[Qemu-devel] [PATCH for-2.7 04/15] block: Introduce image file locking interface

[Fam Zheng <famz@redhat.com>]

Block drivers can implement this new operation .bdrv_lockf to actually lock the
image in the protocol specific way.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block.c                   | 25 +++++++++++++++++++++++++
 include/block/block.h     |  8 ++++++++
 include/block/block_int.h |  5 +++++
 3 files changed, 38 insertions(+)

diff --git a/block.c b/block.c
index d4939b4..7f6e903 100644
--- a/block.c
+++ b/block.c
@@ -995,6 +995,15 @@ static int bdrv_open_common(BlockDriverState *bs, BdrvChild *file,
         goto free_and_fail;
     }
 
+    if (!(open_flags & BDRV_O_NO_LOCK)) {
+        BdrvLockfCmd cmd = open_flags & BDRV_O_RDWR ? BDRV_LOCKF_RWLOCK :
+                                                      BDRV_LOCKF_ROLOCK;
+        ret = bdrv_lockf(bs, cmd, errp);
+        if (ret != 0 && ret != -ENOTSUP) {
+            goto free_and_fail;
+        }
+    }
+
     ret = refresh_total_sectors(bs, bs->total_sectors);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not refresh total sector count");
@@ -2141,6 +2150,10 @@ static void bdrv_close(BlockDriverState *bs)
         blk_dev_change_media_cb(bs->blk, false);
     }
 
+    if (bs->drv && !(bs->open_flags & BDRV_O_NO_LOCK)) {
+        bdrv_lockf(bs, BDRV_LOCKF_UNLOCK, &error_abort);
+    }
+
     if (bs->drv) {
         BdrvChild *child, *next;
 
@@ -3981,3 +3994,15 @@ void bdrv_refresh_filename(BlockDriverState *bs)
         QDECREF(json);
     }
 }
+
+int bdrv_lockf(BlockDriverState *bs, BdrvLockfCmd cmd, Error **errp)
+{
+    if (!bs->drv) {
+        error_setg(errp, "No medium to lock");
+        return -ENOMEDIUM;
+    } else if (!bs->drv->bdrv_lockf) {
+        return -ENOTSUP;
+    } else {
+        return bs->drv->bdrv_lockf(bs, cmd, errp);
+    }
+}
diff --git a/include/block/block.h b/include/block/block.h
index b803597..36e1271 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -542,4 +542,12 @@ void bdrv_drained_begin(BlockDriverState *bs);
  */
 void bdrv_drained_end(BlockDriverState *bs);
 
+typedef enum {
+    BDRV_LOCKF_RWLOCK,
+    BDRV_LOCKF_ROLOCK,
+    BDRV_LOCKF_UNLOCK,
+} BdrvLockfCmd;
+
+int bdrv_lockf(BlockDriverState *bs, BdrvLockfCmd cmd, Error **errp);
+
 #endif
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 10d8759..0a79eba 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -317,6 +317,11 @@ struct BlockDriver {
      */
     void (*bdrv_drain)(BlockDriverState *bs);
 
+    /**
+     * Lock/unlock the image.
+     */
+    int (*bdrv_lockf)(BlockDriverState *bs, BdrvLockfCmd cmd, Error **errp);
+
     QLIST_ENTRY(BlockDriver) list;
 };
 
-- 
2.8.0