Re: [PATCH v6 01/11] fstests: add _loop_image_create_clone() helper

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Jun 08, 2026 at 10:39:04PM +0800, Anand Suveer Jain wrote:
> On 29/5/26 12:27, Darrick J. Wong wrote:
> > On Thu, May 28, 2026 at 12:05:32PM +0800, Anand Jain wrote:
> > > Introduce _loop_image_create_clone() and _loop_image_destroy() to mkfs an
> > > image file and clone it to another image file, and attach a loop device to
> > > them. And its destroy part.
> > > 
> > > Signed-off-by: Anand Jain <asj@kernel.org>
> > > ---
> > >  common/rc | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 63 insertions(+)
> > > 
> > > diff --git a/common/rc b/common/rc
> > > index 79189e7e6e94..d7e3e0bdfb1e 100644
> > > --- a/common/rc
> > > +++ b/common/rc
> > > @@ -1520,6 +1520,69 @@ _scratch_resvblks()
> > >  	esac
> > >  }
> > > +# Create a small loop image, run an optional tuning function ($2) on it,
> > > +# clone it, and attach both to loop devices, returned in ($1).
> > > +# Args:
> > > +#   $1: Nameref to return the array of allocated loop devices [base, clone].
> > > +#   $2: Optional callback function to tune the base filesystem before cloning.
> > > +_loop_image_create_clone()
> > > +{
> > > +	local -n _ret=$1
> > 
> > That switch   ^^ is very clever.  I always wondered how one did indirect
> > variables in bash.
> > 
> > > +	local pre_clone_tune_func="$2"
> > > +	local img_file=$TEST_DIR/${seq}.img
> > > +	local img_file_clone=$TEST_DIR/${seq}_clone.img
> > > +	local size=$(_small_fs_size_mb 128) # Smallest possible
> > > +	local loop_devs
> > > +
> > > +	# Since we copy the block device image, we keep its size small.
> > > +	_require_fs_space $TEST_DIR $((size * 1024))
> > > +
> > > +	_create_file_sized $((size * 1024 * 1024)) $img_file ||
> > > +				_fail "Failed: Create $img_file $size"
> > > +
> > > +	loop_devs=$(_create_loop_device $img_file)
> > > +	_ret=($loop_devs)
> > 
> > Should this check that a loopdev actually got created?
> > 
> 
> Hmm, in the function _create_loop_device(), we are
> calling _fail if create fails, so no need to duplicate, right?

Oh right.  Question withdrawn.

> > > +	case $FSTYP in
> > > +	xfs)
> > > +		_mkfs_dev "-s size=4096" ${loop_devs[0]}
> > > +		;;
> > > +	btrfs)
> > > +		_mkfs_dev ${loop_devs[0]}
> > > +		;;
> > > +	*)
> > > +		_mkfs_dev ${loop_devs[0]}
> > > +		;;
> > > +	esac
> > > +
> > > +	# Only execute if the function argument is not empty
> > > +	if [ -n "$pre_clone_tune_func" ]; then
> > > +		$pre_clone_tune_func ${loop_devs[0]}
> > > +	fi
> > > +
> > > +	sync ${loop_devs[0]}
> > > +	cp $img_file $img_file_clone
> > > +
> 
> 
> > > +	loop_devs="$loop_devs $(_create_loop_device $img_file_clone)"
> > 
> > 	local lodev="$(_create_loop_device ...)"
> > 
> > 	test -z "$lodev" && _fail "second loopdev not created"
> > 	_ret+=("$lodev")
> > 
> > ?
> 
> If the second `_create_loop_device()` happens to fail, it will
> already have called `_fail`, so "second loopdev..." won't be
> used at all.

<nod> Both comments withdrawn :)

--D

> 
> Thanks, Anand
> 
> 
> 
> > > +
> > > +	_ret=($loop_devs)
> > > +}
> > > +
> > > +# Teardown loop devices and delete their underlying backing image files.
> > > +# Accepts a list of loop device paths (e.g., /dev/loop0 /dev/loop1).
> > > +_loop_image_destroy()
> > > +{
> > > +	for d in "$@"; do
> > > +		# Retrieve the path of the backing file
> > > +		local f=$(losetup --noheadings --output BACK-FILE $d)
> > > +
> > > +		# Detach the loop device from the backing file
> > > +		_destroy_loop_device "$d"
> > > +
> > > +		# Clean up the backing disk image file
> > > +		[ -n "$f" ] && rm -f "$f"
> > > +	done
> > > +}
> > >  # Repair scratch filesystem.  Returns 0 if the FS is good to go (either no
> > >  # errors found or errors were fixed) and nonzero otherwise; also spits out
> > > -- 
> > > 2.43.0
> > > 
> > > 
> 
>