block: Mark bdrv_has_zero_init() and callers GRAPH_RDLOCK

This adds GRAPH_RDLOCK annotations to declare that callers of
bdrv_has_zero_init() need to hold a reader lock for the graph because
it calls bdrv_filter_bs(), which accesses bs->file/backing.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20231027155333.420094-3-kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -6587,7 +6587,7 @@ int bdrv_has_zero_init_1(BlockDriverState *bs)
     return 1;
 }
 
-int bdrv_has_zero_init(BlockDriverState *bs)
+int coroutine_mixed_fn bdrv_has_zero_init(BlockDriverState *bs)
 {
     BlockDriverState *filtered;
     GLOBAL_STATE_CODE();

block/qcow2.c

@@ -5302,7 +5302,8 @@ static ImageInfoSpecific *qcow2_get_specific_info(BlockDriverState *bs,
     return spec_info;
 }
 
-static int coroutine_mixed_fn qcow2_has_zero_init(BlockDriverState *bs)
+static int coroutine_mixed_fn GRAPH_RDLOCK
+qcow2_has_zero_init(BlockDriverState *bs)
 {
     BDRVQcow2State *s = bs->opaque;
     bool preallocated;

block/raw-format.c

@@ -452,7 +452,7 @@ raw_co_ioctl(BlockDriverState *bs, unsigned long int req, void *buf)
     return bdrv_co_ioctl(bs->file->bs, req, buf);
 }
 
-static int raw_has_zero_init(BlockDriverState *bs)
+static int GRAPH_RDLOCK raw_has_zero_init(BlockDriverState *bs)
 {
     return bdrv_has_zero_init(bs->file->bs);
 }

block/vdi.c

@@ -990,7 +990,7 @@ static void vdi_close(BlockDriverState *bs)
     migrate_del_blocker(&s->migration_blocker);
 }
 
-static int vdi_has_zero_init(BlockDriverState *bs)
+static int GRAPH_RDLOCK vdi_has_zero_init(BlockDriverState *bs)
 {
     BDRVVdiState *s = bs->opaque;
 

block/vhdx.c

@@ -1695,7 +1695,7 @@ exit:
  *  Fixed images: default state of the BAT is fully populated, with
  *                file offsets and state PAYLOAD_BLOCK_FULLY_PRESENT.
  */
-static int coroutine_fn
+static int coroutine_fn GRAPH_UNLOCKED
 vhdx_create_bat(BlockBackend *blk, BDRVVHDXState *s,
                 uint64_t image_size, VHDXImageType type,
                 bool use_zero_blocks, uint64_t file_offset,
@@ -1708,6 +1708,7 @@ vhdx_create_bat(BlockBackend *blk, BDRVVHDXState *s,
     uint64_t unused;
     int block_state;
     VHDXSectorInfo sinfo;
+    bool has_zero_init;
 
     assert(s->bat == NULL);
 
@@ -1737,9 +1738,13 @@ vhdx_create_bat(BlockBackend *blk, BDRVVHDXState *s,
         goto exit;
     }
 
+    bdrv_graph_co_rdlock();
+    has_zero_init = bdrv_has_zero_init(blk_bs(blk));
+    bdrv_graph_co_rdunlock();
+
     if (type == VHDX_TYPE_FIXED ||
                 use_zero_blocks ||
-                bdrv_has_zero_init(blk_bs(blk)) == 0) {
+                has_zero_init == 0) {
         /* for a fixed file, the default BAT entry is not zero */
         s->bat = g_try_malloc0(length);
         if (length && s->bat == NULL) {
@@ -1782,7 +1787,7 @@ exit:
  * to create the BAT itself, we will also cause the BAT to be
  * created.
  */
-static int coroutine_fn
+static int coroutine_fn GRAPH_UNLOCKED
 vhdx_create_new_region_table(BlockBackend *blk, uint64_t image_size,
                              uint32_t block_size, uint32_t sector_size,
                              uint32_t log_size, bool use_zero_blocks,
@@ -2173,7 +2178,7 @@ static int coroutine_fn vhdx_co_check(BlockDriverState *bs,
     return 0;
 }
 
-static int vhdx_has_zero_init(BlockDriverState *bs)
+static int GRAPH_RDLOCK vhdx_has_zero_init(BlockDriverState *bs)
 {
     BDRVVHDXState *s = bs->opaque;
     int state;

block/vmdk.c

@@ -2894,7 +2894,7 @@ vmdk_co_get_allocated_file_size(BlockDriverState *bs)
     return ret;
 }
 
-static int vmdk_has_zero_init(BlockDriverState *bs)
+static int GRAPH_RDLOCK vmdk_has_zero_init(BlockDriverState *bs)
 {
     int i;
     BDRVVmdkState *s = bs->opaque;

block/vpc.c

@@ -1170,7 +1170,7 @@ fail:
 }
 
 
-static int vpc_has_zero_init(BlockDriverState *bs)
+static int GRAPH_RDLOCK vpc_has_zero_init(BlockDriverState *bs)
 {
     BDRVVPCState *s = bs->opaque;
 

blockdev.c

@@ -3156,9 +3156,11 @@ void qmp_drive_mirror(DriveMirror *arg, Error **errp)
         return;
     }
 
+    bdrv_graph_rdlock_main_loop();
     zero_target = (arg->sync == MIRROR_SYNC_MODE_FULL &&
                    (arg->mode == NEW_IMAGE_MODE_EXISTING ||
                     !bdrv_has_zero_init(target_bs)));
+    bdrv_graph_rdunlock_main_loop();
 
 
     /* Honor bdrv_try_change_aio_context() context acquisition requirements. */

include/block/block-global-state.h

@@ -189,7 +189,7 @@ void bdrv_drain_all(void);
 void bdrv_aio_cancel(BlockAIOCB *acb);
 
 int bdrv_has_zero_init_1(BlockDriverState *bs);
-int bdrv_has_zero_init(BlockDriverState *bs);
+int coroutine_mixed_fn GRAPH_RDLOCK bdrv_has_zero_init(BlockDriverState *bs);
 BlockDriverState *bdrv_find_node(const char *node_name);
 BlockDeviceInfoList *bdrv_named_nodes_list(bool flat, Error **errp);
 XDbgBlockGraph * GRAPH_RDLOCK bdrv_get_xdbg_block_graph(Error **errp);

include/block/block_int-common.h

@@ -349,7 +349,7 @@ struct BlockDriver {
      * Returns 1 if newly created images are guaranteed to contain only
      * zeros, 0 otherwise.
      */
-    int (*bdrv_has_zero_init)(BlockDriverState *bs);
+    int GRAPH_RDLOCK_PTR (*bdrv_has_zero_init)(BlockDriverState *bs);
 
     /*
      * Remove fd handlers, timers, and other event loop callbacks so the event

qemu-img.c

@@ -2099,7 +2099,9 @@ static int convert_do_copy(ImgConvertState *s)
     /* Check whether we have zero initialisation or can get it efficiently */
     if (!s->has_zero_init && s->target_is_new && s->min_sparse &&
         !s->target_has_backing) {
+        bdrv_graph_rdlock_main_loop();
         s->has_zero_init = bdrv_has_zero_init(blk_bs(s->target));
+        bdrv_graph_rdunlock_main_loop();
     }
 
     /* Allocate buffer for copied data. For compressed images, only one cluster