[PATCH v3 0/5] fix & merge block_status_above and is_allocated_above

[PATCH v3 0/5] fix & merge block_status_above and is_allocated_above

[Vladimir Sementsov-Ogievskiy]

Hi all!

v3: fix regression in 01 [Eric]

These series are here to address the following problem:
block-status-above functions may consider space after EOF of
intermediate backing files as unallocated, which is wrong, as these
backing files are the reason of producing zeroes, we never go further by
backing chain after a short backing file. So, if such short-backing file
is _inside_ requested sub-chain of the backing chain, we should never
report space after its EOF as unallocated.

See patches 01,04,05 for details.

Note, that this series leaves for another day the general problem
around block-status: misuse of BDRV_BLOCK_ALLOCATED as is-fs-allocated
vs go-to-backing.
Audit for this problem is done here:
"backing chain & block status & filters"
https://lists.gnu.org/archive/html/qemu-devel/2020-04/msg04706.html
And I'm going to prepare series to address this problem.

Also, get_block_status func have same disease, but remains unfixed here:
I want to make separate series for it, as it need some more refactoring,
which should be based on patch
"[PATCH v2] block: Factor out bdrv_run_co()"

Vladimir Sementsov-Ogievskiy (5):
  block/io: fix bdrv_co_block_status_above
  block/io: bdrv_common_block_status_above: support include_base
  block/io: bdrv_common_block_status_above: support bs == base
  block/io: fix bdrv_is_allocated_above
  iotests: add commit top->base cases to 274

 block/io.c                 | 105 +++++++++++++++++++------------------
 block/qcow2.c              |  16 +++++-
 tests/qemu-iotests/274     |  20 +++++++
 tests/qemu-iotests/274.out |  65 +++++++++++++++++++++++
 4 files changed, 152 insertions(+), 54 deletions(-)

-- 
2.21.0

[PATCH v3 1/5] block/io: fix bdrv_co_block_status_above

[Vladimir Sementsov-Ogievskiy]

bdrv_co_block_status_above has several design problems with handling
short backing files:

1. With want_zeros=true, it may return ret with BDRV_BLOCK_ZERO but
without BDRV_BLOCK_ALLOCATED flag, when actually short backing file
which produces these after-EOF zeros is inside requested backing
sequence.

2. With want_zero=false, it may return pnum=0 prior to actual EOF,
because of EOF of short backing file.

Fix these things, making logic about short backing files clearer.

With fixed bdrv_block_status_above we also have to improve is_zero in
qcow2 code, otherwise iotest 154 will fail, because with this patch we
stop to merge zeros of different types (produced by fully unallocated
in the whole backing chain regions vs produced by short backing files).

Note also, that this patch leaves for another day the general problem
around block-status: misuse of BDRV_BLOCK_ALLOCATED as is-fs-allocated
vs go-to-backing.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/io.c    | 39 ++++++++++++++++++++++++++++++---------
 block/qcow2.c | 16 ++++++++++++++--
 2 files changed, 44 insertions(+), 11 deletions(-)

diff --git a/block/io.c b/block/io.c
index 121ce17a49..412b91b08f 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2461,25 +2461,46 @@ static int coroutine_fn bdrv_co_block_status_above(BlockDriverState *bs,
         ret = bdrv_co_block_status(p, want_zero, offset, bytes, pnum, map,
                                    file);
         if (ret < 0) {
-            break;
+            return ret;
         }
-        if (ret & BDRV_BLOCK_ZERO && ret & BDRV_BLOCK_EOF && !first) {
+        if (*pnum == 0) {
+            if (first) {
+                return ret;
+            }
+
             /*
-             * Reading beyond the end of the file continues to read
-             * zeroes, but we can only widen the result to the
-             * unallocated length we learned from an earlier
-             * iteration.
+             * The top layer deferred to this layer, and because this layer is
+             * short, any zeroes that we synthesize beyond EOF behave as if they
+             * were allocated at this layer
              */
+            assert(ret & BDRV_BLOCK_EOF);
             *pnum = bytes;
+            if (file) {
+                *file = p;
+            }
+            return BDRV_BLOCK_ZERO | BDRV_BLOCK_ALLOCATED;
         }
-        if (ret & (BDRV_BLOCK_ZERO | BDRV_BLOCK_DATA)) {
-            break;
+        if (ret & BDRV_BLOCK_ALLOCATED) {
+            /* We've found the node and the status, we must return. */
+
+            if (ret & BDRV_BLOCK_ZERO && ret & BDRV_BLOCK_EOF && !first) {
+                /*
+                 * This level is also responsible for reads after EOF inside
+                 * the unallocated region in the previous level.
+                 */
+                *pnum = bytes;
+            }
+
+            return ret;
         }
+
         /* [offset, pnum] unallocated on this layer, which could be only
          * the first part of [offset, bytes].  */
-        bytes = MIN(bytes, *pnum);
+        assert(*pnum <= bytes);
+        bytes = *pnum;
         first = false;
     }
+
     return ret;
 }
 
diff --git a/block/qcow2.c b/block/qcow2.c
index fe0ce39799..ac43c58c7e 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -3827,8 +3827,20 @@ static bool is_zero(BlockDriverState *bs, int64_t offset, int64_t bytes)
     if (!bytes) {
         return true;
     }
-    res = bdrv_block_status_above(bs, NULL, offset, bytes, &nr, NULL, NULL);
-    return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == bytes;
+
+    /*
+     * bdrv_block_status_above doesn't merge different types of zeros, for
+     * example, zeros which comes from the region which is unallocated in
+     * the whole backing chain, and zeros which comes because of short backing
+     * file. So, we need a loop.
+     */
+    do {
+        res = bdrv_block_status_above(bs, NULL, offset, bytes, &nr, NULL, NULL);
+        offset += nr;
+        bytes -= nr;
+    } while (res >= 0 && (res & BDRV_BLOCK_ZERO) && nr && bytes);
+
+    return res >= 0 && (res & BDRV_BLOCK_ZERO) && bytes == 0;
 }
 
 static coroutine_fn int qcow2_co_pwrite_zeroes(BlockDriverState *bs,
-- 
2.21.0

[PATCH v3 2/5] block/io: bdrv_common_block_status_above: support include_base

[Vladimir Sementsov-Ogievskiy]

In order to reuse bdrv_common_block_status_above in
bdrv_is_allocated_above, let's support include_base parameter.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
---
 block/io.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/block/io.c b/block/io.c
index 412b91b08f..ae1c806720 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2223,6 +2223,7 @@ int bdrv_flush_all(void)
 typedef struct BdrvCoBlockStatusData {
     BlockDriverState *bs;
     BlockDriverState *base;
+    bool include_base;
     bool want_zero;
     int64_t offset;
     int64_t bytes;
@@ -2445,6 +2446,7 @@ early_out:
 
 static int coroutine_fn bdrv_co_block_status_above(BlockDriverState *bs,
                                                    BlockDriverState *base,
+                                                   bool include_base,
                                                    bool want_zero,
                                                    int64_t offset,
                                                    int64_t bytes,
@@ -2456,8 +2458,8 @@ static int coroutine_fn bdrv_co_block_status_above(BlockDriverState *bs,
     int ret = 0;
     bool first = true;
 
-    assert(bs != base);
-    for (p = bs; p != base; p = backing_bs(p)) {
+    assert(include_base || bs != base);
+    for (p = bs; include_base || p != base; p = backing_bs(p)) {
         ret = bdrv_co_block_status(p, want_zero, offset, bytes, pnum, map,
                                    file);
         if (ret < 0) {
@@ -2496,6 +2498,11 @@ static int coroutine_fn bdrv_co_block_status_above(BlockDriverState *bs,
 
         /* [offset, pnum] unallocated on this layer, which could be only
          * the first part of [offset, bytes].  */
+
+        if (p == base) {
+            break;
+        }
+
         assert(*pnum <= bytes);
         bytes = *pnum;
         first = false;
@@ -2510,7 +2517,7 @@ static void coroutine_fn bdrv_block_status_above_co_entry(void *opaque)
     BdrvCoBlockStatusData *data = opaque;
 
     data->ret = bdrv_co_block_status_above(data->bs, data->base,
-                                           data->want_zero,
+                                           data->include_base, data->want_zero,
                                            data->offset, data->bytes,
                                            data->pnum, data->map, data->file);
     data->done = true;
@@ -2524,6 +2531,7 @@ static void coroutine_fn bdrv_block_status_above_co_entry(void *opaque)
  */
 static int bdrv_common_block_status_above(BlockDriverState *bs,
                                           BlockDriverState *base,
+                                          bool include_base,
                                           bool want_zero, int64_t offset,
                                           int64_t bytes, int64_t *pnum,
                                           int64_t *map,
@@ -2533,6 +2541,7 @@ static int bdrv_common_block_status_above(BlockDriverState *bs,
     BdrvCoBlockStatusData data = {
         .bs = bs,
         .base = base,
+        .include_base = include_base,
         .want_zero = want_zero,
         .offset = offset,
         .bytes = bytes,
@@ -2557,7 +2566,7 @@ int bdrv_block_status_above(BlockDriverState *bs, BlockDriverState *base,
                             int64_t offset, int64_t bytes, int64_t *pnum,
                             int64_t *map, BlockDriverState **file)
 {
-    return bdrv_common_block_status_above(bs, base, true, offset, bytes,
+    return bdrv_common_block_status_above(bs, base, false, true, offset, bytes,
                                           pnum, map, file);
 }
 
@@ -2574,7 +2583,7 @@ int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
     int ret;
     int64_t dummy;
 
-    ret = bdrv_common_block_status_above(bs, backing_bs(bs), false, offset,
+    ret = bdrv_common_block_status_above(bs, bs, true, false, offset,
                                          bytes, pnum ? pnum : &dummy, NULL,
                                          NULL);
     if (ret < 0) {
-- 
2.21.0

[PATCH v3 3/5] block/io: bdrv_common_block_status_above: support bs == base

[Vladimir Sementsov-Ogievskiy]

We are going to reuse bdrv_common_block_status_above in
bdrv_is_allocated_above. bdrv_is_allocated_above may be called with
include_base == false and still bs == base (for ex. from img_rebase()).

So, support this corner case.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
---
 block/io.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/block/io.c b/block/io.c
index ae1c806720..6f90b322f4 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2458,7 +2458,11 @@ static int coroutine_fn bdrv_co_block_status_above(BlockDriverState *bs,
     int ret = 0;
     bool first = true;
 
-    assert(include_base || bs != base);
+    if (!include_base && bs == base) {
+        *pnum = bytes;
+        return 0;
+    }
+
     for (p = bs; include_base || p != base; p = backing_bs(p)) {
         ret = bdrv_co_block_status(p, want_zero, offset, bytes, pnum, map,
                                    file);
-- 
2.21.0

[PATCH v3 4/5] block/io: fix bdrv_is_allocated_above

[Vladimir Sementsov-Ogievskiy]

bdrv_is_allocated_above wrongly handles short backing files: it reports
after-EOF space as UNALLOCATED which is wrong, as on read the data is
generated on the level of short backing file (if all overlays has
unallocated area at that place).

Reusing bdrv_common_block_status_above fixes the issue and unifies code
path.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/io.c | 43 +++++--------------------------------------
 1 file changed, 5 insertions(+), 38 deletions(-)

diff --git a/block/io.c b/block/io.c
index 6f90b322f4..e952f3d9a5 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2611,52 +2611,19 @@ int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
  * at 'offset + *pnum' may return the same allocation status (in other
  * words, the result is not necessarily the maximum possible range);
  * but 'pnum' will only be 0 when end of file is reached.
- *
  */
 int bdrv_is_allocated_above(BlockDriverState *top,
                             BlockDriverState *base,
                             bool include_base, int64_t offset,
                             int64_t bytes, int64_t *pnum)
 {
-    BlockDriverState *intermediate;
-    int ret;
-    int64_t n = bytes;
-
-    assert(base || !include_base);
-
-    intermediate = top;
-    while (include_base || intermediate != base) {
-        int64_t pnum_inter;
-        int64_t size_inter;
-
-        assert(intermediate);
-        ret = bdrv_is_allocated(intermediate, offset, bytes, &pnum_inter);
-        if (ret < 0) {
-            return ret;
-        }
-        if (ret) {
-            *pnum = pnum_inter;
-            return 1;
-        }
-
-        size_inter = bdrv_getlength(intermediate);
-        if (size_inter < 0) {
-            return size_inter;
-        }
-        if (n > pnum_inter &&
-            (intermediate == top || offset + pnum_inter < size_inter)) {
-            n = pnum_inter;
-        }
-
-        if (intermediate == base) {
-            break;
-        }
-
-        intermediate = backing_bs(intermediate);
+    int ret = bdrv_common_block_status_above(top, base, include_base, false,
+                                             offset, bytes, pnum, NULL, NULL);
+    if (ret < 0) {
+        return ret;
     }
 
-    *pnum = n;
-    return 0;
+    return !!(ret & BDRV_BLOCK_ALLOCATED);
 }
 
 typedef struct BdrvVmstateCo {
-- 
2.21.0

[PATCH v3 5/5] iotests: add commit top->base cases to 274

[Vladimir Sementsov-Ogievskiy]

These cases are fixed by previous patches around block_status and
is_allocated.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 tests/qemu-iotests/274     | 20 ++++++++++++
 tests/qemu-iotests/274.out | 65 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 85 insertions(+)

diff --git a/tests/qemu-iotests/274 b/tests/qemu-iotests/274
index 5d1bf34dff..e910455f13 100755
--- a/tests/qemu-iotests/274
+++ b/tests/qemu-iotests/274
@@ -115,6 +115,26 @@ with iotests.FilePath('base') as base, \
     iotests.qemu_io_log('-c', 'read -P 1 0 %d' % size_short, mid)
     iotests.qemu_io_log('-c', 'read -P 0 %d %d' % (size_short, size_diff), mid)
 
+    iotests.log('=== Testing qemu-img commit (top -> base) ===')
+
+    create_chain()
+    iotests.qemu_img_log('commit', '-b', base, top)
+    iotests.img_info_log(base)
+    iotests.qemu_io_log('-c', 'read -P 1 0 %d' % size_short, base)
+    iotests.qemu_io_log('-c', 'read -P 0 %d %d' % (size_short, size_diff), base)
+
+    iotests.log('=== Testing QMP active commit (top -> base) ===')
+
+    create_chain()
+    with create_vm() as vm:
+        vm.launch()
+        vm.qmp_log('block-commit', device='top', base_node='base',
+                   job_id='job0', auto_dismiss=False)
+        vm.run_job('job0', wait=5)
+
+    iotests.img_info_log(mid)
+    iotests.qemu_io_log('-c', 'read -P 1 0 %d' % size_short, base)
+    iotests.qemu_io_log('-c', 'read -P 0 %d %d' % (size_short, size_diff), base)
 
     iotests.log('== Resize tests ==')
 
diff --git a/tests/qemu-iotests/274.out b/tests/qemu-iotests/274.out
index d24ff681af..9806dea8b6 100644
--- a/tests/qemu-iotests/274.out
+++ b/tests/qemu-iotests/274.out
@@ -129,6 +129,71 @@ read 1048576/1048576 bytes at offset 0
 read 1048576/1048576 bytes at offset 1048576
 1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 
+=== Testing qemu-img commit (top -> base) ===
+Formatting 'TEST_DIR/PID-base', fmt=qcow2 size=2097152 cluster_size=65536 lazy_refcounts=off refcount_bits=16 compression_type=zlib
+
+Formatting 'TEST_DIR/PID-mid', fmt=qcow2 size=1048576 backing_file=TEST_DIR/PID-base cluster_size=65536 lazy_refcounts=off refcount_bits=16 compression_type=zlib
+
+Formatting 'TEST_DIR/PID-top', fmt=qcow2 size=2097152 backing_file=TEST_DIR/PID-mid cluster_size=65536 lazy_refcounts=off refcount_bits=16 compression_type=zlib
+
+wrote 2097152/2097152 bytes at offset 0
+2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+Image committed.
+
+image: TEST_IMG
+file format: IMGFMT
+virtual size: 2 MiB (2097152 bytes)
+cluster_size: 65536
+Format specific information:
+    compat: 1.1
+    compression type: zlib
+    lazy refcounts: false
+    refcount bits: 16
+    corrupt: false
+
+read 1048576/1048576 bytes at offset 0
+1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+read 1048576/1048576 bytes at offset 1048576
+1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+=== Testing QMP active commit (top -> base) ===
+Formatting 'TEST_DIR/PID-base', fmt=qcow2 size=2097152 cluster_size=65536 lazy_refcounts=off refcount_bits=16 compression_type=zlib
+
+Formatting 'TEST_DIR/PID-mid', fmt=qcow2 size=1048576 backing_file=TEST_DIR/PID-base cluster_size=65536 lazy_refcounts=off refcount_bits=16 compression_type=zlib
+
+Formatting 'TEST_DIR/PID-top', fmt=qcow2 size=2097152 backing_file=TEST_DIR/PID-mid cluster_size=65536 lazy_refcounts=off refcount_bits=16 compression_type=zlib
+
+wrote 2097152/2097152 bytes at offset 0
+2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+{"execute": "block-commit", "arguments": {"auto-dismiss": false, "base-node": "base", "device": "top", "job-id": "job0"}}
+{"return": {}}
+{"execute": "job-complete", "arguments": {"id": "job0"}}
+{"return": {}}
+{"data": {"device": "job0", "len": 1048576, "offset": 1048576, "speed": 0, "type": "commit"}, "event": "BLOCK_JOB_READY", "timestamp": {"microseconds": "USECS", "seconds": "SECS"}}
+{"data": {"device": "job0", "len": 1048576, "offset": 1048576, "speed": 0, "type": "commit"}, "event": "BLOCK_JOB_COMPLETED", "timestamp": {"microseconds": "USECS", "seconds": "SECS"}}
+{"execute": "job-dismiss", "arguments": {"id": "job0"}}
+{"return": {}}
+image: TEST_IMG
+file format: IMGFMT
+virtual size: 1 MiB (1048576 bytes)
+cluster_size: 65536
+backing file: TEST_DIR/PID-base
+Format specific information:
+    compat: 1.1
+    compression type: zlib
+    lazy refcounts: false
+    refcount bits: 16
+    corrupt: false
+
+read 1048576/1048576 bytes at offset 0
+1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+read 1048576/1048576 bytes at offset 1048576
+1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
 == Resize tests ==
 === preallocation=off ===
 Formatting 'TEST_DIR/PID-base', fmt=qcow2 size=6442450944 cluster_size=65536 lazy_refcounts=off refcount_bits=16 compression_type=zlib
-- 
2.21.0

Re: [PATCH v3 1/5] block/io: fix bdrv_co_block_status_above

[Eric Blake]

On 5/20/20 3:35 AM, Vladimir Sementsov-Ogievskiy wrote:
> bdrv_co_block_status_above has several design problems with handling
> short backing files:
> 
> 1. With want_zeros=true, it may return ret with BDRV_BLOCK_ZERO but
> without BDRV_BLOCK_ALLOCATED flag, when actually short backing file
> which produces these after-EOF zeros is inside requested backing
> sequence.
> 
> 2. With want_zero=false, it may return pnum=0 prior to actual EOF,
> because of EOF of short backing file.
> 
> Fix these things, making logic about short backing files clearer.
> 
> With fixed bdrv_block_status_above we also have to improve is_zero in
> qcow2 code, otherwise iotest 154 will fail, because with this patch we
> stop to merge zeros of different types (produced by fully unallocated
> in the whole backing chain regions vs produced by short backing files).
> 
> Note also, that this patch leaves for another day the general problem
> around block-status: misuse of BDRV_BLOCK_ALLOCATED as is-fs-allocated
> vs go-to-backing.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   block/io.c    | 39 ++++++++++++++++++++++++++++++---------
>   block/qcow2.c | 16 ++++++++++++++--
>   2 files changed, 44 insertions(+), 11 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>


> +++ b/block/qcow2.c
> @@ -3827,8 +3827,20 @@ static bool is_zero(BlockDriverState *bs, int64_t offset, int64_t bytes)
>       if (!bytes) {
>           return true;
>       }
> -    res = bdrv_block_status_above(bs, NULL, offset, bytes, &nr, NULL, NULL);
> -    return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == bytes;
> +
> +    /*
> +     * bdrv_block_status_above doesn't merge different types of zeros, for
> +     * example, zeros which comes from the region which is unallocated in

s/comes/come/

> +     * the whole backing chain, and zeros which comes because of short backing

and again, also s/of/of a/

> +     * file. So, we need a loop.
> +     */
> +    do {
> +        res = bdrv_block_status_above(bs, NULL, offset, bytes, &nr, NULL, NULL);
> +        offset += nr;
> +        bytes -= nr;
> +    } while (res >= 0 && (res & BDRV_BLOCK_ZERO) && nr && bytes);
> +
> +    return res >= 0 && (res & BDRV_BLOCK_ZERO) && bytes == 0;
>   }
>   
>   static coroutine_fn int qcow2_co_pwrite_zeroes(BlockDriverState *bs,
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

Re: [PATCH v3 2/5] block/io: bdrv_common_block_status_above: support include_base

[Eric Blake]

On 5/20/20 3:35 AM, Vladimir Sementsov-Ogievskiy wrote:
> In order to reuse bdrv_common_block_status_above in
> bdrv_is_allocated_above, let's support include_base parameter.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Reviewed-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   block/io.c | 19 ++++++++++++++-----
>   1 file changed, 14 insertions(+), 5 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

Re: [PATCH v3 3/5] block/io: bdrv_common_block_status_above: support bs == base

[Eric Blake]

On 5/20/20 3:35 AM, Vladimir Sementsov-Ogievskiy wrote:
> We are going to reuse bdrv_common_block_status_above in
> bdrv_is_allocated_above. bdrv_is_allocated_above may be called with
> include_base == false and still bs == base (for ex. from img_rebase()).
> 
> So, support this corner case.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Reviewed-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   block/io.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

> diff --git a/block/io.c b/block/io.c
> index ae1c806720..6f90b322f4 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -2458,7 +2458,11 @@ static int coroutine_fn bdrv_co_block_status_above(BlockDriverState *bs,
>       int ret = 0;
>       bool first = true;
>   
> -    assert(include_base || bs != base);
> +    if (!include_base && bs == base) {
> +        *pnum = bytes;
> +        return 0;
> +    }
> +
>       for (p = bs; include_base || p != base; p = backing_bs(p)) {
>           ret = bdrv_co_block_status(p, want_zero, offset, bytes, pnum, map,
>                                      file);
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

Re: [PATCH v3 4/5] block/io: fix bdrv_is_allocated_above

[Eric Blake]

On 5/20/20 3:35 AM, Vladimir Sementsov-Ogievskiy wrote:
> bdrv_is_allocated_above wrongly handles short backing files: it reports
> after-EOF space as UNALLOCATED which is wrong, as on read the data is
> generated on the level of short backing file (if all overlays has
> unallocated area at that place).
> 
> Reusing bdrv_common_block_status_above fixes the issue and unifies code
> path.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   block/io.c | 43 +++++--------------------------------------
>   1 file changed, 5 insertions(+), 38 deletions(-)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

Re: [PATCH v3 5/5] iotests: add commit top->base cases to 274

[Eric Blake]

On 5/20/20 3:35 AM, Vladimir Sementsov-Ogievskiy wrote:
> These cases are fixed by previous patches around block_status and
> is_allocated.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   tests/qemu-iotests/274     | 20 ++++++++++++
>   tests/qemu-iotests/274.out | 65 ++++++++++++++++++++++++++++++++++++++
>   2 files changed, 85 insertions(+)
> 
Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

Re: [PATCH v3 5/5] iotests: add commit top->base cases to 274

[Vladimir Sementsov-Ogievskiy]

20.05.2020 19:39, Eric Blake wrote:
> On 5/20/20 3:35 AM, Vladimir Sementsov-Ogievskiy wrote:
>> These cases are fixed by previous patches around block_status and
>> is_allocated.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> ---
>>   tests/qemu-iotests/274     | 20 ++++++++++++
>>   tests/qemu-iotests/274.out | 65 ++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 85 insertions(+)
>>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> 


Thanks a lot!

-- 
Best regards,
Vladimir