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

[Eric Blake <eblake@redhat.com>]

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 <mreitz@redhat.com>
> ---
>   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 <eblake@redhat.com>

> +
>   # 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