[Qemu-devel] [PATCH 07/21] qcow2: add dirty bitmaps extension

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

Add dirty bitmap extension as specified in docs/specs/qcow2.txt.
For now, just mirror extension header into Qcow2 state and check
constraints.

For now, disable image resize if it has bitmaps. It will be fixed later.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/qcow2.c | 101 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 block/qcow2.h |  24 ++++++++++++++
 2 files changed, 123 insertions(+), 2 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 6d5689a..c6050de 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 +164,75 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
             }
             break;
 
+        case QCOW2_EXT_MAGIC_DIRTY_BITMAPS:
+            if (ext.len != sizeof(bitmaps_ext)) {
+                error_setg_errno(errp, -ret, "ERROR: bitmaps_ext: "
+                                 "Invalid extension length");
+                return -EINVAL;
+            }
+
+            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, 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: "
+                                 "invalid 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;
+
+#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 */
             {
@@ -1144,8 +1215,9 @@ 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");
@@ -1944,6 +2016,24 @@ 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);
@@ -2514,6 +2604,13 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset)
         return -ENOTSUP;
     }
 
+    /* cannot proceed if image has bitmaps */
+    if (s->nb_bitmaps) {
+        /* TODO: resize bitmaps in the image */
+        error_report("Can't resize an image which has bitmaps");
+        return -ENOTSUP;
+    }
+
     /* shrinking is currently not supported */
     if (offset < bs->total_sectors * 512) {
         error_report("qcow2 doesn't support shrinking images yet");
diff --git a/block/qcow2.h b/block/qcow2.h
index 92203a8..be9ba32 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -52,6 +52,10 @@
  * space for snapshot names and IDs */
 #define QCOW_MAX_SNAPSHOTS_SIZE (1024 * QCOW_MAX_SNAPSHOTS)
 
+/* Bitmap header extension constraints */
+#define QCOW_MAX_DIRTY_BITMAPS 65535
+#define QCOW_MAX_DIRTY_BITMAP_DIRECTORY_SIZE (1024 * QCOW_MAX_DIRTY_BITMAPS)
+
 /* indicate that the refcount of the referenced cluster is exactly one. */
 #define QCOW_OFLAG_COPIED     (1ULL << 63)
 /* indicate that the cluster is compressed (they never have the copied flag) */
@@ -195,6 +199,15 @@ 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,
@@ -222,6 +235,13 @@ typedef uint64_t Qcow2GetRefcountFunc(const void *refcount_array,
 typedef void Qcow2SetRefcountFunc(void *refcount_array,
                                   uint64_t index, uint64_t value);
 
+typedef struct Qcow2BitmapHeaderExt {
+    uint32_t nb_bitmaps;
+    uint32_t reserved32;
+    uint64_t bitmap_directory_size;
+    uint64_t bitmap_directory_offset;
+} QEMU_PACKED Qcow2BitmapHeaderExt;
+
 typedef struct BDRVQcow2State {
     int cluster_bits;
     int cluster_size;
@@ -263,6 +283,10 @@ typedef struct BDRVQcow2State {
     unsigned int nb_snapshots;
     QCowSnapshot *snapshots;
 
+    uint32_t nb_bitmaps;
+    uint64_t bitmap_directory_size;
+    uint64_t bitmap_directory_offset;
+
     int flags;
     int qcow_version;
     bool use_lazy_refcounts;
-- 
1.8.3.1