[Qemu-devel] [PATCH v3 0/4] Add shrink image for qcow2

[Qemu-devel] [PATCH v3 0/4] Add shrink image for qcow2

[Pavel Butsykin]

This patch add shrinking of the image file for qcow2. As a result, this allows
us to reduce the virtual image size and free up space on the disk without
copying the image. Image can be fragmented and shrink is done by punching holes
in the image file.

# ./qemu-img create -f qcow2 image.qcow2 4G
Formatting 'image.qcow2', fmt=qcow2 size=4294967296 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16

# ./qemu-io -c "write -P 0x22 0 1G" image.qcow2
wrote 1073741824/1073741824 bytes at offset 0
1 GiB, 1 ops; 0:00:04.59 (222.886 MiB/sec and 0.2177 ops/sec)

# ./qemu-img resize image.qcow2 512M
qemu-img: Warning: Shrinking an image will delete all data beyondthe shrunken image's end. Before performing such anoperation, make sure there is no important data there.
qemu-img: Use the --shrink option to perform a shrink operation.

# ./qemu-img resize --shrink image.qcow2 128M
Image resized.

# ./qemu-img info image.qcow2
image: image.qcow2
file format: qcow2
virtual size: 128M (134217728 bytes)
disk size: 128M
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false
    refcount bits: 16
    corrupt: false

# du -h image.qcow2 
129M    image.qcow2

Changes from v1:
- add --shrink flag for qemu-img resize
- add qcow2_cache_discard
- simplify qcow2_shrink_l1_table() to reduce the likelihood of image corruption
- add new qemu-iotests for shrinking images

Changes from v2:
- replace qprintf() on error_report() (1)
- rewrite warning messages (1)
- enforce --shrink flag for all formats except raw (1)
- split qcow2_cache_discard() (2)
- minor fixes according to comments (3)
- rewrite the last part of qcow2_shrink_reftable() to avoid
  qcow2_free_clusters() calls inside (3)
- improve test for shrinking image (4)

Pavel Butsykin (4):
  qemu-img: add --shrink flag for resize
  qcow2: add qcow2_cache_discard
  qcow2: add shrink image support
  qemu-iotests: add shrinking image test

 block/qcow2-cache.c        |  26 +++++++
 block/qcow2-cluster.c      |  40 +++++++++++
 block/qcow2-refcount.c     | 117 +++++++++++++++++++++++++++++++
 block/qcow2.c              |  42 ++++++++---
 block/qcow2.h              |  17 +++++
 qapi/block-core.json       |   3 +-
 qemu-img-cmds.hx           |   4 +-
 qemu-img.c                 |  23 ++++++
 qemu-img.texi              |   7 +-
 tests/qemu-iotests/102     |   4 +-
 tests/qemu-iotests/163     | 170 +++++++++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/163.out |   5 ++
 tests/qemu-iotests/group   |   1 +
 13 files changed, 443 insertions(+), 16 deletions(-)
 create mode 100644 tests/qemu-iotests/163
 create mode 100644 tests/qemu-iotests/163.out

-- 
2.13.0

[Qemu-devel] [PATCH v3 1/4] qemu-img: add --shrink flag for resize

[Pavel Butsykin]

The flag as additional precaution of data loss. Perhaps in the future the
operation shrink without this flag will be blocked for all formats, but while
we need to maintain compatibility with raw.

Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
---
 qemu-img-cmds.hx       |  4 ++--
 qemu-img.c             | 23 +++++++++++++++++++++++
 qemu-img.texi          |  7 ++++++-
 tests/qemu-iotests/102 |  4 ++--
 4 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/qemu-img-cmds.hx b/qemu-img-cmds.hx
index a39fcdba71..3b2eab9d20 100644
--- a/qemu-img-cmds.hx
+++ b/qemu-img-cmds.hx
@@ -76,9 +76,9 @@ STEXI
 ETEXI
 
 DEF("resize", img_resize,
-    "resize [--object objectdef] [--image-opts] [-q] filename [+ | -]size")
+    "resize [--object objectdef] [--image-opts] [-q] [--shrink] filename [+ | -]size")
 STEXI
-@item resize [--object @var{objectdef}] [--image-opts] [-q] @var{filename} [+ | -]@var{size}
+@item resize [--object @var{objectdef}] [--image-opts] [-q] [--shrink] @var{filename} [+ | -]@var{size}
 ETEXI
 
 DEF("amend", img_amend,
diff --git a/qemu-img.c b/qemu-img.c
index 91ad6bebbf..9773e835e4 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -61,6 +61,7 @@ enum {
     OPTION_FLUSH_INTERVAL = 261,
     OPTION_NO_DRAIN = 262,
     OPTION_TARGET_IMAGE_OPTS = 263,
+    OPTION_SHRINK = 264,
 };
 
 typedef enum OutputFormat {
@@ -3458,6 +3459,7 @@ static int img_resize(int argc, char **argv)
         },
     };
     bool image_opts = false;
+    bool shrink = false;
 
     /* Remove size from argv manually so that negative numbers are not treated
      * as options by getopt. */
@@ -3475,6 +3477,7 @@ static int img_resize(int argc, char **argv)
             {"help", no_argument, 0, 'h'},
             {"object", required_argument, 0, OPTION_OBJECT},
             {"image-opts", no_argument, 0, OPTION_IMAGE_OPTS},
+            {"shrink", no_argument, 0, OPTION_SHRINK},
             {0, 0, 0, 0}
         };
         c = getopt_long(argc, argv, ":f:hq",
@@ -3509,6 +3512,9 @@ static int img_resize(int argc, char **argv)
         case OPTION_IMAGE_OPTS:
             image_opts = true;
             break;
+        case OPTION_SHRINK:
+            shrink = true;
+            break;
         }
     }
     if (optind != argc - 1) {
@@ -3568,6 +3574,23 @@ static int img_resize(int argc, char **argv)
         goto out;
     }
 
+    if (total_size < blk_getlength(blk) && !shrink) {
+        error_report("Warning: Shrinking an image will delete all data beyond"
+                     "the shrunken image's end. Before performing such an"
+                     "operation, make sure there is no important data there.");
+
+        if (g_strcmp0(bdrv_get_format_name(blk_bs(blk)), "raw") != 0) {
+            error_report(
+              "Use the --shrink option to perform a shrink operation.");
+            ret = -1;
+            goto out;
+        } else {
+            error_report("Using the --shrink option will suppress this message."
+                         "Note that future versions of qemu-img may refuse to "
+                         "shrink images without this option!");
+        }
+    }
+
     ret = blk_truncate(blk, total_size, &err);
     if (!ret) {
         qprintf(quiet, "Image resized.\n");
diff --git a/qemu-img.texi b/qemu-img.texi
index 5b925ecf41..6324abef48 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -499,7 +499,7 @@ qemu-img rebase -b base.img diff.qcow2
 At this point, @code{modified.img} can be discarded, since
 @code{base.img + diff.qcow2} contains the same information.
 
-@item resize @var{filename} [+ | -]@var{size}
+@item resize [--shrink] @var{filename} [+ | -]@var{size}
 
 Change the disk image as if it had been created with @var{size}.
 
@@ -507,6 +507,11 @@ Before using this command to shrink a disk image, you MUST use file system and
 partitioning tools inside the VM to reduce allocated file systems and partition
 sizes accordingly.  Failure to do so will result in data loss!
 
+@code{--shrink} informs qemu-img that the user is certain about wanting
+to shrink an image and is aware that any data beyond the truncated
+image's end will be lost. Trying to shrink an image without this option
+results in a warning; future versions may make it an error.
+
 After using this command to grow a disk image, you must use file system and
 partitioning tools inside the VM to actually begin using the new space on the
 device.
diff --git a/tests/qemu-iotests/102 b/tests/qemu-iotests/102
index 87db1bb1bf..d7ad8d9840 100755
--- a/tests/qemu-iotests/102
+++ b/tests/qemu-iotests/102
@@ -54,7 +54,7 @@ _make_test_img $IMG_SIZE
 $QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io
 # Remove data cluster from image (first cluster: image header, second: reftable,
 # third: refblock, fourth: L1 table, fifth: L2 table)
-$QEMU_IMG resize -f raw "$TEST_IMG" $((5 * 64 * 1024))
+$QEMU_IMG resize -f raw --shrink "$TEST_IMG" $((5 * 64 * 1024))
 
 $QEMU_IO -c map "$TEST_IMG"
 $QEMU_IMG map "$TEST_IMG"
@@ -69,7 +69,7 @@ $QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io
 
 qemu_comm_method=monitor _launch_qemu -drive if=none,file="$TEST_IMG",id=drv0
 
-$QEMU_IMG resize -f raw "$TEST_IMG" $((5 * 64 * 1024))
+$QEMU_IMG resize -f raw --shrink "$TEST_IMG" $((5 * 64 * 1024))
 
 _send_qemu_cmd $QEMU_HANDLE 'qemu-io drv0 map' 'allocated' \
     | sed -e 's/^(qemu).*qemu-io drv0 map...$/(qemu) qemu-io drv0 map/'
-- 
2.13.0

[Qemu-devel] [PATCH v3 2/4] qcow2: add qcow2_cache_discard

[Pavel Butsykin]

Whenever l2/refcount table clusters are discarded from the file we can
automatically drop unnecessary content of the cache tables. This reduces
the chance of eviction useful cache data and eliminates inconsistent data
in the cache with the data in the file.

Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
---
 block/qcow2-cache.c    | 26 ++++++++++++++++++++++++++
 block/qcow2-refcount.c | 14 ++++++++++++++
 block/qcow2.h          |  3 +++
 3 files changed, 43 insertions(+)

diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index 1d25147392..75746a7f43 100644
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -411,3 +411,29 @@ void qcow2_cache_entry_mark_dirty(BlockDriverState *bs, Qcow2Cache *c,
     assert(c->entries[i].offset != 0);
     c->entries[i].dirty = true;
 }
+
+void *qcow2_cache_is_table_offset(BlockDriverState *bs, Qcow2Cache *c,
+                                  uint64_t offset)
+{
+    int i;
+
+    for (i = 0; i < c->size; i++) {
+        if (c->entries[i].offset == offset) {
+            return qcow2_cache_get_table_addr(bs, c, i);
+        }
+    }
+    return NULL;
+}
+
+void qcow2_cache_discard(BlockDriverState *bs, Qcow2Cache *c, void *table)
+{
+    int i = qcow2_cache_get_table_idx(bs, c, table);
+
+    assert(c->entries[i].ref == 0);
+
+    c->entries[i].offset = 0;
+    c->entries[i].lru_counter = 0;
+    c->entries[i].dirty = false;
+
+    qcow2_cache_table_release(bs, c, i, 1);
+}
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 7c06061aae..0141c9cbe7 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -767,6 +767,20 @@ static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
         s->set_refcount(refcount_block, block_index, refcount);
 
         if (refcount == 0 && s->discard_passthrough[type]) {
+            void *table;
+
+            table = qcow2_cache_is_table_offset(bs, s->refcount_block_cache,
+                                                offset);
+            if (table != NULL) {
+                qcow2_cache_put(bs, s->refcount_block_cache, &refcount_block);
+                qcow2_cache_discard(bs, s->refcount_block_cache, table);
+            }
+
+            table = qcow2_cache_is_table_offset(bs, s->l2_table_cache, offset);
+            if (table != NULL) {
+                qcow2_cache_discard(bs, s->l2_table_cache, table);
+            }
+
             update_refcount_discard(bs, cluster_offset, s->cluster_size);
         }
     }
diff --git a/block/qcow2.h b/block/qcow2.h
index 87b15eb4aa..bf6691dbd0 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -604,5 +604,8 @@ int qcow2_cache_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
 int qcow2_cache_get_empty(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
     void **table);
 void qcow2_cache_put(BlockDriverState *bs, Qcow2Cache *c, void **table);
+void *qcow2_cache_is_table_offset(BlockDriverState *bs, Qcow2Cache *c,
+                                  uint64_t offset);
+void qcow2_cache_discard(BlockDriverState *bs, Qcow2Cache *c, void *table);
 
 #endif
-- 
2.13.0

[Qemu-devel] [PATCH v3 3/4] qcow2: add shrink image support

[Pavel Butsykin]

This patch add shrinking of the image file for qcow2. As a result, this allows
us to reduce the virtual image size and free up space on the disk without
copying the image. Image can be fragmented and shrink is done by punching holes
in the image file.

Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
---
 block/qcow2-cluster.c  |  40 +++++++++++++++++++
 block/qcow2-refcount.c | 103 +++++++++++++++++++++++++++++++++++++++++++++++++
 block/qcow2.c          |  42 +++++++++++++++-----
 block/qcow2.h          |  14 +++++++
 qapi/block-core.json   |   3 +-
 5 files changed, 191 insertions(+), 11 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 3d341fd9cb..04d48878af 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -32,6 +32,46 @@
 #include "qemu/bswap.h"
 #include "trace.h"
 
+int qcow2_shrink_l1_table(BlockDriverState *bs, uint64_t exact_size)
+{
+    BDRVQcow2State *s = bs->opaque;
+    int new_l1_size, i, ret;
+
+    if (exact_size >= s->l1_size) {
+        return 0;
+    }
+
+    new_l1_size = exact_size;
+
+#ifdef DEBUG_ALLOC2
+    fprintf(stderr, "shrink l1_table from %d to %d\n", s->l1_size, new_l1_size);
+#endif
+
+    BLKDBG_EVENT(bs->file, BLKDBG_L1_SHRINK_WRITE_TABLE);
+    ret = bdrv_pwrite_zeroes(bs->file, s->l1_table_offset +
+                                       sizeof(uint64_t) * new_l1_size,
+                             (s->l1_size - new_l1_size) * sizeof(uint64_t), 0);
+    if (ret < 0) {
+        return ret;
+    }
+
+    ret = bdrv_flush(bs->file->bs);
+    if (ret < 0) {
+        return ret;
+    }
+
+    BLKDBG_EVENT(bs->file, BLKDBG_L1_SHRINK_FREE_L2_CLUSTERS);
+    for (i = s->l1_size - 1; i > new_l1_size - 1; i--) {
+        if ((s->l1_table[i] & L1E_OFFSET_MASK) == 0) {
+            continue;
+        }
+        qcow2_free_clusters(bs, s->l1_table[i] & L1E_OFFSET_MASK,
+                            s->cluster_size, QCOW2_DISCARD_ALWAYS);
+        s->l1_table[i] = 0;
+    }
+    return 0;
+}
+
 int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
                         bool exact_size)
 {
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 0141c9cbe7..443fca6a98 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -29,6 +29,7 @@
 #include "block/qcow2.h"
 #include "qemu/range.h"
 #include "qemu/bswap.h"
+#include "qemu/cutils.h"
 
 static int64_t alloc_clusters_noref(BlockDriverState *bs, uint64_t size);
 static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
@@ -2945,3 +2946,105 @@ done:
     qemu_vfree(new_refblock);
     return ret;
 }
+
+int qcow2_shrink_reftable(BlockDriverState *bs)
+{
+    BDRVQcow2State *s = bs->opaque;
+    uint64_t *reftable_tmp =
+        g_try_malloc(sizeof(uint64_t) * s->refcount_table_size);
+    int i, ret;
+
+    if (s->refcount_table_size && reftable_tmp == NULL) {
+        return -ENOMEM;
+    }
+
+    for (i = 0; i < s->refcount_table_size; i++) {
+        int64_t refblock_offs = s->refcount_table[i] & REFT_OFFSET_MASK;
+        void *refblock;
+        bool unused_block;
+
+        if (refblock_offs == 0) {
+            reftable_tmp[i] = 0;
+            continue;
+        }
+        ret = qcow2_cache_get(bs, s->refcount_block_cache, refblock_offs,
+                              &refblock);
+        if (ret < 0) {
+            goto out;
+        }
+
+        /* the refblock has own reference */
+        if (i == offset_to_reftable_index(s, refblock_offs)) {
+            uint64_t block_index = (refblock_offs >> s->cluster_bits) &
+                                   (s->refcount_block_size - 1);
+            uint64_t refcount = s->get_refcount(refblock, block_index);
+
+            s->set_refcount(refblock, block_index, 0);
+
+            unused_block = buffer_is_zero(refblock, s->cluster_size);
+
+            s->set_refcount(refblock, block_index, refcount);
+        } else {
+            unused_block = buffer_is_zero(refblock, s->cluster_size);
+        }
+        qcow2_cache_put(bs, s->refcount_block_cache, &refblock);
+
+        reftable_tmp[i] = unused_block ? 0 : cpu_to_be64(s->refcount_table[i]);
+    }
+
+    ret = bdrv_pwrite_sync(bs->file, s->refcount_table_offset, reftable_tmp,
+                           sizeof(uint64_t) * s->refcount_table_size);
+    if (ret < 0) {
+        goto out;
+    }
+
+    for (i = 0; i < s->refcount_table_size; i++) {
+        if (s->refcount_table[i] && !reftable_tmp[i]) {
+            uint64_t discard_offs = s->refcount_table[i] & REFT_OFFSET_MASK;
+            uint64_t refblock_offs = get_refblock_offset(s, discard_offs);
+            uint64_t cluster_index = discard_offs >> s->cluster_bits;
+            uint32_t block_index = cluster_index & (s->refcount_block_size - 1);
+            void *refblock;
+
+            assert(discard_offs != 0);
+
+            ret = qcow2_cache_get(bs, s->refcount_block_cache, refblock_offs,
+                                  &refblock);
+            if (ret < 0) {
+                goto out;
+            }
+
+            if (s->get_refcount(refblock, block_index) != 1) {
+                qcow2_cache_put(bs, s->refcount_block_cache, &refblock);
+                ret = -EINVAL;
+                goto out;
+            }
+            s->set_refcount(refblock, block_index, 0);
+
+            qcow2_cache_entry_mark_dirty(bs, s->refcount_block_cache, refblock);
+
+            qcow2_cache_put(bs, s->refcount_block_cache, &refblock);
+
+            if (cluster_index < s->free_cluster_index) {
+                s->free_cluster_index = cluster_index;
+            }
+
+            refblock = qcow2_cache_is_table_offset(bs, s->refcount_block_cache,
+                                                   discard_offs);
+            if (refblock) {
+                /* discard refblock from the cache if refblock is cached */
+                qcow2_cache_discard(bs, s->refcount_block_cache, refblock);
+            }
+            update_refcount_discard(bs, discard_offs, s->cluster_size);
+            s->refcount_table[i] = 0;
+        }
+    }
+
+    if (!s->cache_discards) {
+        qcow2_process_discards(bs, ret);
+    }
+
+out:
+    g_free(reftable_tmp);
+    return ret;
+}
diff --git a/block/qcow2.c b/block/qcow2.c
index 2f94f0326e..c7506ed971 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2589,6 +2589,7 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset, Error **errp)
 {
     BDRVQcow2State *s = bs->opaque;
     int64_t new_l1_size;
+    uint64_t total_size;
     int ret;
 
     if (offset & 511) {
@@ -2602,17 +2603,38 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset, Error **errp)
         return -ENOTSUP;
     }
 
-    /* shrinking is currently not supported */
-    if (offset < bs->total_sectors * 512) {
-        error_setg(errp, "qcow2 doesn't support shrinking images yet");
-        return -ENOTSUP;
-    }
-
     new_l1_size = size_to_l1(s, offset);
-    ret = qcow2_grow_l1_table(bs, new_l1_size, true);
-    if (ret < 0) {
-        error_setg_errno(errp, -ret, "Failed to grow the L1 table");
-        return ret;
+    total_size = bs->total_sectors << BDRV_SECTOR_BITS;
+
+    if (offset < total_size) {
+        ret = qcow2_cluster_discard(bs, ROUND_UP(offset, s->cluster_size),
+                                    total_size - ROUND_UP(offset,
+                                                          s->cluster_size),
+                                    QCOW2_DISCARD_ALWAYS, true);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to discard cropped clusters");
+            return ret;
+        }
+
+        ret = qcow2_shrink_l1_table(bs, new_l1_size);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret,
+                             "Failed to reduce the number of L2 tables");
+            return ret;
+        }
+
+        ret = qcow2_shrink_reftable(bs);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret,
+                             "Failed to discard unused refblocks");
+            return ret;
+        }
+    } else {
+        ret = qcow2_grow_l1_table(bs, new_l1_size, true);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to grow the L1 table");
+            return ret;
+        }
     }
 
     /* write updated header.size */
diff --git a/block/qcow2.h b/block/qcow2.h
index bf6691dbd0..82e83dc0d5 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -488,6 +488,18 @@ static inline uint64_t refcount_diff(uint64_t r1, uint64_t r2)
     return r1 > r2 ? r1 - r2 : r2 - r1;
 }
 
+static inline
+uint32_t offset_to_reftable_index(BDRVQcow2State *s, uint64_t offset)
+{
+    return offset >> (s->refcount_block_bits + s->cluster_bits);
+}
+
+static inline uint64_t get_refblock_offset(BDRVQcow2State *s, uint64_t offset)
+{
+    uint32_t index = offset_to_reftable_index(s, offset);
+    return s->refcount_table[index] & REFT_OFFSET_MASK;
+}
+
 /* qcow2.c functions */
 int qcow2_backing_read1(BlockDriverState *bs, QEMUIOVector *qiov,
                   int64_t sector_num, int nb_sectors);
@@ -538,10 +550,12 @@ int qcow2_pre_write_overlap_check(BlockDriverState *bs, int ign, int64_t offset,
 int qcow2_change_refcount_order(BlockDriverState *bs, int refcount_order,
                                 BlockDriverAmendStatusCB *status_cb,
                                 void *cb_opaque, Error **errp);
+int qcow2_shrink_reftable(BlockDriverState *bs);
 
 /* qcow2-cluster.c functions */
 int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
                         bool exact_size);
+int qcow2_shrink_l1_table(BlockDriverState *bs, uint64_t max_size);
 int qcow2_write_l1_entry(BlockDriverState *bs, int l1_index);
 int qcow2_decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset);
 int qcow2_encrypt_sectors(BDRVQcow2State *s, int64_t sector_num,
diff --git a/qapi/block-core.json b/qapi/block-core.json
index f85c2235c7..bcbffa3339 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -2372,7 +2372,8 @@
             'cluster_alloc_bytes', 'cluster_free', 'flush_to_os',
             'flush_to_disk', 'pwritev_rmw_head', 'pwritev_rmw_after_head',
             'pwritev_rmw_tail', 'pwritev_rmw_after_tail', 'pwritev',
-            'pwritev_zero', 'pwritev_done', 'empty_image_prepare' ] }
+            'pwritev_zero', 'pwritev_done', 'empty_image_prepare',
+            'l1_shrink_write_table', 'l1_shrink_free_l2_clusters' ] }
 
 ##
 # @BlkdebugInjectErrorOptions:
-- 
2.13.0

[Qemu-devel] [PATCH v3 4/4] qemu-iotests: add shrinking image test

[Pavel Butsykin]

Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
---
 tests/qemu-iotests/163     | 170 +++++++++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/163.out |   5 ++
 tests/qemu-iotests/group   |   1 +
 3 files changed, 176 insertions(+)
 create mode 100644 tests/qemu-iotests/163
 create mode 100644 tests/qemu-iotests/163.out

diff --git a/tests/qemu-iotests/163 b/tests/qemu-iotests/163
new file mode 100644
index 0000000000..403842354e
--- /dev/null
+++ b/tests/qemu-iotests/163
@@ -0,0 +1,170 @@
+#!/usr/bin/env python
+#
+# Tests for shrinking images
+#
+# Copyright (c) 2016-2017 Parallels International GmbH
+#
+# 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
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+import os, random, iotests, struct, qcow2
+from iotests import qemu_img, qemu_io, image_size
+
+test_img = os.path.join(iotests.test_dir, 'test.img')
+check_img = os.path.join(iotests.test_dir, 'check.img')
+
+def size_to_int(str):
+    suff = ['B', 'K', 'M', 'G', 'T']
+    return int(str[:-1]) * 1024**suff.index(str[-1:])
+
+class ShrinkBaseClass(iotests.QMPTestCase):
+    image_len = '128M'
+    shrink_size = '10M'
+    chunk_size = '16M'
+    refcount_bits = '16'
+
+    def __qcow2_check(self, filename):
+        entry_bits = 3
+        entry_size = 1 << entry_bits
+        l1_mask = 0x00fffffffffffe00
+        div_roundup = lambda n, d: (n + d - 1) / d
+
+        def split_by_n(data, n):
+            for x in xrange(0, len(data), n):
+                yield struct.unpack('>Q', data[x:x + n])[0] & l1_mask
+
+        def check_l1_table(h, l1_data):
+            l1_list = list(split_by_n(l1_data, entry_size))
+            real_l1_size = div_roundup(h.size,
+                                       1 << (h.cluster_bits*2 - entry_size))
+            used, unused = l1_list[:real_l1_size], l1_list[real_l1_size:]
+
+            self.assertTrue(len(used) != 0, "Verifying l1 table content")
+            self.assertFalse(any(unused), "Verifying l1 table content")
+
+        def check_reftable(fd, h, reftable):
+            for offset in split_by_n(reftable, entry_size):
+                if offset != 0:
+                    fd.seek(offset)
+                    cluster = fd.read(1 << h.cluster_bits)
+                    self.assertTrue(any(cluster), "Verifying reftable content")
+
+        with open(filename, "rb") as fd:
+            h = qcow2.QcowHeader(fd)
+
+            fd.seek(h.l1_table_offset)
+            l1_table = fd.read(h.l1_size << entry_bits)
+
+            fd.seek(h.refcount_table_offset)
+            reftable = fd.read(h.refcount_table_clusters << h.cluster_bits)
+
+            check_l1_table(h, l1_table)
+            check_reftable(fd, h, reftable)
+
+    def __raw_check(self, filename):
+        pass
+
+    image_check = {
+        'qcow2' : __qcow2_check,
+        'raw' : __raw_check
+    }
+
+    def setUp(self):
+        if iotests.imgfmt == 'raw':
+            qemu_img('create', '-f', iotests.imgfmt, test_img, self.image_len)
+            qemu_img('create', '-f', iotests.imgfmt, check_img,
+                     self.shrink_size)
+        else:
+            qemu_img('create', '-f', iotests.imgfmt,
+                     '-o', 'cluster_size=' + self.cluster_size +
+                     ',refcount_bits=' + self.refcount_bits,
+                     test_img, self.image_len)
+            qemu_img('create', '-f', iotests.imgfmt,
+                     '-o', 'cluster_size=%s'% self.cluster_size,
+                     check_img, self.shrink_size)
+        qemu_io('-c', 'write -P 0xff 0 ' + self.shrink_size, check_img)
+
+    def tearDown(self):
+        os.remove(test_img)
+        os.remove(check_img)
+
+    def image_verify(self):
+        self.assertEqual(image_size(test_img), image_size(check_img),
+                         "Verifying image size")
+        self.image_check[iotests.imgfmt](self, test_img)
+
+        if iotests.imgfmt == 'raw':
+            return
+        self.assertEqual(qemu_img('check', test_img), 0,
+                         "Verifying image corruption")
+
+    def test_empty_image(self):
+        qemu_img('resize',  '-f', iotests.imgfmt, '--shrink', test_img,
+                 self.shrink_size)
+
+        self.assertEqual(
+            qemu_io('-c', 'read -P 0x00 %s'%self.shrink_size, test_img),
+            qemu_io('-c', 'read -P 0x00 %s'%self.shrink_size, check_img),
+            "Verifying image content")
+
+        self.image_verify()
+
+    def test_sequential_write(self):
+        for offs in range(0, size_to_int(self.image_len),
+                          size_to_int(self.chunk_size)):
+            qemu_io('-c', 'write -P 0xff %d %s' % (offs, self.chunk_size),
+                    test_img)
+
+        qemu_img('resize',  '-f', iotests.imgfmt, '--shrink', test_img,
+                 self.shrink_size)
+
+        self.assertEqual(qemu_img("compare", test_img, check_img), 0,
+                         "Verifying image content")
+
+        self.image_verify()
+
+    def test_random_write(self):
+        offs_list = range(0, size_to_int(self.image_len),
+                          size_to_int(self.chunk_size))
+        random.shuffle(offs_list)
+        for offs in offs_list:
+            qemu_io('-c', 'write -P 0xff %d %s' % (offs, self.chunk_size),
+                    test_img)
+
+        qemu_img('resize',  '-f', iotests.imgfmt, '--shrink', test_img,
+                 self.shrink_size)
+
+        self.assertEqual(qemu_img("compare", test_img, check_img), 0,
+                         "Verifying image content")
+
+        self.image_verify()
+
+class TestShrink512(ShrinkBaseClass):
+    image_len = '3M'
+    shrink_size = '1M'
+    chunk_size = '256K'
+    cluster_size = '512'
+    refcount_bits = '64'
+
+class TestShrink64K(ShrinkBaseClass):
+    cluster_size = '64K'
+
+class TestShrink1M(ShrinkBaseClass):
+    cluster_size = '1M'
+    refcount_bits = '1'
+
+ShrinkBaseClass = None
+
+if __name__ == '__main__':
+    iotests.main(supported_fmts=['raw', 'qcow2'])
diff --git a/tests/qemu-iotests/163.out b/tests/qemu-iotests/163.out
new file mode 100644
index 0000000000..dae404e278
--- /dev/null
+++ b/tests/qemu-iotests/163.out
@@ -0,0 +1,5 @@
+.........
+----------------------------------------------------------------------
+Ran 9 tests
+
+OK
diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group
index 318ae74b10..542947eeba 100644
--- a/tests/qemu-iotests/group
+++ b/tests/qemu-iotests/group
@@ -163,6 +163,7 @@
 159 rw auto quick
 160 rw auto quick
 162 auto quick
+163 rw auto quick
 170 rw auto quick
 171 rw auto quick
 172 auto
-- 
2.13.0

Re: [Qemu-devel] [PATCH v3 1/4] qemu-img: add --shrink flag for resize

[Eric Blake]

[-- Attachment #1: Type: text/plain, Size: 4419 bytes --]

On 07/07/2017 09:30 AM, Pavel Butsykin wrote:
> The flag as additional precaution of data loss. Perhaps in the future the

s/as/is/ s/of/against/

> operation shrink without this flag will be blocked for all formats, but while

s/while/for now/

> we need to maintain compatibility with raw.
> 
> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
> ---
>  qemu-img-cmds.hx       |  4 ++--
>  qemu-img.c             | 23 +++++++++++++++++++++++
>  qemu-img.texi          |  7 ++++++-
>  tests/qemu-iotests/102 |  4 ++--
>  4 files changed, 33 insertions(+), 5 deletions(-)
> 

> @@ -3568,6 +3574,23 @@ static int img_resize(int argc, char **argv)
>          goto out;
>      }
>  
> +    if (total_size < blk_getlength(blk) && !shrink) {
> +        error_report("Warning: Shrinking an image will delete all data beyond"

Alistair has a pending thread to create a unified warning function; if
that lands first, you'll have to tweak this (if yours lands first, it's
one more place for that series to clean up).

> +                     "the shrunken image's end. Before performing such an"
> +                     "operation, make sure there is no important data there.");
> +
> +        if (g_strcmp0(bdrv_get_format_name(blk_bs(blk)), "raw") != 0) {
> +            error_report(
> +              "Use the --shrink option to perform a shrink operation.");
> +            ret = -1;
> +            goto out;
> +        } else {
> +            error_report("Using the --shrink option will suppress this message."
> +                         "Note that future versions of qemu-img may refuse to "
> +                         "shrink images without this option!");

No need to shout at the user ('.' is better than '!')

> +        }
> +    }
> +
>      ret = blk_truncate(blk, total_size, &err);
>      if (!ret) {
>          qprintf(quiet, "Image resized.\n");
> diff --git a/qemu-img.texi b/qemu-img.texi
> index 5b925ecf41..6324abef48 100644
> --- a/qemu-img.texi
> +++ b/qemu-img.texi
> @@ -499,7 +499,7 @@ qemu-img rebase -b base.img diff.qcow2
>  At this point, @code{modified.img} can be discarded, since
>  @code{base.img + diff.qcow2} contains the same information.
>  
> -@item resize @var{filename} [+ | -]@var{size}
> +@item resize [--shrink] @var{filename} [+ | -]@var{size}
>  
>  Change the disk image as if it had been created with @var{size}.
>  
> @@ -507,6 +507,11 @@ Before using this command to shrink a disk image, you MUST use file system and
>  partitioning tools inside the VM to reduce allocated file systems and partition
>  sizes accordingly.  Failure to do so will result in data loss!
>  
> +@code{--shrink} informs qemu-img that the user is certain about wanting
> +to shrink an image and is aware that any data beyond the truncated
> +image's end will be lost. Trying to shrink an image without this option
> +results in a warning; future versions may make it an error.

You made it an error for all but raw already, but I'm not sure how wordy
we want this to be.

> +
>  After using this command to grow a disk image, you must use file system and
>  partitioning tools inside the VM to actually begin using the new space on the
>  device.
> diff --git a/tests/qemu-iotests/102 b/tests/qemu-iotests/102
> index 87db1bb1bf..d7ad8d9840 100755
> --- a/tests/qemu-iotests/102
> +++ b/tests/qemu-iotests/102
> @@ -54,7 +54,7 @@ _make_test_img $IMG_SIZE
>  $QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io
>  # Remove data cluster from image (first cluster: image header, second: reftable,
>  # third: refblock, fourth: L1 table, fifth: L2 table)
> -$QEMU_IMG resize -f raw "$TEST_IMG" $((5 * 64 * 1024))
> +$QEMU_IMG resize -f raw --shrink "$TEST_IMG" $((5 * 64 * 1024))
>  
>  $QEMU_IO -c map "$TEST_IMG"
>  $QEMU_IMG map "$TEST_IMG"
> @@ -69,7 +69,7 @@ $QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io
>  
>  qemu_comm_method=monitor _launch_qemu -drive if=none,file="$TEST_IMG",id=drv0
>  
> -$QEMU_IMG resize -f raw "$TEST_IMG" $((5 * 64 * 1024))
> +$QEMU_IMG resize -f raw --shrink "$TEST_IMG" $((5 * 64 * 1024))

This tests a successful shrink. Please also test the error message when
attempting to shrink but --shrink was not supplied.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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Re: [Qemu-devel] [PATCH v3 3/4] qcow2: add shrink image support

[Eric Blake]

[-- Attachment #1: Type: text/plain, Size: 1382 bytes --]

On 07/07/2017 09:30 AM, Pavel Butsykin wrote:
> This patch add shrinking of the image file for qcow2. As a result, this allows
> us to reduce the virtual image size and free up space on the disk without
> copying the image. Image can be fragmented and shrink is done by punching holes
> in the image file.
> 
> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
> ---
>  block/qcow2-cluster.c  |  40 +++++++++++++++++++
>  block/qcow2-refcount.c | 103 +++++++++++++++++++++++++++++++++++++++++++++++++
>  block/qcow2.c          |  42 +++++++++++++++-----
>  block/qcow2.h          |  14 +++++++
>  qapi/block-core.json   |   3 +-
>  5 files changed, 191 insertions(+), 11 deletions(-)
> 

> +++ b/qapi/block-core.json
> @@ -2372,7 +2372,8 @@
>              'cluster_alloc_bytes', 'cluster_free', 'flush_to_os',
>              'flush_to_disk', 'pwritev_rmw_head', 'pwritev_rmw_after_head',
>              'pwritev_rmw_tail', 'pwritev_rmw_after_tail', 'pwritev',
> -            'pwritev_zero', 'pwritev_done', 'empty_image_prepare' ] }
> +            'pwritev_zero', 'pwritev_done', 'empty_image_prepare',
> +            'l1_shrink_write_table', 'l1_shrink_free_l2_clusters' ] }

Missing documentation for the additions.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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Re: [Qemu-devel] [PATCH v3 1/4] qemu-img: add --shrink flag for resize

[Max Reitz]

[-- Attachment #1: Type: text/plain, Size: 5278 bytes --]

On 2017-07-07 23:12, Eric Blake wrote:
> On 07/07/2017 09:30 AM, Pavel Butsykin wrote:
>> The flag as additional precaution of data loss. Perhaps in the future the
> 
> s/as/is/ s/of/against/
> 
>> operation shrink without this flag will be blocked for all formats, but while
> 
> s/while/for now/
> 
>> we need to maintain compatibility with raw.
>>
>> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
>> ---
>>  qemu-img-cmds.hx       |  4 ++--
>>  qemu-img.c             | 23 +++++++++++++++++++++++
>>  qemu-img.texi          |  7 ++++++-
>>  tests/qemu-iotests/102 |  4 ++--
>>  4 files changed, 33 insertions(+), 5 deletions(-)
>>
> 
>> @@ -3568,6 +3574,23 @@ static int img_resize(int argc, char **argv)
>>          goto out;
>>      }
>>  
>> +    if (total_size < blk_getlength(blk) && !shrink) {
>> +        error_report("Warning: Shrinking an image will delete all data beyond"
> 
> Alistair has a pending thread to create a unified warning function; if
> that lands first, you'll have to tweak this (if yours lands first, it's
> one more place for that series to clean up).
> 
>> +                     "the shrunken image's end. Before performing such an"
>> +                     "operation, make sure there is no important data there.");
>> +
>> +        if (g_strcmp0(bdrv_get_format_name(blk_bs(blk)), "raw") != 0) {
>> +            error_report(
>> +              "Use the --shrink option to perform a shrink operation.");
>> +            ret = -1;
>> +            goto out;
>> +        } else {
>> +            error_report("Using the --shrink option will suppress this message."
>> +                         "Note that future versions of qemu-img may refuse to "
>> +                         "shrink images without this option!");
> 
> No need to shout at the user ('.' is better than '!')
> 
>> +        }
>> +    }
>> +
>>      ret = blk_truncate(blk, total_size, &err);
>>      if (!ret) {
>>          qprintf(quiet, "Image resized.\n");
>> diff --git a/qemu-img.texi b/qemu-img.texi
>> index 5b925ecf41..6324abef48 100644
>> --- a/qemu-img.texi
>> +++ b/qemu-img.texi
>> @@ -499,7 +499,7 @@ qemu-img rebase -b base.img diff.qcow2
>>  At this point, @code{modified.img} can be discarded, since
>>  @code{base.img + diff.qcow2} contains the same information.
>>  
>> -@item resize @var{filename} [+ | -]@var{size}
>> +@item resize [--shrink] @var{filename} [+ | -]@var{size}
>>  
>>  Change the disk image as if it had been created with @var{size}.
>>  
>> @@ -507,6 +507,11 @@ Before using this command to shrink a disk image, you MUST use file system and
>>  partitioning tools inside the VM to reduce allocated file systems and partition
>>  sizes accordingly.  Failure to do so will result in data loss!
>>  
>> +@code{--shrink} informs qemu-img that the user is certain about wanting
>> +to shrink an image and is aware that any data beyond the truncated
>> +image's end will be lost. Trying to shrink an image without this option
>> +results in a warning; future versions may make it an error.
> 
> You made it an error for all but raw already, but I'm not sure how wordy
> we want this to be.

Easy, just make it "...image's end will be lost. This option must always
be specified when shrinking images."

(Or even just put it up front: "When shrinking images, the
@code{--shrink} option must be given.  This informs qemu-img that the
user acknowledges all loss of data beyond the truncated image's end.")

Sure, this is not entirely correct for raw images right now, but we
basically want it to be mandatory there, too.  We just cannot do it for
compatibility reasons(TM) yet -- it won't hurt to tell users the
future-proof way already.

>> +
>>  After using this command to grow a disk image, you must use file system and
>>  partitioning tools inside the VM to actually begin using the new space on the
>>  device.
>> diff --git a/tests/qemu-iotests/102 b/tests/qemu-iotests/102
>> index 87db1bb1bf..d7ad8d9840 100755
>> --- a/tests/qemu-iotests/102
>> +++ b/tests/qemu-iotests/102
>> @@ -54,7 +54,7 @@ _make_test_img $IMG_SIZE
>>  $QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io
>>  # Remove data cluster from image (first cluster: image header, second: reftable,
>>  # third: refblock, fourth: L1 table, fifth: L2 table)
>> -$QEMU_IMG resize -f raw "$TEST_IMG" $((5 * 64 * 1024))
>> +$QEMU_IMG resize -f raw --shrink "$TEST_IMG" $((5 * 64 * 1024))
>>  
>>  $QEMU_IO -c map "$TEST_IMG"
>>  $QEMU_IMG map "$TEST_IMG"
>> @@ -69,7 +69,7 @@ $QEMU_IO -c 'write 0 64k' "$TEST_IMG" | _filter_qemu_io
>>  
>>  qemu_comm_method=monitor _launch_qemu -drive if=none,file="$TEST_IMG",id=drv0
>>  
>> -$QEMU_IMG resize -f raw "$TEST_IMG" $((5 * 64 * 1024))
>> +$QEMU_IMG resize -f raw --shrink "$TEST_IMG" $((5 * 64 * 1024))
> 
> This tests a successful shrink. Please also test the error message when
> attempting to shrink but --shrink was not supplied.

This doesn't test this, it just modifies an existing test to continue to
work.  The test is added in patch 4.

With the spelling fixed as proposed by Eric, and the man page indeed
telling users to always use --shrink:

Reviewed-by: Max Reitz <mreitz@redhat.com>


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Re: [Qemu-devel] [PATCH v3 2/4] qcow2: add qcow2_cache_discard

[Max Reitz]

[-- Attachment #1: Type: text/plain, Size: 612 bytes --]

On 2017-07-07 16:30, Pavel Butsykin wrote:
> Whenever l2/refcount table clusters are discarded from the file we can
> automatically drop unnecessary content of the cache tables. This reduces
> the chance of eviction useful cache data and eliminates inconsistent data
> in the cache with the data in the file.
> 
> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
> ---
>  block/qcow2-cache.c    | 26 ++++++++++++++++++++++++++
>  block/qcow2-refcount.c | 14 ++++++++++++++
>  block/qcow2.h          |  3 +++
>  3 files changed, 43 insertions(+)

Reviewed-by: Max Reitz <mreitz@redhat.com>


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Re: [Qemu-devel] [PATCH v3 3/4] qcow2: add shrink image support

[Max Reitz]

[-- Attachment #1: Type: text/plain, Size: 1549 bytes --]

On 2017-07-07 16:30, Pavel Butsykin wrote:
> This patch add shrinking of the image file for qcow2. As a result, this allows
> us to reduce the virtual image size and free up space on the disk without
> copying the image. Image can be fragmented and shrink is done by punching holes
> in the image file.
> 
> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
> ---
>  block/qcow2-cluster.c  |  40 +++++++++++++++++++
>  block/qcow2-refcount.c | 103 +++++++++++++++++++++++++++++++++++++++++++++++++
>  block/qcow2.c          |  42 +++++++++++++++-----
>  block/qcow2.h          |  14 +++++++
>  qapi/block-core.json   |   3 +-
>  5 files changed, 191 insertions(+), 11 deletions(-)

[...]

> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> index 0141c9cbe7..443fca6a98 100644
> --- a/block/qcow2-refcount.c
> +++ b/block/qcow2-refcount.c

[...]

> @@ -2945,3 +2946,105 @@ done:

[...]

> +            ret = qcow2_cache_get(bs, s->refcount_block_cache, refblock_offs,
> +                                  &refblock);
> +            if (ret < 0) {
> +                goto out;
> +            }
> +
> +            if (s->get_refcount(refblock, block_index) != 1) {
> +                qcow2_cache_put(bs, s->refcount_block_cache, &refblock);
> +                ret = -EINVAL;

Optional: You could mark the image corrupt here.

Anyway:

Reviewed-by: Max Reitz <mreitz@redhat.com>

> +                goto out;
> +            }
> +            s->set_refcount(refblock, block_index, 0);


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Re: [Qemu-devel] [PATCH v3 3/4] qcow2: add shrink image support

[Max Reitz]

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On 2017-07-07 23:26, Eric Blake wrote:
> On 07/07/2017 09:30 AM, Pavel Butsykin wrote:
>> This patch add shrinking of the image file for qcow2. As a result, this allows
>> us to reduce the virtual image size and free up space on the disk without
>> copying the image. Image can be fragmented and shrink is done by punching holes
>> in the image file.
>>
>> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
>> ---
>>  block/qcow2-cluster.c  |  40 +++++++++++++++++++
>>  block/qcow2-refcount.c | 103 +++++++++++++++++++++++++++++++++++++++++++++++++
>>  block/qcow2.c          |  42 +++++++++++++++-----
>>  block/qcow2.h          |  14 +++++++
>>  qapi/block-core.json   |   3 +-
>>  5 files changed, 191 insertions(+), 11 deletions(-)
>>
> 
>> +++ b/qapi/block-core.json
>> @@ -2372,7 +2372,8 @@
>>              'cluster_alloc_bytes', 'cluster_free', 'flush_to_os',
>>              'flush_to_disk', 'pwritev_rmw_head', 'pwritev_rmw_after_head',
>>              'pwritev_rmw_tail', 'pwritev_rmw_after_tail', 'pwritev',
>> -            'pwritev_zero', 'pwritev_done', 'empty_image_prepare' ] }
>> +            'pwritev_zero', 'pwritev_done', 'empty_image_prepare',
>> +            'l1_shrink_write_table', 'l1_shrink_free_l2_clusters' ] }
> 
> Missing documentation for the additions.

Well, I'd say there's missing documentation for everything, so....

Max


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