return NULL;
+}
+
+void bdrv_unlock(BlockDriverState *bs)
+{
+    aio_context_release(bdrv_get_aio_context(bs));
+}
diff --git a/include/block/snapshot.h b/include/block/snapshot.h
index 44c3a38..1f45f51 100644
--- a/include/block/snapshot.h
+++ b/include/block/snapshot.h
@@ -88,4 +88,7 @@ int bdrv_all_delete_snapshot(const char *name, BlockDriverState **first_bsd_bs,
 int bdrv_all_goto_snapshot(const char *name, BlockDriverState **first_bsd_bs);
 int bdrv_all_find_snapshot(const char *name, BlockDriverState **first_bad_bs);
 
+BlockDriverState *bdrv_all_find_vmstate_bs(void);
+void bdrv_unlock(BlockDriverState *bs);
+
 #endif
diff --git a/migration/savevm.c b/migration/savevm.c
index dbcb313..9339f2e 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1237,17 +1237,6 @@ out:
     return ret;
 }
 
-static BlockDriverState *find_vmstate_bs(void)
-{
-    BlockDriverState *bs = NULL;
-    while ((bs = bdrv_next(bs))) {
-        if (bdrv_can_snapshot(bs)) {
-            return bs;
-        }
-    }
-    return NULL;
-}
-
 void hmp_savevm(Monitor *mon, const QDict *qdict)
 {
     BlockDriverState *bs, *bs1;
@@ -1293,8 +1282,8 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
     sn->date_nsec = tv.tv_usec * 1000;
     sn->vm_clock_nsec = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 
-    bs = find_vmstate_bs();
-    if (!bs) {
+    bs = bdrv_all_find_vmstate_bs();
+    if (bs == NULL) {
         monitor_printf(mon, "No block device can accept snapshots\n");
         goto the_end;
     }
@@ -1312,6 +1301,7 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
         localtime_r((const time_t *)&tv.tv_sec, &tm);
         strftime(sn->name, sizeof(sn->name), "vm-%Y%m%d%H%M%S", &tm);
     }
+    bdrv_unlock(bs);
 
     /* save the VM state */
     f = qemu_fopen_bdrv(bs, 1);
@@ -1395,7 +1385,7 @@ int load_vmstate(const char *name)
         return ret;
     }
 
-    bs_vm_state = find_vmstate_bs();
+    bs_vm_state = bdrv_all_find_vmstate_bs();
     if (!bs_vm_state) {
         error_report("No block device supports snapshots");
         return -ENOTSUP;
@@ -1403,6 +1393,8 @@ int load_vmstate(const char *name)
 
     /* Don't even try to load empty VM states */
     ret = bdrv_snapshot_find(bs_vm_state, &sn, name);
+    bdrv_unlock(bs_vm_state);
+
     if (ret < 0) {
         return ret;
     } else if (sn.vm_state_size == 0) {
@@ -1464,13 +1456,14 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
     int total;
     int *available_snapshots;
 
-    bs = find_vmstate_bs();
+    bs = bdrv_all_find_vmstate_bs();
     if (!bs) {
         monitor_printf(mon, "No available block device supports snapshots\n");
         return;
     }
 
     nb_sns = bdrv_snapshot_list(bs, &sn_tab);
+    bdrv_unlock(bs);
     if (nb_sns < 0) {
         monitor_printf(mon, "bdrv_snapshot_list: error %d\n", nb_sns);
         return;
-- 
2.5.0