block: check bdrv_in_use() before blockdev operations

Long-running block operations like block migration and image streaming
must have continual access to their block device.  It is not safe to
perform operations like hotplug, eject, change, resize, commit, or
external snapshot while a long-running operation is in progress.

This patch adds the missing bdrv_in_use() checks so that block migration
and image streaming never have the rug pulled out from underneath them.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -1020,6 +1020,10 @@ int bdrv_commit(BlockDriverState *bs)
         return -EACCES;
     }
 
+    if (bdrv_in_use(bs) || bdrv_in_use(bs->backing_hd)) {
+        return -EBUSY;
+    }
+
     backing_drv = bs->backing_hd->drv;
     ro = bs->backing_hd->read_only;
     strncpy(filename, bs->backing_hd->filename, sizeof(filename));

blockdev.c

@@ -592,12 +592,18 @@ void do_commit(Monitor *mon, const QDict *qdict)
     if (!strcmp(device, "all")) {
         bdrv_commit_all();
     } else {
+        int ret;
+
         bs = bdrv_find(device);
         if (!bs) {
             qerror_report(QERR_DEVICE_NOT_FOUND, device);
             return;
         }
-        bdrv_commit(bs);
+        ret = bdrv_commit(bs);
+        if (ret == -EBUSY) {
+            qerror_report(QERR_DEVICE_IN_USE, device);
+            return;
+        }
     }
 }
 
@@ -616,6 +622,10 @@ void qmp_blockdev_snapshot_sync(const char *device, const char *snapshot_file,
         error_set(errp, QERR_DEVICE_NOT_FOUND, device);
         return;
     }
+    if (bdrv_in_use(bs)) {
+        error_set(errp, QERR_DEVICE_IN_USE, device);
+        return;
+    }
 
     pstrcpy(old_filename, sizeof(old_filename), bs->filename);
 
@@ -667,6 +677,10 @@ void qmp_blockdev_snapshot_sync(const char *device, const char *snapshot_file,
 
 static void eject_device(BlockDriverState *bs, int force, Error **errp)
 {
+    if (bdrv_in_use(bs)) {
+        error_set(errp, QERR_DEVICE_IN_USE, bdrv_get_device_name(bs));
+        return;
+    }
     if (!bdrv_dev_has_removable_media(bs)) {
         error_set(errp, QERR_DEVICE_NOT_REMOVABLE, bdrv_get_device_name(bs));
         return;