[PATCH v2] qcow2: Expose bitmaps' size during measure

[Eric Blake]

It's useful to know how much space can be occupied by qcow2 persistent
bitmaps, even though such metadata is unrelated to the guest-visible
data.  Report this value as an additional field.  Update iotest 190 to
cover it.

The addition of a new field demonstrates why we should always
zero-initialize qapi C structs; while the qcow2 driver still fully
populates all fields, the raw and crypto drivers had to be tweaked.

See also: https://bugzilla.redhat.com/1779904

Reported-by: Nir Soffer <address@hidden>
Signed-off-by: Eric Blake <address@hidden>
---

In v2:
- fix uninit memory [patchew]
- add BZ number [Nir]
- add iotest coverage

 qapi/block-core.json       | 15 ++++++++----
 block/crypto.c             |  2 +-
 block/qcow2.c              | 29 +++++++++++++++++++++-
 block/raw-format.c         |  2 +-
 qemu-img.c                 |  3 +++
 tests/qemu-iotests/190     | 50 ++++++++++++++++++++++++++++++++++++--
 tests/qemu-iotests/190.out | 20 ++++++++++++++-
 7 files changed, 110 insertions(+), 11 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 943df1926a91..b47c6d69ba27 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -633,18 +633,23 @@
 # efficiently so file size may be smaller than virtual disk size.
 #
 # The values are upper bounds that are guaranteed to fit the new image file.
-# Subsequent modification, such as internal snapshot or bitmap creation, may
-# require additional space and is not covered here.
+# Subsequent modification, such as internal snapshot or further bitmap
+# creation, may require additional space and is not covered here.
 #
-# @required: Size required for a new image file, in bytes.
+# @required: Size required for a new image file, in bytes, when copying just
+#            guest-visible contents.
 #
 # @fully-allocated: Image file size, in bytes, once data has been written
-#                   to all sectors.
+#                   to all sectors, when copying just guest-visible contents.
+#
+# @bitmaps: Additional size required for bitmap metadata not directly used
+#           for guest contents, when that metadata can be copied in addition
+#           to guest contents. (since 5.1)
 #
 # Since: 2.10
 ##
 { 'struct': 'BlockMeasureInfo',
-  'data': {'required': 'int', 'fully-allocated': 'int'} }
+  'data': {'required': 'int', 'fully-allocated': 'int', '*bitmaps': 'int'} }

 ##
 # @query-block:
diff --git a/block/crypto.c b/block/crypto.c
index d577f89659fa..4e0f3ec97f0e 100644
--- a/block/crypto.c
+++ b/block/crypto.c
@@ -535,7 +535,7 @@ static BlockMeasureInfo *block_crypto_measure(QemuOpts 
*opts,
      * Unallocated blocks are still encrypted so allocation status makes no
      * difference to the file size.
      */
-    info = g_new(BlockMeasureInfo, 1);
+    info = g_new0(BlockMeasureInfo, 1);
     info->fully_allocated = luks_payload_size + size;
     info->required = luks_payload_size + size;
     return info;
diff --git a/block/qcow2.c b/block/qcow2.c
index b524b0c53f84..9fd650928016 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -4657,6 +4657,7 @@ static BlockMeasureInfo *qcow2_measure(QemuOpts *opts, 
BlockDriverState *in_bs,
     PreallocMode prealloc;
     bool has_backing_file;
     bool has_luks;
+    uint64_t bitmaps_size = 0; /* size occupied by bitmaps in in_bs */

     /* Parse image creation options */
     cluster_size = qcow2_opt_get_cluster_size_del(opts, &local_err);
@@ -4732,6 +4733,8 @@ static BlockMeasureInfo *qcow2_measure(QemuOpts *opts, 
BlockDriverState *in_bs,

     /* Account for input image */
     if (in_bs) {
+        BdrvDirtyBitmap *bm;
+        size_t bitmap_overhead = 0;
         int64_t ssize = bdrv_getlength(in_bs);
         if (ssize < 0) {
             error_setg_errno(&local_err, -ssize,
@@ -4739,6 +4742,28 @@ static BlockMeasureInfo *qcow2_measure(QemuOpts *opts, 
BlockDriverState *in_bs,
             goto err;
         }

+        FOR_EACH_DIRTY_BITMAP(in_bs, bm) {
+            if (bdrv_dirty_bitmap_get_persistence(bm)) {
+                const char *name = bdrv_dirty_bitmap_name(bm);
+                uint32_t granularity = bdrv_dirty_bitmap_granularity(bm);
+                uint64_t bmbits = DIV_ROUND_UP(bdrv_dirty_bitmap_size(bm),
+                                               granularity);
+                uint64_t bmclusters = DIV_ROUND_UP(DIV_ROUND_UP(bmbits,
+                                                                CHAR_BIT),
+                                                   cluster_size);
+
+                /* Assume the entire bitmap is allocated */
+                bitmaps_size += bmclusters * cluster_size;
+                /* Also reserve space for the bitmap table entries */
+                bitmaps_size += ROUND_UP(bmclusters * sizeof(uint64_t),
+                                         cluster_size);
+                /* Guess at contribution to bitmap directory size */
+                bitmap_overhead += ROUND_UP(strlen(name) + 24,
+                                            sizeof(uint64_t));
+            }
+        }
+        bitmaps_size += ROUND_UP(bitmap_overhead, cluster_size);
+
         virtual_size = ROUND_UP(ssize, cluster_size);

         if (has_backing_file) {
@@ -4785,7 +4810,7 @@ static BlockMeasureInfo *qcow2_measure(QemuOpts *opts, 
BlockDriverState *in_bs,
         required = virtual_size;
     }

-    info = g_new(BlockMeasureInfo, 1);
+    info = g_new0(BlockMeasureInfo, 1);
     info->fully_allocated =
         qcow2_calc_prealloc_size(virtual_size, cluster_size,
                                  ctz32(refcount_bits)) + luks_payload_size;
@@ -4795,6 +4820,8 @@ static BlockMeasureInfo *qcow2_measure(QemuOpts *opts, 
BlockDriverState *in_bs,
      * still counted.
      */
     info->required = info->fully_allocated - virtual_size + required;
+    info->has_bitmaps = !!bitmaps_size;
+    info->bitmaps = bitmaps_size;
     return info;

 err:
diff --git a/block/raw-format.c b/block/raw-format.c
index 93b25e1b6b0b..4bb54f4ac6c5 100644
--- a/block/raw-format.c
+++ b/block/raw-format.c
@@ -346,7 +346,7 @@ static BlockMeasureInfo *raw_measure(QemuOpts *opts, 
BlockDriverState *in_bs,
                             BDRV_SECTOR_SIZE);
     }

-    info = g_new(BlockMeasureInfo, 1);
+    info = g_new0(BlockMeasureInfo, 1);
     info->required = required;

     /* Unallocated sectors count towards the file size in raw images */
diff --git a/qemu-img.c b/qemu-img.c
index 6541357179c2..d900bde89911 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -5084,6 +5084,9 @@ static int img_measure(int argc, char **argv)
     if (output_format == OFORMAT_HUMAN) {
         printf("required size: %" PRIu64 "\n", info->required);
         printf("fully allocated size: %" PRIu64 "\n", info->fully_allocated);
+        if (info->has_bitmaps) {
+            printf("bitmaps size: %" PRIu64 "\n", info->bitmaps);
+        }
     } else {
         dump_json_block_measure_info(info);
     }
diff --git a/tests/qemu-iotests/190 b/tests/qemu-iotests/190
index 6d41650438e1..15a1c8d4227a 100755
--- a/tests/qemu-iotests/190
+++ b/tests/qemu-iotests/190
@@ -2,7 +2,7 @@
 #
 # qemu-img measure sub-command tests on huge qcow2 files
 #
-# Copyright (C) 2017 Red Hat, Inc.
+# Copyright (C) 2017-2020 Red Hat, Inc.
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -42,7 +42,19 @@ trap "_cleanup; exit \$status" 0 1 2 3 15
 _supported_fmt qcow2
 _supported_proto file

-echo "== Huge file =="
+do_run_qemu()
+{
+    echo Testing: "$@"
+    $QEMU -nographic -qmp stdio -serial none "$@"
+    echo
+}
+
+run_qemu()
+{
+    do_run_qemu "$@" 2>&1 | _filter_testdir | _filter_qmp
+}
+
+echo "== Huge file without bitmaps =="
 echo

 _make_test_img -o 'cluster_size=2M' 2T
@@ -51,6 +63,40 @@ $QEMU_IMG measure -O raw -f qcow2 "$TEST_IMG"
 $QEMU_IMG measure -O qcow2 -o cluster_size=64k -f qcow2 "$TEST_IMG"
 $QEMU_IMG measure -O qcow2 -o cluster_size=2M -f qcow2 "$TEST_IMG"

+echo
+echo "== Huge file with bitmaps =="
+echo
+
+run_qemu -blockdev \
+    driver=qcow2,node-name=n,file.driver=file,file.filename="$TEST_IMG" <<EOF
+{ "execute": "qmp_capabilities" }
+{ "execute": "transaction",
+  "arguments": {
+    "actions": [
+      { "type": "block-dirty-bitmap-add",
+        "data": {
+          "node": "n",
+          "name": "b1",
+          "persistent": true,
+          "granularity": 512
+        } },
+      { "type": "block-dirty-bitmap-add",
+        "data": {
+          "node": "n",
+          "name": "b2",
+          "persistent": true,
+          "granularity": 2097152
+       } }
+    ]
+  }
+}
+{ "execute": "quit" }
+EOF
+
+$QEMU_IMG measure -O raw -f qcow2 "$TEST_IMG"
+$QEMU_IMG measure -O qcow2 -o cluster_size=64k -f qcow2 "$TEST_IMG"
+$QEMU_IMG measure -O qcow2 -o cluster_size=2M -f qcow2 "$TEST_IMG"
+
 # success, all done
 echo "*** done"
 rm -f $seq.full
diff --git a/tests/qemu-iotests/190.out b/tests/qemu-iotests/190.out
index d001942002db..5511d53e7e7c 100644
--- a/tests/qemu-iotests/190.out
+++ b/tests/qemu-iotests/190.out
@@ -1,5 +1,5 @@
 QA output created by 190
-== Huge file ==
+== Huge file without bitmaps ==

 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=2199023255552
 required size: 2199023255552
@@ -8,4 +8,22 @@ required size: 335806464
 fully allocated size: 2199359062016
 required size: 18874368
 fully allocated size: 2199042129920
+
+== Huge file with bitmaps ==
+
+Testing: -blockdev 
driver=qcow2,node-name=n,file.driver=file,file.filename=TEST_DIR/t.qcow2
+QMP_VERSION
+{"return": {}}
+{"return": {}}
+{"return": {}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": 
"SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
+
+required size: 2199023255552
+fully allocated size: 2199023255552
+required size: 335806464
+fully allocated size: 2199359062016
+bitmaps size: 537198592
+required size: 18874368
+fully allocated size: 2199042129920
+bitmaps size: 545259520
 *** done
-- 
2.26.1