[QEMU HCI-8.0 PATCH 6/5] VZ: iotests/nbd-commands: do not depend on cluster allocation order #VSTOR-119829

[Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>]

test_cache_copies_on_read compares qemu-img map output verbatim, but
map only merges neighbours that are contiguous in the image file.  Our
copy-on-read runs its 16M chunks concurrently since ce4a1338cf7
("block/io: copy-on-read: use aio task pool"), so the two halves of
the 32M NBD_CMD_CACHE race for cluster allocation and flakily land in
the file in swapped order:

  OK:   {start: 0,   length: 32M, depth: 0, offset:   327680}

  FAIL: {start: 0,   length: 16M, depth: 0, offset: 17104896}
        {start: 16M, length: 16M, depth: 0, offset:   327680}

Same data, same depth, only the host offsets differ.  Merge adjacent
extents of equal depth in top_extents() so that the test compares the
guest layout, not the file layout.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 tests/qemu-iotests/tests/nbd-commands | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/tests/qemu-iotests/tests/nbd-commands b/tests/qemu-iotests/tests/nbd-commands
index 4c1cd33db74..9a4a0d1ecd8 100755
--- a/tests/qemu-iotests/tests/nbd-commands
+++ b/tests/qemu-iotests/tests/nbd-commands
@@ -105,8 +105,17 @@ class TestNbdCommands(iotests.QMPTestCase):
         """Which parts of the top image are local, once qemu has let go."""
         self.disconnect()
         self.vm.shutdown()
-        return [(e['start'], e['length'], e['depth'])
-                for e in qemu_img_map(top)]
+        # Concurrent copy-on-read tasks may allocate clusters out of
+        # order, and qemu-img map does not merge neighbours that are
+        # discontiguous in the image file.  Only the guest layout
+        # matters here, so merge adjacent extents of equal depth.
+        extents = []
+        for e in qemu_img_map(top):
+            if extents and extents[-1][2] == e['depth']:
+                extents[-1][1] += e['length']
+            else:
+                extents.append([e['start'], e['length'], e['depth']])
+        return [tuple(e) for e in extents]
 
     def test_cache_copies_on_read(self):
         maximum = self.h.get_block_size(nbd.SIZE_MAXIMUM)
-- 
2.47.1