backup-discard-source iotest fails on xfs, pass on ext4

[Nir Soffer]

While testing 
https://lists.nongnu.org/archive/html/qemu-block/2024-06/msg00644.html
I noticed that
this tests is failing also with master
(28b8a57ad63670aa0ce90334523dc552b13b4336).

The test succeeds with ext4, and fail with xfs.

Nir

---

Success on ext4:

$ TEST_DIR=/data/tetests/qemu-iotests/check backup-discard-source -qcow2
test-ext4/ test-xfs/
[nsoffer build (master)]$ TEST_DIR=/data/test-ext4/scratch
tests/qemu-iotests/check backup-discard-source -qcow2
QEMU          -- "/home/nsoffer/src/qemu/build/qemu-system-x86_64"
-nodefaults -display none -accel qtest
QEMU_IMG      -- "/home/nsoffer/src/qemu/build/qemu-img"
QEMU_IO       -- "/home/nsoffer/src/qemu/build/qemu-io" --cache
writeback --aio threads -f qcow2
QEMU_NBD      -- "/home/nsoffer/src/qemu/build/qemu-nbd"
IMGFMT        -- qcow2
IMGPROTO      -- file
PLATFORM      -- Linux/x86_64 sparse.local 6.9.4-100.fc39.x86_64
TEST_DIR      -- /data/test-ext4/scratch
SOCK_DIR      -- /tmp/qemu-iotests-rdoofjdc
GDB_OPTIONS   --
VALGRIND_QEMU --
PRINT_QEMU_OUTPUT --

backup-discard-source   pass       [00:14:09] [00:14:10]   0.8s
Passed all 1 iotests


Failing on xfs:

$ TEST_DIR=/data/test-xfs/scratch tests/qemu-iotests/check
backup-discard-source -qcow2
QEMU          -- "/home/nsoffer/src/qemu/build/qemu-system-x86_64"
-nodefaults -display none -accel qtest
QEMU_IMG      -- "/home/nsoffer/src/qemu/build/qemu-img"
QEMU_IO       -- "/home/nsoffer/src/qemu/build/qemu-io" --cache
writeback --aio threads -f qcow2
QEMU_NBD      -- "/home/nsoffer/src/qemu/build/qemu-nbd"
IMGFMT        -- qcow2
IMGPROTO      -- file
PLATFORM      -- Linux/x86_64 sparse.local 6.9.4-100.fc39.x86_64
TEST_DIR      -- /data/test-xfs/scratch
SOCK_DIR      -- /tmp/qemu-iotests-4j_gu404
GDB_OPTIONS   --
VALGRIND_QEMU --
PRINT_QEMU_OUTPUT --

backup-discard-source   fail       [00:15:44] [00:15:45]   0.8s
(last: 0.8s)  failed, exit status 1
--- /home/nsoffer/src/qemu/tests/qemu-iotests/tests/backup-discard-source.out
+++ 
/data/test-xfs/scratch/qcow2-file-backup-discard-source/backup-discard-source.out.bad
@@ -1,5 +1,14 @@
-..
+F.
+======================================================================
+FAIL: test_discard_cbw (__main__.TestBackup.test_discard_cbw)
+1. do backup(discard_source=True), which should inform
+----------------------------------------------------------------------
+Traceback (most recent call last):
+  File "/home/nsoffer/src/qemu/tests/qemu-iotests/tests/backup-discard-source",
line 147, in test_discard_cbw
+    self.assertLess(get_actual_size(self.vm, 'temp'), 512 * 1024)
+AssertionError: 1249280 not less than 524288
+
 ----------------------------------------------------------------------
 Ran 2 tests

-OK
+FAILED (failures=1)
Failures: backup-discard-source
Failed 1 of 1 iotests


$ xfs_info /data/test-xfs/
meta-data=/dev/mapper/data-test--xfs isize=512    agcount=4, agsize=655360 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=1, sparse=1, rmapbt=0
         =                       reflink=1    bigtime=1 inobtcount=1 nrext64=0
data     =                       bsize=4096   blocks=2621440, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0, ftype=1
log      =internal log           bsize=4096   blocks=16384, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0