[Qemu-devel] [PATCH for-2.7 v2 04/17] block: Introduce image file locking

[Fam Zheng]

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

Signed-off-by: Fam Zheng <f...@redhat.com>
---
 block.c                   | 42 ++++++++++++++++++++++++++++++++++++++++++
 include/block/block_int.h | 12 ++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/block.c b/block.c
index 1c575e4..7971a25 100644
--- a/block.c
+++ b/block.c
@@ -846,6 +846,34 @@ out:
     g_free(gen_node_name);
 }
 
+static int bdrv_lock_unlock_image_do(BlockDriverState *bs, bool lock_image)
+{
+    int cmd = BDRV_LOCKF_UNLOCK;
+
+    if (bs->image_locked == lock_image) {
+        return 0;
+    } else if (!bs->drv) {
+        return -ENOMEDIUM;
+    } else if (!bs->drv->bdrv_lockf) {
+        return 0;
+    }
+    if (lock_image) {
+        cmd = bs->open_flags & BDRV_O_RDWR ? BDRV_LOCKF_RWLOCK :
+                                             BDRV_LOCKF_ROLOCK;
+    }
+    return bs->drv->bdrv_lockf(bs, cmd);
+}
+
+static int bdrv_lock_image(BlockDriverState *bs)
+{
+    return bdrv_lock_unlock_image_do(bs, true);
+}
+
+static int bdrv_unlock_image(BlockDriverState *bs)
+{
+    return bdrv_lock_unlock_image_do(bs, false);
+}
+
 static QemuOptsList bdrv_runtime_opts = {
     .name = "bdrv_common",
     .head = QTAILQ_HEAD_INITIALIZER(bdrv_runtime_opts.head),
@@ -995,6 +1023,14 @@ static int bdrv_open_common(BlockDriverState *bs, 
BdrvChild *file,
         goto free_and_fail;
     }
 
+    if (!(open_flags & (BDRV_O_NO_LOCK | BDRV_O_INACTIVE))) {
+        ret = bdrv_lock_image(bs);
+        if (ret) {
+            error_setg(errp, "Failed to lock image");
+            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");
@@ -2144,6 +2180,7 @@ static void bdrv_close(BlockDriverState *bs)
     if (bs->drv) {
         BdrvChild *child, *next;
 
+        bdrv_unlock_image(bs);
         bs->drv->bdrv_close(bs);
         bs->drv = NULL;
 
@@ -3230,6 +3267,9 @@ void bdrv_invalidate_cache(BlockDriverState *bs, Error 
**errp)
         error_setg_errno(errp, -ret, "Could not refresh total sector count");
         return;
     }
+    if (!(bs->open_flags & BDRV_O_NO_LOCK)) {
+        bdrv_lock_image(bs);
+    }
 }
 
 void bdrv_invalidate_cache_all(Error **errp)
@@ -3262,6 +3302,7 @@ static int bdrv_inactivate(BlockDriverState *bs)
     }
 
     bs->open_flags |= BDRV_O_INACTIVE;
+    ret = bdrv_unlock_image(bs);
     return 0;
 }
 
@@ -3981,3 +4022,4 @@ void bdrv_refresh_filename(BlockDriverState *bs)
         QDECREF(json);
     }
 }
+
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 10d8759..ffa30b0 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -85,6 +85,12 @@ typedef struct BdrvTrackedRequest {
     struct BdrvTrackedRequest *waiting_for;
 } BdrvTrackedRequest;
 
+typedef enum {
+    BDRV_LOCKF_RWLOCK,
+    BDRV_LOCKF_ROLOCK,
+    BDRV_LOCKF_UNLOCK,
+} BdrvLockfCmd;
+
 struct BlockDriver {
     const char *format_name;
     int instance_size;
@@ -317,6 +323,11 @@ struct BlockDriver {
      */
     void (*bdrv_drain)(BlockDriverState *bs);
 
+    /**
+     * Lock/unlock the image.
+     */
+    int (*bdrv_lockf)(BlockDriverState *bs, BdrvLockfCmd cmd);
+
     QLIST_ENTRY(BlockDriver) list;
 };
 
@@ -485,6 +496,7 @@ struct BlockDriverState {
     NotifierWithReturn write_threshold_notifier;
 
     int quiesce_counter;
+    bool image_locked;
 };
 
 struct BlockBackendRootState {
-- 
2.8.0