> On Thu, Aug 09, 2012 at 04:30:21AM -0400, Tomas Racek wrote:
> > 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 $SCRATCH_DEV doesn't support discard. Has
> > anybody been working on some xfstests' standard way of
> > creating/destroying loop devices?
> >
> > I could do with something as simple as this (in common.rc):
>
> Probably a good idea given the random failures we get with loopback
> device unmounting due to the racy unmount-based automatic device
> destruction.
>
> >
> > _create_loop_device()
> > {
> > size=${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
I've missed that...
> 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.
>
> > truncate -s $size $file || _fail "Cannot create image file
> > $file"
>
> It's better to use xfs_io that introduce new external tool
> dependencies.
OK.
>
> > 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?
>
> > 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?
I wasn't aware of that. I've always used the two-step approach:
losetup /dev/loopX file
mount /dev/loopX mntpoint
and subsequent umount never destroyed loop device in my case. I tried to use only
mount file mntpoint
which then resulted in behaviour you described. Is this the rule or is some other magic in that?
> 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:
Thanks for useful comments, I appreciate that.
Tomas
>
> _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
> david@xxxxxxxxxxxxx
>
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