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.
Reported-by: Nir Soffer <nsof...@redhat.com>
Signed-off-by: Eric Blake <ebl...@redhat.com>
---
This is independent from my 'qemu-img convert --bitmaps' series, but
highly related. As an example, if I create a 100M image, then 2
persistent bitmaps, all with default cluster/granularity sizing, I now
see:
$ ./qemu-img measure -f qcow2 -O qcow2 build/img.top
required size: 52756480
fully allocated size: 105185280
bitmaps size: 327680
which argues that I should allocate 52756480 + 327680 bytes prior to
attempting qemu-img convert --bitmaps to a pre-sized destination.
If we like the idea, I probably need to submit a 2/1 patch adding
iotest coverage of the new measurement.
qapi/block-core.json | 15 ++++++++++-----
block/qcow2.c | 25 +++++++++++++++++++++++++
qemu-img.c | 3 +++
3 files changed, 38 insertions(+), 5 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/qcow2.c b/block/qcow2.c
index b524b0c53f84..eba6c2511e60 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 +4742,26 @@ 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)) {
+ uint64_t bmsize = bdrv_dirty_bitmap_size(bm);
+ uint32_t granularity = bdrv_dirty_bitmap_granularity(bm);
+ const char *name = bdrv_dirty_bitmap_name(bm);
+ uint64_t bmclusters = DIV_ROUND_UP(bmsize / granularity
+ / 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) {
@@ -4795,6 +4818,8 @@ 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/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);
}
--
2.26.1
