qapi: add dirty bitmap status

Bitmaps can be in a handful of different states with potentially
more to come as we tool around with migration and persistence patches.

Management applications may need to know why certain bitmaps are
unavailable for various commands, e.g. busy in another operation,
busy being migrated, etc.

Right now, all we offer is BlockDirtyInfo's boolean member 'frozen'.
Instead of adding more booleans, replace it by an enumeration member
'status' with values 'active' and 'frozen'.  Then add new value
'disabled'.

Incompatible change.  Fine because the changed part hasn't been
released so far.
Suggested-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NJohn Snow <jsnow@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
[Commit message tweaked]
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

block.c

@@ -3116,6 +3116,17 @@ bool bdrv_dirty_bitmap_enabled(BdrvDirtyBitmap *bitmap)
     return !(bitmap->disabled || bitmap->successor);
 }
 
+DirtyBitmapStatus bdrv_dirty_bitmap_status(BdrvDirtyBitmap *bitmap)
+{
+    if (bdrv_dirty_bitmap_frozen(bitmap)) {
+        return DIRTY_BITMAP_STATUS_FROZEN;
+    } else if (!bdrv_dirty_bitmap_enabled(bitmap)) {
+        return DIRTY_BITMAP_STATUS_DISABLED;
+    } else {
+        return DIRTY_BITMAP_STATUS_ACTIVE;
+    }
+}
+
 /**
  * Create a successor bitmap destined to replace this bitmap after an operation.
  * Requires that the bitmap is not frozen and has no successor.
@@ -3256,7 +3267,7 @@ BlockDirtyInfoList *bdrv_query_dirty_bitmaps(BlockDriverState *bs)
         info->granularity = bdrv_dirty_bitmap_granularity(bm);
         info->has_name = !!bm->name;
         info->name = g_strdup(bm->name);
-        info->frozen = bdrv_dirty_bitmap_frozen(bm);
+        info->status = bdrv_dirty_bitmap_status(bm);
         entry->value = info;
         *plist = entry;
         plist = &entry->next;

include/block/block.h

@@ -476,6 +476,7 @@ uint32_t bdrv_get_default_bitmap_granularity(BlockDriverState *bs);
 uint32_t bdrv_dirty_bitmap_granularity(BdrvDirtyBitmap *bitmap);
 bool bdrv_dirty_bitmap_enabled(BdrvDirtyBitmap *bitmap);
 bool bdrv_dirty_bitmap_frozen(BdrvDirtyBitmap *bitmap);
+DirtyBitmapStatus bdrv_dirty_bitmap_status(BdrvDirtyBitmap *bitmap);
 int bdrv_get_dirty(BlockDriverState *bs, BdrvDirtyBitmap *bitmap, int64_t sector);
 void bdrv_set_dirty_bitmap(BdrvDirtyBitmap *bitmap,
                            int64_t cur_sector, int nr_sectors);

qapi/block-core.json

@@ -325,6 +325,25 @@
   'data': { 'start': 'int', 'length': 'int', 'depth': 'int', 'zero': 'bool',
             'data': 'bool', '*offset': 'int' } }
 
+##
+# @DirtyBitmapStatus:
+#
+# An enumeration of possible states that a dirty bitmap can report to the user.
+#
+# @frozen: The bitmap is currently in-use by a backup operation or block job,
+#          and is immutable.
+#
+# @disabled: The bitmap is currently in-use by an internal operation and is
+#            read-only. It can still be deleted.
+#
+# @active: The bitmap is actively monitoring for new writes, and can be cleared,
+#          deleted, or used for backup operations.
+#
+# Since: 2.4
+##
+{ 'enum': 'DirtyBitmapStatus',
+  'data': ['active', 'disabled', 'frozen'] }
+
 ##
 # @BlockDirtyInfo:
 #
@@ -336,13 +355,13 @@
 #
 # @granularity: granularity of the dirty bitmap in bytes (since 1.4)
 #
-# @frozen: whether the dirty bitmap is frozen (Since 2.4)
+# @status: current status of the dirty bitmap (since 2.4)
 #
 # Since: 1.3
 ##
 { 'struct': 'BlockDirtyInfo',
   'data': {'*name': 'str', 'count': 'int', 'granularity': 'uint32',
-           'frozen': 'bool'} }
+           'status': 'DirtyBitmapStatus'} }
 
 ##
 # @BlockInfo: