Re: [PATCH] iotests/108: probe loop device setup

[Eric Blake <eblake@redhat.com>]

On Tue, Oct 13, 2026 at 08:28:00PM +0200, Ilya Leoshkevich wrote:
> Running iotests/108 in a Docker container, that has passwordless sudo
> configured, fails with:
> 
>     losetup: /home/user/src/qemu/build/scratch/qcow2-file-108/t.qcow2: failed to set up loop device: No such file or directory
> 
> because it incorrectly assumes losetup is allowed to do loop device
> setup, when in reality it can only list devices.
> 
> Fix by probing loop device setup, using the test script as a backing
> file. With this, the test is correctly skipped.
> 
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  tests/qemu-iotests/108 | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/tests/qemu-iotests/108 b/tests/qemu-iotests/108
> index 1de718188aa..adbaaf87095 100755
> --- a/tests/qemu-iotests/108
> +++ b/tests/qemu-iotests/108
> @@ -53,7 +53,8 @@ _supported_os Linux
>  _unsupported_imgopts 'refcount_bits=\([^1]\|.\([^6]\|$\)\)' data_file
>  
>  # This test either needs sudo -n losetup or FUSE exports to work
> -if sudo -n losetup &>/dev/null; then
> +if probe_dev=$(sudo -n losetup -r --show -f "$0" 2>/dev/null); then
> +    sudo -n losetup -d "$probe_dev"

Is 'sudo -n losetup -f' a simpler test?  It prints out the next
/dev/loopN value available only if a mount would succeed, which means
that it is a stronger test than the existing 'sudo -n losetup', but
also does not require a subsequent cleanup.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org