[Qemu-devel] [PATCH 13/29] qcow2: add dirty bitmaps extension

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

Add dirty bitmap extension as specified in docs/specs/qcow2.txt.

Load bitmap headers on open. Handle close and update_header.

Handle resize: just delete all bitmaps from the image. Not loaded
bitmaps will be lost (for now - all except autoloading ones). This may
be fixed in future.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/qcow2-bitmap.c |  8 +++++
 block/qcow2.c        | 93 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 101 insertions(+)

diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
index 92d95c5..a34cfe8 100644
--- a/block/qcow2-bitmap.c
+++ b/block/qcow2-bitmap.c
@@ -68,6 +68,14 @@ static inline bool can_write(BlockDriverState *bs)
     return !bdrv_is_read_only(bs) && !(bdrv_get_flags(bs) & BDRV_O_INACTIVE);
 }
 
+void qcow2_free_bitmaps(BlockDriverState *bs)
+{
+    BDRVQcow2State *s = bs->opaque;
+
+    g_free(s->bitmap_directory);
+    s->bitmap_directory = NULL;
+}
+
 static inline void bitmap_header_to_cpu(QCow2BitmapHeader *h)
 {
     be64_to_cpus(&h->bitmap_table_offset);
diff --git a/block/qcow2.c b/block/qcow2.c
index bad7b83..3e9b47e 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -63,6 +63,7 @@ typedef struct {
 #define  QCOW2_EXT_MAGIC_END 0
 #define  QCOW2_EXT_MAGIC_BACKING_FORMAT 0xE2792ACA
 #define  QCOW2_EXT_MAGIC_FEATURE_TABLE 0x6803f857
+#define  QCOW2_EXT_MAGIC_DIRTY_BITMAPS 0x23852875
 
 static int qcow2_probe(const uint8_t *buf, int buf_size, const char *filename)
 {
@@ -92,6 +93,7 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
     QCowExtension ext;
     uint64_t offset;
     int ret;
+    Qcow2BitmapHeaderExt bitmaps_ext;
 
 #ifdef DEBUG_EXT
     printf("qcow2_read_extensions: start=%ld end=%ld\n", start_offset, end_offset);
@@ -162,6 +164,67 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
             }
             break;
 
+        case QCOW2_EXT_MAGIC_DIRTY_BITMAPS:
+            ret = bdrv_pread(bs->file, offset, &bitmaps_ext, ext.len);
+            if (ret < 0) {
+                error_setg_errno(errp, -ret, "ERROR: bitmaps_ext: "
+                                 "Could not read ext header");
+                return ret;
+            }
+
+            if (bitmaps_ext.reserved32 != 0) {
+                error_setg_errno(errp, -ret, "ERROR: bitmaps_ext: "
+                                 "Reserved field is not zero.");
+                return -EINVAL;
+            }
+
+            be32_to_cpus(&bitmaps_ext.nb_bitmaps);
+            be64_to_cpus(&bitmaps_ext.bitmap_directory_size);
+            be64_to_cpus(&bitmaps_ext.bitmap_directory_offset);
+
+            if (bitmaps_ext.nb_bitmaps > QCOW_MAX_DIRTY_BITMAPS) {
+                error_setg(errp, "ERROR: bitmaps_ext: "
+                                 "too many dirty bitmaps");
+                return -EINVAL;
+            }
+
+            if (bitmaps_ext.nb_bitmaps == 0) {
+                error_setg(errp, "ERROR: bitmaps_ext: "
+                                 "found bitmaps extension with zero bitmaps");
+                return -EINVAL;
+            }
+
+            if (bitmaps_ext.bitmap_directory_offset & (s->cluster_size - 1)) {
+                error_setg(errp, "ERROR: bitmaps_ext: "
+                                 "wrong dirty bitmap directory offset");
+                return -EINVAL;
+            }
+
+            if (bitmaps_ext.bitmap_directory_size >
+                QCOW_MAX_DIRTY_BITMAP_DIRECTORY_SIZE) {
+                error_setg(errp, "ERROR: bitmaps_ext: "
+                                 "too large dirty bitmap directory");
+                return -EINVAL;
+            }
+
+            s->nb_bitmaps = bitmaps_ext.nb_bitmaps;
+            s->bitmap_directory_offset =
+                    bitmaps_ext.bitmap_directory_offset;
+            s->bitmap_directory_size =
+                    bitmaps_ext.bitmap_directory_size;
+
+            ret = qcow2_read_bitmaps(bs, errp);
+            if (ret < 0) {
+                return ret;
+            }
+
+#ifdef DEBUG_EXT
+            printf("Qcow2: Got dirty bitmaps extension:"
+                   " offset=%" PRIu64 " nb_bitmaps=%" PRIu32 "\n",
+                   s->bitmap_directory_offset, s->nb_bitmaps);
+#endif
+            break;
+
         default:
             /* unknown magic - save it in case we need to rewrite the header */
             {
@@ -1179,6 +1242,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
     g_free(s->unknown_header_fields);
     cleanup_unknown_header_ext(bs);
     qcow2_free_snapshots(bs);
+    qcow2_free_bitmaps(bs);
     qcow2_refcount_close(bs);
     qemu_vfree(s->l1_table);
     /* else pre-write overlap checks in cache_destroy may crash */
@@ -1749,6 +1813,7 @@ static void qcow2_close(BlockDriverState *bs)
     qemu_vfree(s->cluster_data);
     qcow2_refcount_close(bs);
     qcow2_free_snapshots(bs);
+    qcow2_free_bitmaps(bs);
 }
 
 static void qcow2_invalidate_cache(BlockDriverState *bs, Error **errp)
@@ -1939,6 +2004,24 @@ int qcow2_update_header(BlockDriverState *bs)
         buflen -= ret;
     }
 
+    if (s->nb_bitmaps > 0) {
+        Qcow2BitmapHeaderExt bitmaps_header = {
+            .nb_bitmaps = cpu_to_be32(s->nb_bitmaps),
+            .bitmap_directory_size =
+                    cpu_to_be64(s->bitmap_directory_size),
+            .bitmap_directory_offset =
+                    cpu_to_be64(s->bitmap_directory_offset)
+        };
+        ret = header_ext_add(buf, QCOW2_EXT_MAGIC_DIRTY_BITMAPS,
+                             &bitmaps_header, sizeof(bitmaps_header),
+                             buflen);
+        if (ret < 0) {
+            goto fail;
+        }
+        buf += ret;
+        buflen -= ret;
+    }
+
     /* Keep unknown header extensions */
     QLIST_FOREACH(uext, &s->unknown_header_ext, next) {
         ret = header_ext_add(buf, uext->magic, uext->data, uext->len, buflen);
@@ -2509,6 +2592,16 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset)
         return -ENOTSUP;
     }
 
+    /* cannot proceed if image has bitmaps */
+    if (s->nb_bitmaps) {
+        /* FIXME: not loaded bitmaps will be lost */
+        ret = qcow2_delete_bitmaps(bs);
+        if (ret < 0) {
+            error_report("Can't remove bitmaps from qcow2 on truncate");
+            return ret;
+        }
+    }
+
     /* shrinking is currently not supported */
     if (offset < bs->total_sectors * 512) {
         error_report("qcow2 doesn't support shrinking images yet");
-- 
1.8.3.1