[Qemu-devel] [PATCH] qcow2: Define and use QCOW2_COMPRESSED_SECTOR_SIZE

[Alberto Garcia <berto@igalia.com>]

When an L2 table entry points to a compressed cluster the space used
by the data is specified in 512-byte sectors. This size is independent
from BDRV_SECTOR_SIZE and is specific to the qcow2 file format.

The QCOW2_COMPRESSED_SECTOR_SIZE constant defined in this patch makes
this explicit.

Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 block/qcow2-cluster.c  |  5 +++--
 block/qcow2-refcount.c | 25 ++++++++++++++-----------
 block/qcow2.c          |  3 ++-
 block/qcow2.h          |  4 ++++
 4 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 974a4e8656..b36f4aa84a 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -796,8 +796,9 @@ int qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
         return cluster_offset;
     }
 
-    nb_csectors = ((cluster_offset + compressed_size - 1) >> 9) -
-                  (cluster_offset >> 9);
+    nb_csectors =
+        (cluster_offset + compressed_size - 1) / QCOW2_COMPRESSED_SECTOR_SIZE -
+        (cluster_offset / QCOW2_COMPRESSED_SECTOR_SIZE);
 
     cluster_offset |= QCOW_OFLAG_COMPRESSED |
                       ((uint64_t)nb_csectors << s->csize_shift);
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index fa7ac1f7cb..780bd49a00 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1172,12 +1172,11 @@ void qcow2_free_any_clusters(BlockDriverState *bs, uint64_t l2_entry,
     switch (ctype) {
     case QCOW2_CLUSTER_COMPRESSED:
         {
-            int nb_csectors;
-            nb_csectors = ((l2_entry >> s->csize_shift) &
-                           s->csize_mask) + 1;
-            qcow2_free_clusters(bs,
-                (l2_entry & s->cluster_offset_mask) & ~511,
-                nb_csectors * 512, type);
+            int64_t offset = (l2_entry & s->cluster_offset_mask)
+                & QCOW2_COMPRESSED_SECTOR_MASK;
+            int size = QCOW2_COMPRESSED_SECTOR_SIZE *
+                (((l2_entry >> s->csize_shift) & s->csize_mask) + 1);
+            qcow2_free_clusters(bs, offset, size, type);
         }
         break;
     case QCOW2_CLUSTER_NORMAL:
@@ -1317,9 +1316,12 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
                         nb_csectors = ((entry >> s->csize_shift) &
                                        s->csize_mask) + 1;
                         if (addend != 0) {
+                            uint64_t coffset = (entry & s->cluster_offset_mask)
+                                & QCOW2_COMPRESSED_SECTOR_MASK;
                             ret = update_refcount(
-                                bs, (entry & s->cluster_offset_mask) & ~511,
-                                nb_csectors * 512, abs(addend), addend < 0,
+                                bs, coffset,
+                                nb_csectors * QCOW2_COMPRESSED_SECTOR_SIZE,
+                                abs(addend), addend < 0,
                                 QCOW2_DISCARD_SNAPSHOT);
                             if (ret < 0) {
                                 goto fail;
@@ -1635,9 +1637,10 @@ static int check_refcounts_l2(BlockDriverState *bs, BdrvCheckResult *res,
             nb_csectors = ((l2_entry >> s->csize_shift) &
                            s->csize_mask) + 1;
             l2_entry &= s->cluster_offset_mask;
-            ret = qcow2_inc_refcounts_imrt(bs, res,
-                                           refcount_table, refcount_table_size,
-                                           l2_entry & ~511, nb_csectors * 512);
+            ret = qcow2_inc_refcounts_imrt(
+                bs, res, refcount_table, refcount_table_size,
+                l2_entry & QCOW2_COMPRESSED_SECTOR_MASK,
+                nb_csectors * QCOW2_COMPRESSED_SECTOR_SIZE);
             if (ret < 0) {
                 goto fail;
             }
diff --git a/block/qcow2.c b/block/qcow2.c
index a520d116ef..80679a84d2 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -4188,7 +4188,8 @@ qcow2_co_preadv_compressed(BlockDriverState *bs,
 
     coffset = file_cluster_offset & s->cluster_offset_mask;
     nb_csectors = ((file_cluster_offset >> s->csize_shift) & s->csize_mask) + 1;
-    csize = nb_csectors * 512 - (coffset & 511);
+    csize = nb_csectors * QCOW2_COMPRESSED_SECTOR_SIZE -
+        (coffset & ~QCOW2_COMPRESSED_SECTOR_MASK);
 
     buf = g_try_malloc(csize);
     if (!buf) {
diff --git a/block/qcow2.h b/block/qcow2.h
index fdee297f33..7e796877d6 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -74,6 +74,10 @@
 #define MIN_CLUSTER_BITS 9
 #define MAX_CLUSTER_BITS 21
 
+/* Defined in the qcow2 spec (compressed cluster descriptor) */
+#define QCOW2_COMPRESSED_SECTOR_SIZE 512U
+#define QCOW2_COMPRESSED_SECTOR_MASK (~(QCOW2_COMPRESSED_SECTOR_SIZE - 1))
+
 /* Must be at least 2 to cover COW */
 #define MIN_L2_CACHE_SIZE 2 /* cache entries */
 
-- 
2.11.0