[Qemu-devel] [PATCH v1 02/13] qcow2: is_zero_sectors(): return true if area is outside of backing file

[Anton Nefedov]

in such case, bdrv_get_block_status() shall return 0, *nr == 0

iotest 154 updated accordingly: write-zeroes tail alignment can be detected
as zeroes now, so pwrite_zeroes succeeds

Signed-off-by: Anton Nefedov <anton.nefe...@virtuozzo.com>
---
 block/qcow2.c              | 6 ++++--
 tests/qemu-iotests/154.out | 4 ++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 2e6a0ec..b885dfc 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2482,7 +2482,7 @@ static bool is_zero_sectors(BlockDriverState *bs, int64_t 
start,
     int64_t res;
 
     if (start + count > bs->total_sectors) {
-        count = bs->total_sectors - start;
+        count = start < bs->total_sectors ? bs->total_sectors - start : 0;
     }
 
     if (!count) {
@@ -2490,7 +2490,9 @@ static bool is_zero_sectors(BlockDriverState *bs, int64_t 
start,
     }
     res = bdrv_get_block_status_above(bs, NULL, start, count,
                                       &nr, &file);
-    return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == count;
+    return res >= 0
+        && (((res & BDRV_BLOCK_ZERO) && nr == count)
+            || nr == 0);
 }
 
 static coroutine_fn int qcow2_co_pwrite_zeroes(BlockDriverState *bs,
diff --git a/tests/qemu-iotests/154.out b/tests/qemu-iotests/154.out
index d8485ee..259340e 100644
--- a/tests/qemu-iotests/154.out
+++ b/tests/qemu-iotests/154.out
@@ -322,7 +322,7 @@ wrote 1024/1024 bytes at offset 134218240
 1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 2048/2048 bytes allocated at offset 128 MiB
 [{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
-{ "start": 134217728, "length": 2048, "depth": 0, "zero": false, "data": true, 
"offset": OFFSET}]
+{ "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 
backing_file=TEST_DIR/t.IMGFMT.base
 wrote 2048/2048 bytes at offset 134217728
 2 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -348,7 +348,7 @@ wrote 1024/1024 bytes at offset 134218240
 1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 2048/2048 bytes allocated at offset 128 MiB
 [{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
-{ "start": 134217728, "length": 2048, "depth": 0, "zero": false, "data": true, 
"offset": OFFSET}]
+{ "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 
backing_file=TEST_DIR/t.IMGFMT.base
 wrote 2048/2048 bytes at offset 134217728
 2 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-- 
2.7.4