[PATCH v4 0/3] qcow2: Allow resize of images with internal snapshots

[PATCH v4 0/3] qcow2: Allow resize of images with internal snapshots

[Eric Blake]

Re-posting this to make Max' life easier when rebasing on top of Kevin's work.

Based-on: <20200424125448.63318-1-kwolf@redhat.com>
[PATCH v7 00/10] block: Fix resize (extending) of short overlays

In v4:
- patch 1: fold in Max's touchups to my v3
- patch 1: resolve merge conflict on top of Kevin's block-next branch (truncate signature change)
- patch 2: resolve semantic conflict (truncate signature change)

001/3:[0004] [FC] 'block: Add blk_new_with_bs() helper'
002/3:[0002] [FC] 'qcow2: Allow resize of images with internal snapshots'
003/3:[----] [--] 'qcow2: Tweak comment about bitmaps vs. resize'

Eric Blake (3):
  block: Add blk_new_with_bs() helper
  qcow2: Allow resize of images with internal snapshots
  qcow2: Tweak comment about bitmaps vs. resize

 include/sysemu/block-backend.h |  2 ++
 block/block-backend.c          | 23 +++++++++++++++++
 block/crypto.c                 |  9 +++----
 block/parallels.c              |  8 +++---
 block/qcow.c                   |  8 +++---
 block/qcow2-snapshot.c         | 20 ++++++++++++---
 block/qcow2.c                  | 45 +++++++++++++++++++++++-----------
 block/qed.c                    |  8 +++---
 block/sheepdog.c               | 10 ++++----
 block/vdi.c                    |  8 +++---
 block/vhdx.c                   |  8 +++---
 block/vmdk.c                   |  9 +++----
 block/vpc.c                    |  8 +++---
 blockdev.c                     |  8 +++---
 blockjob.c                     |  7 ++----
 tests/qemu-iotests/061         | 35 ++++++++++++++++++++++++++
 tests/qemu-iotests/061.out     | 28 +++++++++++++++++++++
 17 files changed, 177 insertions(+), 67 deletions(-)

-- 
2.26.2

[PATCH v4 1/3] block: Add blk_new_with_bs() helper

[Eric Blake]

There are several callers that need to create a new block backend from
an existing BDS; make the task slightly easier with a common helper
routine.

Suggested-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200424190903.522087-2-eblake@redhat.com>
[mreitz: Set @ret only in error paths, see
 https://lists.nongnu.org/archive/html/qemu-block/2020-04/msg01216.html]
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 include/sysemu/block-backend.h |  2 ++
 block/block-backend.c          | 23 +++++++++++++++++++++++
 block/crypto.c                 |  9 ++++-----
 block/parallels.c              |  8 ++++----
 block/qcow.c                   |  8 ++++----
 block/qcow2.c                  | 18 ++++++++----------
 block/qed.c                    |  8 ++++----
 block/sheepdog.c               | 10 +++++-----
 block/vdi.c                    |  8 ++++----
 block/vhdx.c                   |  8 ++++----
 block/vmdk.c                   |  9 ++++-----
 block/vpc.c                    |  8 ++++----
 blockdev.c                     |  8 +++-----
 blockjob.c                     |  7 ++-----
 14 files changed, 75 insertions(+), 59 deletions(-)

diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index 34de7faa81de..0917663d89f4 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -77,6 +77,8 @@ typedef struct BlockBackendPublic {
 } BlockBackendPublic;

 BlockBackend *blk_new(AioContext *ctx, uint64_t perm, uint64_t shared_perm);
+BlockBackend *blk_new_with_bs(BlockDriverState *bs, uint64_t perm,
+                              uint64_t shared_perm, Error **errp);
 BlockBackend *blk_new_open(const char *filename, const char *reference,
                            QDict *options, int flags, Error **errp);
 int blk_get_refcnt(BlockBackend *blk);
diff --git a/block/block-backend.c b/block/block-backend.c
index 17ed6d8c5b27..f4944861fa4e 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -355,6 +355,29 @@ BlockBackend *blk_new(AioContext *ctx, uint64_t perm, uint64_t shared_perm)
     return blk;
 }

+/*
+ * Create a new BlockBackend connected to an existing BlockDriverState.
+ *
+ * @perm is a bitmasks of BLK_PERM_* constants which describes the
+ * permissions to request for @bs that is attached to this
+ * BlockBackend.  @shared_perm is a bitmask which describes which
+ * permissions may be granted to other users of the attached node.
+ * Both sets of permissions can be changed later using blk_set_perm().
+ *
+ * Return the new BlockBackend on success, null on failure.
+ */
+BlockBackend *blk_new_with_bs(BlockDriverState *bs, uint64_t perm,
+                              uint64_t shared_perm, Error **errp)
+{
+    BlockBackend *blk = blk_new(bdrv_get_aio_context(bs), perm, shared_perm);
+
+    if (blk_insert_bs(blk, bs, errp) < 0) {
+        blk_unref(blk);
+        return NULL;
+    }
+    return blk;
+}
+
 /*
  * Creates a new BlockBackend, opens a new BlockDriverState, and connects both.
  * The new BlockBackend is in the main AioContext.
diff --git a/block/crypto.c b/block/crypto.c
index e02f34359019..ca44dae4f7e8 100644
--- a/block/crypto.c
+++ b/block/crypto.c
@@ -261,11 +261,10 @@ static int block_crypto_co_create_generic(BlockDriverState *bs,
     QCryptoBlock *crypto = NULL;
     struct BlockCryptoCreateData data;

-    blk = blk_new(bdrv_get_aio_context(bs),
-                  BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
-
-    ret = blk_insert_bs(blk, bs, errp);
-    if (ret < 0) {
+    blk = blk_new_with_bs(bs, BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL,
+                          errp);
+    if (!blk) {
+        ret = -EPERM;
         goto cleanup;
     }

diff --git a/block/parallels.c b/block/parallels.c
index 2be92cf41708..8db64a55e3ae 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -559,10 +559,10 @@ static int coroutine_fn parallels_co_create(BlockdevCreateOptions* opts,
         return -EIO;
     }

-    blk = blk_new(bdrv_get_aio_context(bs),
-                  BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
-    ret = blk_insert_bs(blk, bs, errp);
-    if (ret < 0) {
+    blk = blk_new_with_bs(bs, BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL,
+                          errp);
+    if (!blk) {
+        ret = -EPERM;
         goto out;
     }
     blk_set_allow_write_beyond_eof(blk, true);
diff --git a/block/qcow.c b/block/qcow.c
index 6b5f2269f0ba..b0475b73a551 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -849,10 +849,10 @@ static int coroutine_fn qcow_co_create(BlockdevCreateOptions *opts,
         return -EIO;
     }

-    qcow_blk = blk_new(bdrv_get_aio_context(bs),
-                       BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
-    ret = blk_insert_bs(qcow_blk, bs, errp);
-    if (ret < 0) {
+    qcow_blk = blk_new_with_bs(bs, BLK_PERM_WRITE | BLK_PERM_RESIZE,
+                               BLK_PERM_ALL, errp);
+    if (!qcow_blk) {
+        ret = -EPERM;
         goto exit;
     }
     blk_set_allow_write_beyond_eof(qcow_blk, true);
diff --git a/block/qcow2.c b/block/qcow2.c
index 2ba0b17c391c..0edc7f4643f8 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -3405,10 +3405,10 @@ qcow2_co_create(BlockdevCreateOptions *create_options, Error **errp)
     }

     /* Create BlockBackend to write to the image */
-    blk = blk_new(bdrv_get_aio_context(bs),
-                  BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
-    ret = blk_insert_bs(blk, bs, errp);
-    if (ret < 0) {
+    blk = blk_new_with_bs(bs, BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL,
+                          errp);
+    if (!blk) {
+        ret = -EPERM;
         goto out;
     }
     blk_set_allow_write_beyond_eof(blk, true);
@@ -5412,12 +5412,10 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
     }

     if (new_size) {
-        BlockBackend *blk = blk_new(bdrv_get_aio_context(bs),
-                                    BLK_PERM_RESIZE, BLK_PERM_ALL);
-        ret = blk_insert_bs(blk, bs, errp);
-        if (ret < 0) {
-            blk_unref(blk);
-            return ret;
+        BlockBackend *blk = blk_new_with_bs(bs, BLK_PERM_RESIZE, BLK_PERM_ALL,
+                                            errp);
+        if (!blk) {
+            return -EPERM;
         }

         /*
diff --git a/block/qed.c b/block/qed.c
index b0fdb8f56508..fb609cfba17a 100644
--- a/block/qed.c
+++ b/block/qed.c
@@ -651,10 +651,10 @@ static int coroutine_fn bdrv_qed_co_create(BlockdevCreateOptions *opts,
         return -EIO;
     }

-    blk = blk_new(bdrv_get_aio_context(bs),
-                  BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
-    ret = blk_insert_bs(blk, bs, errp);
-    if (ret < 0) {
+    blk = blk_new_with_bs(bs, BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL,
+                          errp);
+    if (!blk) {
+        ret = -EPERM;
         goto out;
     }
     blk_set_allow_write_beyond_eof(blk, true);
diff --git a/block/sheepdog.c b/block/sheepdog.c
index ef0a6e743e27..39010c3f55bb 100644
--- a/block/sheepdog.c
+++ b/block/sheepdog.c
@@ -1803,12 +1803,12 @@ static int sd_prealloc(BlockDriverState *bs, int64_t old_size, int64_t new_size,
     void *buf = NULL;
     int ret;

-    blk = blk_new(bdrv_get_aio_context(bs),
-                  BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE | BLK_PERM_RESIZE,
-                  BLK_PERM_ALL);
+    blk = blk_new_with_bs(bs,
+                          BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE | BLK_PERM_RESIZE,
+                          BLK_PERM_ALL, errp);

-    ret = blk_insert_bs(blk, bs, errp);
-    if (ret < 0) {
+    if (!blk) {
+        ret = -EPERM;
         goto out_with_err_set;
     }

diff --git a/block/vdi.c b/block/vdi.c
index 0c7835ae70a0..2d2804661527 100644
--- a/block/vdi.c
+++ b/block/vdi.c
@@ -804,10 +804,10 @@ static int coroutine_fn vdi_co_do_create(BlockdevCreateOptions *create_options,
         goto exit;
     }

-    blk = blk_new(bdrv_get_aio_context(bs_file),
-                  BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
-    ret = blk_insert_bs(blk, bs_file, errp);
-    if (ret < 0) {
+    blk = blk_new_with_bs(bs_file, BLK_PERM_WRITE | BLK_PERM_RESIZE,
+                          BLK_PERM_ALL, errp);
+    if (!blk) {
+        ret = -EPERM;
         goto exit;
     }

diff --git a/block/vhdx.c b/block/vhdx.c
index 21497f731878..9416cd3fd572 100644
--- a/block/vhdx.c
+++ b/block/vhdx.c
@@ -1984,10 +1984,10 @@ static int coroutine_fn vhdx_co_create(BlockdevCreateOptions *opts,
         return -EIO;
     }

-    blk = blk_new(bdrv_get_aio_context(bs),
-                  BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
-    ret = blk_insert_bs(blk, bs, errp);
-    if (ret < 0) {
+    blk = blk_new_with_bs(bs, BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL,
+                          errp);
+    if (!blk) {
+        ret = -EPERM;
         goto delete_and_exit;
     }
     blk_set_allow_write_beyond_eof(blk, true);
diff --git a/block/vmdk.c b/block/vmdk.c
index 8ec18f35a536..b02fdd14b2d0 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -2717,11 +2717,10 @@ static BlockBackend *vmdk_co_create_cb(int64_t size, int idx,
     if (!bs) {
         return NULL;
     }
-    blk = blk_new(bdrv_get_aio_context(bs),
-                  BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE | BLK_PERM_RESIZE,
-                  BLK_PERM_ALL);
-    if (blk_insert_bs(blk, bs, errp)) {
-        bdrv_unref(bs);
+    blk = blk_new_with_bs(bs,
+                          BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE | BLK_PERM_RESIZE,
+                          BLK_PERM_ALL, errp);
+    if (!blk) {
         return NULL;
     }
     blk_set_allow_write_beyond_eof(blk, true);
diff --git a/block/vpc.c b/block/vpc.c
index 2d1eade146b7..5e31dd1e47a1 100644
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -1012,10 +1012,10 @@ static int coroutine_fn vpc_co_create(BlockdevCreateOptions *opts,
         return -EIO;
     }

-    blk = blk_new(bdrv_get_aio_context(bs),
-                  BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
-    ret = blk_insert_bs(blk, bs, errp);
-    if (ret < 0) {
+    blk = blk_new_with_bs(bs, BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL,
+                          errp);
+    if (!blk) {
+        ret = -EPERM;
         goto out;
     }
     blk_set_allow_write_beyond_eof(blk, true);
diff --git a/blockdev.c b/blockdev.c
index fbe3a06dbf93..e5b018320ab1 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2711,7 +2711,6 @@ void qmp_block_resize(bool has_device, const char *device,
     BlockBackend *blk = NULL;
     BlockDriverState *bs;
     AioContext *aio_context;
-    int ret;

     bs = bdrv_lookup_bs(has_device ? device : NULL,
                         has_node_name ? node_name : NULL,
@@ -2734,14 +2733,13 @@ void qmp_block_resize(bool has_device, const char *device,
         goto out;
     }

-    blk = blk_new(bdrv_get_aio_context(bs), BLK_PERM_RESIZE, BLK_PERM_ALL);
-    ret = blk_insert_bs(blk, bs, errp);
-    if (ret < 0) {
+    blk = blk_new_with_bs(bs, BLK_PERM_RESIZE, BLK_PERM_ALL, errp);
+    if (!blk) {
         goto out;
     }

     bdrv_drained_begin(bs);
-    ret = blk_truncate(blk, size, false, PREALLOC_MODE_OFF, 0, errp);
+    blk_truncate(blk, size, false, PREALLOC_MODE_OFF, 0, errp);
     bdrv_drained_end(bs);

 out:
diff --git a/blockjob.c b/blockjob.c
index fc850312c124..2affa1844d4f 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -397,16 +397,13 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
 {
     BlockBackend *blk;
     BlockJob *job;
-    int ret;

     if (job_id == NULL && !(flags & JOB_INTERNAL)) {
         job_id = bdrv_get_device_name(bs);
     }

-    blk = blk_new(bdrv_get_aio_context(bs), perm, shared_perm);
-    ret = blk_insert_bs(blk, bs, errp);
-    if (ret < 0) {
-        blk_unref(blk);
+    blk = blk_new_with_bs(bs, perm, shared_perm, errp);
+    if (!blk) {
         return NULL;
     }

-- 
2.26.2

[PATCH v4 2/3] qcow2: Allow resize of images with internal snapshots

[Eric Blake]

We originally refused to allow resize of images with internal
snapshots because the v2 image format did not require the tracking of
snapshot size, making it impossible to safely revert to a snapshot
with a different size than the current view of the image.  But the
snapshot size tracking was rectified in v3, and our recent fixes to
qemu-img amend (see 0a85af35) guarantee that we always have a valid
snapshot size.  Thus, we no longer need to artificially limit image
resizes, but it does become one more thing that would prevent a
downgrade back to v2.  And now that we support different-sized
snapshots, it's also easy to fix reverting to a snapshot to apply the
new size.

Upgrade iotest 61 to cover this (we previously had NO coverage of
refusal to resize while snapshots exist).  Note that the amend process
can fail but still have effects: in particular, since we break things
into upgrade, resize, downgrade, a failure during resize does not roll
back changes made during upgrade, nor does failure in downgrade roll
back a resize.  But this situation is pre-existing even without this
patch; and without journaling, the best we could do is minimize the
chance of partial failure by collecting all changes prior to doing any
writes - which adds a lot of complexity but could still fail with EIO.
On the other hand, we are careful that even if we have partial
modification but then fail, the image is left viable (that is, we are
careful to sequence things so that after each successful cluster
write, there may be transient leaked clusters but no corrupt
metadata).  And complicating the code to make it more transaction-like
is not worth the effort: a user can always request multiple 'qemu-img
amend' changing one thing each, if they need finer-grained control
over detecting the first failure than what they get by letting qemu
decide how to sequence multiple changes.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2-snapshot.c     | 20 ++++++++++++++++----
 block/qcow2.c              | 25 ++++++++++++++++++++++---
 tests/qemu-iotests/061     | 35 +++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/061.out | 28 ++++++++++++++++++++++++++++
 4 files changed, 101 insertions(+), 7 deletions(-)

diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 82c32d4c9b08..2756b37d2427 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -23,6 +23,7 @@
  */

 #include "qemu/osdep.h"
+#include "sysemu/block-backend.h"
 #include "qapi/error.h"
 #include "qcow2.h"
 #include "qemu/bswap.h"
@@ -775,10 +776,21 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
     }

     if (sn->disk_size != bs->total_sectors * BDRV_SECTOR_SIZE) {
-        error_report("qcow2: Loading snapshots with different disk "
-            "size is not implemented");
-        ret = -ENOTSUP;
-        goto fail;
+        BlockBackend *blk = blk_new_with_bs(bs, BLK_PERM_RESIZE, BLK_PERM_ALL,
+                                            &local_err);
+        if (!blk) {
+            error_report_err(local_err);
+            ret = -ENOTSUP;
+            goto fail;
+        }
+
+        ret = blk_truncate(blk, sn->disk_size, true, PREALLOC_MODE_OFF, 0,
+                           &local_err);
+        blk_unref(blk);
+        if (ret < 0) {
+            error_report_err(local_err);
+            goto fail;
+        }
     }

     /*
diff --git a/block/qcow2.c b/block/qcow2.c
index 0edc7f4643f8..3e8b3d022b80 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -3989,9 +3989,12 @@ static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset,

     qemu_co_mutex_lock(&s->lock);

-    /* cannot proceed if image has snapshots */
-    if (s->nb_snapshots) {
-        error_setg(errp, "Can't resize an image which has snapshots");
+    /*
+     * Even though we store snapshot size for all images, it was not
+     * required until v3, so it is not safe to proceed for v2.
+     */
+    if (s->nb_snapshots && s->qcow_version < 3) {
+        error_setg(errp, "Can't resize a v2 image which has snapshots");
         ret = -ENOTSUP;
         goto fail;
     }
@@ -5005,6 +5008,7 @@ static int qcow2_downgrade(BlockDriverState *bs, int target_version,
     BDRVQcow2State *s = bs->opaque;
     int current_version = s->qcow_version;
     int ret;
+    int i;

     /* This is qcow2_downgrade(), not qcow2_upgrade() */
     assert(target_version < current_version);
@@ -5022,6 +5026,21 @@ static int qcow2_downgrade(BlockDriverState *bs, int target_version,
         return -ENOTSUP;
     }

+    /*
+     * If any internal snapshot has a different size than the current
+     * image size, or VM state size that exceeds 32 bits, downgrading
+     * is unsafe.  Even though we would still use v3-compliant output
+     * to preserve that data, other v2 programs might not realize
+     * those optional fields are important.
+     */
+    for (i = 0; i < s->nb_snapshots; i++) {
+        if (s->snapshots[i].vm_state_size > UINT32_MAX ||
+            s->snapshots[i].disk_size != bs->total_sectors * BDRV_SECTOR_SIZE) {
+            error_setg(errp, "Internal snapshots prevent downgrade of image");
+            return -ENOTSUP;
+        }
+    }
+
     /* clear incompatible features */
     if (s->incompatible_features & QCOW2_INCOMPAT_DIRTY) {
         ret = qcow2_mark_clean(bs);
diff --git a/tests/qemu-iotests/061 b/tests/qemu-iotests/061
index ce285d308408..10eb24316461 100755
--- a/tests/qemu-iotests/061
+++ b/tests/qemu-iotests/061
@@ -111,6 +111,41 @@ $PYTHON qcow2.py "$TEST_IMG" dump-header
 $QEMU_IO -c "read -P 0x2a 42M 64k" "$TEST_IMG" | _filter_qemu_io
 _check_test_img

+echo
+echo "=== Testing resize with snapshots ==="
+echo
+_make_test_img -o "compat=0.10" 32M
+$QEMU_IO -c "write -P 0x2a 24M 64k" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IMG snapshot -c foo "$TEST_IMG"
+$QEMU_IMG resize "$TEST_IMG" 64M &&
+    echo "unexpected pass"
+$PYTHON qcow2.py "$TEST_IMG" dump-header | grep '^\(version\|size\|nb_snap\)'
+
+$QEMU_IMG amend -o "compat=1.1,size=128M" "$TEST_IMG" ||
+    echo "unexpected fail"
+$PYTHON qcow2.py "$TEST_IMG" dump-header | grep '^\(version\|size\|nb_snap\)'
+
+$QEMU_IMG snapshot -c bar "$TEST_IMG"
+$QEMU_IMG resize --shrink "$TEST_IMG" 64M ||
+    echo "unexpected fail"
+$PYTHON qcow2.py "$TEST_IMG" dump-header | grep '^\(version\|size\|nb_snap\)'
+
+$QEMU_IMG amend -o "compat=0.10,size=32M" "$TEST_IMG" &&
+    echo "unexpected pass"
+$PYTHON qcow2.py "$TEST_IMG" dump-header | grep '^\(version\|size\|nb_snap\)'
+
+$QEMU_IMG snapshot -a bar "$TEST_IMG" ||
+    echo "unexpected fail"
+$PYTHON qcow2.py "$TEST_IMG" dump-header | grep '^\(version\|size\|nb_snap\)'
+
+$QEMU_IMG snapshot -d bar "$TEST_IMG"
+$QEMU_IMG amend -o "compat=0.10,size=32M" "$TEST_IMG" ||
+    echo "unexpected fail"
+$PYTHON qcow2.py "$TEST_IMG" dump-header | grep '^\(version\|size\|nb_snap\)'
+
+_check_test_img
+
+
 echo
 echo "=== Testing dirty lazy_refcounts=off ==="
 echo
diff --git a/tests/qemu-iotests/061.out b/tests/qemu-iotests/061.out
index 413cc4e0f4ab..5a8d36d0058a 100644
--- a/tests/qemu-iotests/061.out
+++ b/tests/qemu-iotests/061.out
@@ -271,6 +271,34 @@ read 65536/65536 bytes at offset 44040192
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 No errors were found on the image.

+=== Testing resize with snapshots ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=33554432
+wrote 65536/65536 bytes at offset 25165824
+64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+qemu-img: Can't resize a v2 image which has snapshots
+version                   2
+size                      33554432
+nb_snapshots              1
+version                   3
+size                      134217728
+nb_snapshots              1
+Image resized.
+version                   3
+size                      67108864
+nb_snapshots              2
+qemu-img: Internal snapshots prevent downgrade of image
+version                   3
+size                      33554432
+nb_snapshots              2
+version                   3
+size                      134217728
+nb_snapshots              2
+version                   2
+size                      33554432
+nb_snapshots              1
+No errors were found on the image.
+
 === Testing dirty lazy_refcounts=off ===

 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864
-- 
2.26.2

[PATCH v4 3/3] qcow2: Tweak comment about bitmaps vs. resize

[Eric Blake]

Our comment did not actually match the code.  Rewrite the comment to
be less sensitive to any future changes to qcow2-bitmap.c that might
implement scenarios that we currently reject.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 3e8b3d022b80..ad934109a813 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -3999,7 +3999,7 @@ static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
         goto fail;
     }

-    /* cannot proceed if image has bitmaps */
+    /* See qcow2-bitmap.c for which bitmap scenarios prevent a resize. */
     if (qcow2_truncate_bitmaps_check(bs, errp)) {
         ret = -ENOTSUP;
         goto fail;
-- 
2.26.2

Re: [PATCH v4 0/3] qcow2: Allow resize of images with internal snapshots

[Max Reitz]

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On 28.04.20 21:26, Eric Blake wrote:
> Re-posting this to make Max' life easier when rebasing on top of Kevin's work.
> 
> Based-on: <20200424125448.63318-1-kwolf@redhat.com>
> [PATCH v7 00/10] block: Fix resize (extending) of short overlays
> 
> In v4:
> - patch 1: fold in Max's touchups to my v3
> - patch 1: resolve merge conflict on top of Kevin's block-next branch (truncate signature change)
> - patch 2: resolve semantic conflict (truncate signature change)
> 
> 001/3:[0004] [FC] 'block: Add blk_new_with_bs() helper'
> 002/3:[0002] [FC] 'qcow2: Allow resize of images with internal snapshots'
> 003/3:[----] [--] 'qcow2: Tweak comment about bitmaps vs. resize'

Thanks, I’ve updated my branch:

https://git.xanclic.moe/XanClic/qemu/commits/branch/block-next

(A commit with two Message-Id tags is interesting :))

Max


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