bitmap: Enforce maximum bitmap name length

We document that for qcow2 persistent bitmaps, the name cannot exceed
1023 bytes.  It is inconsistent if transient bitmaps do not have to
abide by the same limit, and it is unlikely that any existing client
even cares about using bitmap names this long.  It's time to codify
that ALL bitmaps managed by qemu (whether persistent in qcow2 or not)
have a documented maximum length.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20191114024635.11363-3-eblake@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

block/dirty-bitmap.c

@@ -104,9 +104,15 @@ BdrvDirtyBitmap *bdrv_create_dirty_bitmap(BlockDriverState *bs,
 
     assert(is_power_of_2(granularity) && granularity >= BDRV_SECTOR_SIZE);
 
-    if (name && bdrv_find_dirty_bitmap(bs, name)) {
-        error_setg(errp, "Bitmap already exists: %s", name);
-        return NULL;
+    if (name) {
+        if (bdrv_find_dirty_bitmap(bs, name)) {
+            error_setg(errp, "Bitmap already exists: %s", name);
+            return NULL;
+        }
+        if (strlen(name) > BDRV_BITMAP_MAX_NAME_SIZE) {
+            error_setg(errp, "Bitmap name too long: %s", name);
+            return NULL;
+        }
     }
     bitmap_size = bdrv_getlength(bs);
     if (bitmap_size < 0) {

block/qcow2-bitmap.c

@@ -42,6 +42,8 @@
 #define BME_MIN_GRANULARITY_BITS 9
 #define BME_MAX_NAME_SIZE 1023
 
+QEMU_BUILD_BUG_ON(BME_MAX_NAME_SIZE != BDRV_BITMAP_MAX_NAME_SIZE);
+
 #if BME_MAX_TABLE_SIZE * 8ULL > INT_MAX
 #error In the code bitmap table physical size assumed to fit into int
 #endif

include/block/dirty-bitmap.h

@@ -14,6 +14,8 @@ typedef enum BitmapCheckFlags {
                              BDRV_BITMAP_INCONSISTENT)
 #define BDRV_BITMAP_ALLOW_RO (BDRV_BITMAP_BUSY | BDRV_BITMAP_INCONSISTENT)
 
+#define BDRV_BITMAP_MAX_NAME_SIZE 1023
+
 BdrvDirtyBitmap *bdrv_create_dirty_bitmap(BlockDriverState *bs,
                                           uint32_t granularity,
                                           const char *name,

qapi/block-core.json

@@ -2042,7 +2042,7 @@
 #
 # @node: name of device/node which the bitmap is tracking
 #
-# @name: name of the dirty bitmap
+# @name: name of the dirty bitmap (must be less than 1024 bytes)
 #
 # @granularity: the bitmap granularity, default is 64k for
 #               block-dirty-bitmap-add