[Qemu-block] [PATCH v6 04/22] 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 <address@hidden>
---
 block.c                   | 57 +++++++++++++++++++++++++++++++++++++++++++++++
 include/block/block.h     | 11 ++++++++-
 include/block/block_int.h |  5 +++++
 3 files changed, 72 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 736432f..4c2a3ff 100644
--- a/block.c
+++ b/block.c
@@ -854,6 +854,50 @@ out:
     g_free(gen_node_name);
 }
 
+BdrvLockfCmd bdrv_get_locking_cmd(int flags)
+{
+    if (flags & BDRV_O_NO_LOCK) {
+        return BDRV_LOCKF_UNLOCK;
+    } else if (flags & BDRV_O_SHARED_LOCK) {
+        return BDRV_LOCKF_SHARED;
+    } else if (flags & BDRV_O_RDWR) {
+        return BDRV_LOCKF_EXCLUSIVE;
+    } else {
+        return BDRV_LOCKF_SHARED;
+    }
+}
+
+static int bdrv_lock_unlock_image_do(BlockDriverState *bs, BdrvLockfCmd cmd)
+{
+    int ret;
+
+    if (bs->cur_lock == cmd) {
+        return 0;
+    } else if (!bs->drv) {
+        return -ENOMEDIUM;
+    } else if (!bs->drv->bdrv_lockf) {
+        return 0;
+    }
+    ret = bs->drv->bdrv_lockf(bs, cmd);
+    if (ret == -ENOTSUP) {
+        /* Handle it the same way as !bs->drv->bdrv_lockf */
+        ret = 0;
+    } else if (ret == 0) {
+        bs->cur_lock = cmd;
+    }
+    return ret;
+}
+
+static int bdrv_lock_image(BlockDriverState *bs)
+{
+    return bdrv_lock_unlock_image_do(bs, bdrv_get_locking_cmd(bs->open_flags));
+}
+
+static int bdrv_unlock_image(BlockDriverState *bs)
+{
+    return bdrv_lock_unlock_image_do(bs, BDRV_LOCKF_UNLOCK);
+}
+
 static QemuOptsList bdrv_runtime_opts = {
     .name = "bdrv_common",
     .head = QTAILQ_HEAD_INITIALIZER(bdrv_runtime_opts.head),
@@ -1003,6 +1047,14 @@ 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");
@@ -2164,6 +2216,7 @@ static void bdrv_close(BlockDriverState *bs)
     if (bs->drv) {
         BdrvChild *child, *next;
 
+        bdrv_unlock_image(bs);
         bs->drv->bdrv_close(bs);
         bs->drv = NULL;
 
@@ -3187,6 +3240,9 @@ 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)
@@ -3229,6 +3285,7 @@ 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.h b/include/block/block.h
index 02b598b..782ef2f 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -183,6 +183,15 @@ typedef enum BlockOpType {
     BLOCK_OP_TYPE_MAX,
 } BlockOpType;
 
+typedef enum {
+    /* The values are ordered so that lower number implies higher restriction.
+     * Starting from 1 to make 0 an invalid value.
+     * */
+    BDRV_LOCKF_EXCLUSIVE = 1,
+    BDRV_LOCKF_SHARED,
+    BDRV_LOCKF_UNLOCK,
+} BdrvLockfCmd;
+
 void bdrv_info_print(Monitor *mon, const QObject *data);
 void bdrv_info(Monitor *mon, QObject **ret_data);
 void bdrv_stats_print(Monitor *mon, const QObject *data);
@@ -274,7 +283,7 @@ int bdrv_drop_intermediate(BlockDriverState *active, 
BlockDriverState *top,
 BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
                                     BlockDriverState *bs);
 BlockDriverState *bdrv_find_base(BlockDriverState *bs);
-
+BdrvLockfCmd bdrv_get_locking_cmd(int flags);
 
 typedef struct BdrvCheckResult {
     int corruptions;
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 30a9717..29cc632 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -317,6 +317,10 @@ 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;
 };
@@ -500,6 +504,7 @@ struct BlockDriverState {
     unsigned io_plug_disabled;
 
     int quiesce_counter;
+    BdrvLockfCmd cur_lock;
 };
 
 struct BlockBackendRootState {
-- 
2.8.2