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Re: [PATCH 2/3] iotests: Disable 125 on broken XFS versions


From: Eric Blake
Subject: Re: [PATCH 2/3] iotests: Disable 125 on broken XFS versions
Date: Wed, 25 Sep 2019 16:28:44 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0

On 9/25/19 1:32 PM, Max Reitz wrote:
And by that I mean all XFS versions, as far as I can tell.  All details
are in the comment below.

We never noticed this problem because we only read the first number from
qemu-img info's "disk size" output -- and that is effectively useless,
because qemu-img prints a human-readable value (which generally includes
a decimal point).  That will be fixed in the next patch.

Signed-off-by: Max Reitz <address@hidden>
---
  tests/qemu-iotests/125 | 40 ++++++++++++++++++++++++++++++++++++++++
  1 file changed, 40 insertions(+)

diff --git a/tests/qemu-iotests/125 b/tests/qemu-iotests/125
index df328a63a6..0ef51f1e21 100755
--- a/tests/qemu-iotests/125
+++ b/tests/qemu-iotests/125
@@ -49,6 +49,46 @@ if [ -z "$TEST_IMG_FILE" ]; then
      TEST_IMG_FILE=$TEST_IMG
  fi
+# Test whether we are running on a broken XFS version. There is this
+# bug:
+
+# $ rm -f foo
+# $ touch foo
+# $ block_size=4096 # Your FS's block size
+# $ fallocate -o $((block_size / 2)) -l $block_size foo
+# $ LANG=C xfs_bmap foo | grep hole
+#         1: [8..15]: hole
+#
+# The problem is that the XFS driver rounds down the offset and
+# rounds up the length to the block size, but independently.

Eww. I concur you uncovered a bug.  Have you reported this to xfs folks?

+
+touch "$TEST_IMG_FILE"
+# Assuming there is no FS with a block size greater than 64k
+fallocate -o 65535 -l 2 "$TEST_IMG_FILE"
+len0=$(get_image_size_on_host)
+
+# Write to something that in theory we have just fallocated
+# (Thus, the on-disk size should not increase)
+poke_file "$TEST_IMG_FILE" 65536 42
+len1=$(get_image_size_on_host)
+
+if [ $len1 -gt $len0 ]; then
+    _notrun "the test filesystem's fallocate() is broken"
+fi
+
+rm -f "$TEST_IMG_FILE"

Reviewed-by: Eric Blake <address@hidden>

+
  # Generally, we create some image with or without existing preallocation and
  # then resize it. Then we write some data into the image and verify that its
  # size does not change if we have used preallocation.


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



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