Commit c9ceb3ec authored Nov 23, 2017 by Max Reitz

qcow2: No persistent dirty bitmaps for compat=0.10



Persistent dirty bitmaps require a properly functioning
autoclear_features field, or we cannot track when an unsupporting
program might overwrite them.  Therefore, we cannot support them for
compat=0.10 images.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20171123020832.8165-3-mreitz@redhat.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

parent 3c363575

block/qcow2-bitmap.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -1449,6 +1449,16 @@ bool qcow2_can_store_new_dirty_bitmap(BlockDriverState *bs,
		bool found;
		Qcow2BitmapList *bm_list;

		if (s->qcow_version < 3) {
		/* Without autoclear_features, we would always have to assume
		* that a program without persistent dirty bitmap support has
		* accessed this qcow2 file when opening it, and would thus
		* have to drop all dirty bitmaps (defeating their purpose).
		*/
		error_setg(errp, "Cannot store dirty bitmaps in qcow2 v2 files");
		goto fail;
		}

		if (check_constraints_on_bitmap(bs, name, granularity, errp) != 0) {
		goto fail;
		}

block/qcow2.c

+11 −3

Original line number	Diff line number	Diff line
		@@ -302,9 +302,17 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
		}

		if (!(s->autoclear_features & QCOW2_AUTOCLEAR_BITMAPS)) {
		if (s->qcow_version < 3) {
		/* Let's be a bit more specific */
		warn_report("This qcow2 v2 image contains bitmaps, but "
		"they may have been modified by a program "
		"without persistent bitmap support; so now "
		"they must all be considered inconsistent");
		} else {
		warn_report("a program lacking bitmap support "
		"modified this file, so all bitmaps are now "
		"considered inconsistent");
		}
		error_printf("Some clusters may be leaked, "
		"run 'qemu-img check -r' on the image "
		"file to fix.");