xfstests: standard way of handling loop devices

Hi,

I am currently working on tests that check FITRIM implementation (251, 260 and one new I'm writing now) and I want to use loopback device as fallback if $SCRATCH_DEV doesn't support discard. Has anybody been working on some xfstests' standard way of creating/destroying loop devices?

I could do with something as simple as this (in common.rc):

_create_loop_device()

{
        size=${1}
        dev=`losetup -f`
        file="$TEST_DIR/$(basename $dev).fs"

        truncate -s $size $file || _fail "Cannot create image file $file"

        losetup $dev $file || _fail "Cannot associate $file with $dev"
        echo $dev
}

_destroy_loop_device()

{
        dev=${1}
        umount $dev 2>&1

        file=`losetup -a | grep $dev | sed -n "s/.*(\(.*\))$/\1/p"`
        losetup -d $dev && rm -f $file || _fail "Cannot destroy loop device"

Quoted 9 lines

Hi,

I am currently working on tests that check FITRIM implementation (251, 260 and one new I'm writing now) and I want to use loopback device as fallback if $SCRATCH_DEV doesn't support discard. Has anybody been working on some xfstests' standard way of creating/destroying loop devices?

I could do with something as simple as this (in common.rc):

Probably a good idea given the random failures we get with loopback device unmounting due to the racy unmount-based automatic device destruction.

Quoted 1 line

Quoted 5 lines

_create_loop_device()

{
        size=${1}
        dev=`losetup -f`
        file="$TEST_DIR/$(basename $dev).fs"

That won't work - we create loop devices with files on the scratch device, too, and some tests create more than one. This is also racy

in that two threads could both get then same next free loopback device, but I'm not sure we care about that case very much.

Quoted 2 lines

        truncate -s $size $file || _fail "Cannot create image file
        $file"

It's better to use xfs_io that introduce new external tool dependencies.

Quoted 10 lines

        losetup $dev $file || _fail "Cannot associate $file with
        $dev"
        echo $dev
}

_destroy_loop_device()

{
        dev=${1}
        umount $dev 2>&1

If unmount fails, what then?

Quoted 3 lines

        file=`losetup -a | grep $dev | sed -n "s/.*(\(.*\))$/\1/p"`
        losetup -d $dev && rm -f $file || _fail "Cannot destroy
        loop device"

And if unmount destroys the loop device automatically? That will fail the test, right?

Also, what happens if we unmount the filesystem first so we can run consistency checks on the image before we destroy it?

I'd suggest that it is the test's responsibility to create, mount, unmount, check and destroy the image file as those vary from test to test. Hence a better idea is to just use an image path/device API. i.e:

_create_loop_device()

{
	file=$1
        dev=`losetup -f`
        losetup $dev $file || _fail "Cannot associate $file with
        $dev"
        echo $dev
}

_destroy_loop_device()

{
	dev=$1
	losetup -d $dev || _fail "Cannot destroy loop device"
}

Cheers,

Dave.
--
Dave Chinner
[email protected]