[Qemu-devel] [PATCH 15/22] qcow2-dirty-bitmap: add autoclear bit

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

Add autoclear bit for handling rewriting image by old qemu version.

If autoclear bit is not set, but bitmaps extension is found it
would not be loaded and warning will be generated.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/qcow2-dirty-bitmap.c |  4 ++++
 block/qcow2.c              | 12 ++++++++++--
 block/qcow2.h              |  9 +++++++++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/block/qcow2-dirty-bitmap.c b/block/qcow2-dirty-bitmap.c
index 24415df..384ccea 100644
--- a/block/qcow2-dirty-bitmap.c
+++ b/block/qcow2-dirty-bitmap.c
@@ -419,6 +419,7 @@ static int directory_push_entry(BlockDriverState *bs, QCow2BitmapHeader *header)
     int64_t new_offset = 0, old_offset = 0;
     uint64_t new_size = s->bitmap_directory_size + entry_size, old_size = 0;
     void *p;
+    uint64_t old_autocl;
     int64_t nb_sectors = bdrv_nb_sectors(bs);
 
     if (nb_sectors < 0) {
@@ -437,6 +438,7 @@ static int directory_push_entry(BlockDriverState *bs, QCow2BitmapHeader *header)
 
     old_offset = s->bitmap_directory_offset;
     old_size = s->bitmap_directory_size;
+    old_autocl = s->autoclear_features;
 
     uint8_t *new_dir = g_try_malloc(new_size);
     if (new_dir == NULL) {
@@ -458,6 +460,7 @@ static int directory_push_entry(BlockDriverState *bs, QCow2BitmapHeader *header)
 
     s->bitmap_directory_offset = new_offset;
     s->bitmap_directory_size = new_size;
+    s->autoclear_features |= QCOW2_AUTOCLEAR_DIRTY_BITMAPS;
 
     ret = update_header_sync(bs);
     if (ret < 0) {
@@ -479,6 +482,7 @@ fail:
         qcow2_free_clusters(bs, new_offset, new_size, QCOW2_DISCARD_ALWAYS);
         s->bitmap_directory_offset = old_offset;
         s->bitmap_directory_size = old_size;
+        s->autoclear_features = old_autocl;
     }
 
     p = g_try_realloc(s->bitmap_directory, s->bitmap_directory_size);
diff --git a/block/qcow2.c b/block/qcow2.c
index 7a342c2..f269bab 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -164,6 +164,13 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
             break;
 
         case QCOW2_EXT_MAGIC_DIRTY_BITMAPS:
+            if (!(s->autoclear_features & QCOW2_AUTOCLEAR_DIRTY_BITMAPS)) {
+                fprintf(stderr,
+                        "WARNING: bitmaps_ext: autoclear flag is not "
+                        "set, all bitmaps will be considered as inconsistent");
+                break;
+            }
+
             ret = bdrv_pread(bs->file->bs, offset, &bitmaps_ext, ext.len);
             if (ret < 0) {
                 error_setg_errno(errp, -ret, "ERROR: bitmaps_ext: "
@@ -1205,8 +1212,9 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     /* Clear unknown autoclear feature bits */
-    if (!bs->read_only && !(flags & BDRV_O_INACTIVE) && s->autoclear_features) {
-        s->autoclear_features = 0;
+    if (!bs->read_only && !(flags & BDRV_O_INACTIVE) &&
+        (s->autoclear_features & ~QCOW2_AUTOCLEAR_MASK)) {
+        s->autoclear_features &= QCOW2_AUTOCLEAR_MASK;
         ret = qcow2_update_header(bs);
         if (ret < 0) {
             error_setg_errno(errp, -ret, "Could not update qcow2 header");
diff --git a/block/qcow2.h b/block/qcow2.h
index 423c279..63ea543 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -220,6 +220,15 @@ enum {
     QCOW2_COMPAT_FEAT_MASK            = QCOW2_COMPAT_LAZY_REFCOUNTS,
 };
 
+/* Autoclear feature bits */
+enum {
+    QCOW2_AUTOCLEAR_DIRTY_BITMAPS_BITNR = 0,
+    QCOW2_AUTOCLEAR_DIRTY_BITMAPS       =
+        1 << QCOW2_AUTOCLEAR_DIRTY_BITMAPS_BITNR,
+
+    QCOW2_AUTOCLEAR_MASK                = QCOW2_AUTOCLEAR_DIRTY_BITMAPS,
+};
+
 enum qcow2_discard_type {
     QCOW2_DISCARD_NEVER = 0,
     QCOW2_DISCARD_ALWAYS,
-- 
1.8.3.1