[Qemu-devel] [PATCH v5 04/27] block: Introduce image file locking

[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                   | 48 +++++++++++++++++++++++++++++++++++++++++++++++
 include/block/block_int.h | 11 +++++++++++
 2 files changed, 59 insertions(+)

diff --git a/block.c b/block.c
index 18a497f..153f9d2 100644
--- a/block.c
+++ b/block.c
@@ -844,6 +844,41 @@ out:
     g_free(gen_node_name);
 }
 
+static int bdrv_lock_unlock_image_do(BlockDriverState *bs, bool lock_image)
+{
+    int cmd = BDRV_LOCKF_UNLOCK;
+    int ret;
+
+    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) &&
+              !(bs->open_flags & BDRV_O_SHARED_LOCK) ? BDRV_LOCKF_EXCLUSIVE :
+                                                       BDRV_LOCKF_SHARED;
+    }
+    ret = bs->drv->bdrv_lockf(bs, cmd);
+    if (ret == -ENOTSUP) {
+        /* Handle it the same way as !bs->drv->bdrv_lockf */
+        ret = 0;
+    }
+    return ret;
+}
+
+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),
@@ -993,6 +1028,14 @@ 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");
@@ -2142,6 +2185,7 @@ static void bdrv_close(BlockDriverState *bs)
     if (bs->drv) {
         BdrvChild *child, *next;
 
+        bdrv_unlock_image(bs);
         bs->drv->bdrv_close(bs);
         bs->drv = NULL;
 
@@ -3235,6 +3279,9 @@ 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)
@@ -3276,6 +3323,7 @@ static int bdrv_inactivate_recurse(BlockDriverState *bs,
     }
 
     if (setting_flag) {
+        ret = bdrv_unlock_image(bs);
         bs->open_flags |= BDRV_O_INACTIVE;
     }
     return 0;
diff --git a/include/block/block_int.h b/include/block/block_int.h
index a029c20..2b82d49 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_EXCLUSIVE,
+    BDRV_LOCKF_SHARED,
+    BDRV_LOCKF_UNLOCK,
+} BdrvLockfCmd;
+
 struct BlockDriver {
     const char *format_name;
     int instance_size;
@@ -318,6 +324,10 @@ struct BlockDriver {
                            Error **errp);
     void (*bdrv_del_child)(BlockDriverState *parent, BdrvChild *child,
                            Error **errp);
+    /**
+     * Lock/unlock the image.
+     */
+    int (*bdrv_lockf)(BlockDriverState *bs, BdrvLockfCmd cmd);
 
     QLIST_ENTRY(BlockDriver) list;
 };
@@ -496,6 +506,7 @@ struct BlockDriverState {
     unsigned io_plug_disabled;
 
     int quiesce_counter;
+    bool image_locked;
 };
 
 struct BlockBackendRootState {
-- 
2.8.2