linux-ext4 - Re: [PATCH 01/33] misc: adapt tests to handle the fuse ext[234] drivers

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Message-ID: <20251106231215.GC196366@frogsfrogsfrogs>
Date: Thu, 6 Nov 2025 15:12:15 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: Amir Goldstein <amir73il@...il.com>
Cc: zlang@...hat.com, neal@...pa.dev, fstests@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	joannelkoong@...il.com, bernd@...ernd.com
Subject: Re: [PATCH 01/33] misc: adapt tests to handle the fuse ext[234]
 drivers

On Thu, Nov 06, 2025 at 09:58:28AM +0100, Amir Goldstein wrote:
> On Wed, Nov 5, 2025 at 11:53 PM Darrick J. Wong <djwong@...nel.org> wrote:
> >
> > On Thu, Oct 30, 2025 at 10:51:06AM +0100, Amir Goldstein wrote:
> > > On Wed, Oct 29, 2025 at 2:22 AM Darrick J. Wong <djwong@...nel.org> wrote:
> > > >
> > > > From: Darrick J. Wong <djwong@...nel.org>
> > > >
> > > > It would be useful to be able to run fstests against the userspace
> > > > ext[234] driver program fuse2fs.  A convention (at least on Debian)
> > > > seems to be to install fuse drivers as /sbin/mount.fuse.XXX so that
> > > > users can run "mount -t fuse.XXX" to start a fuse driver for a
> > > > disk-based filesystem type XXX.
> > > >
> > > > Therefore, we'll adopt the practice of setting FSTYP=fuse.ext4 to
> > > > test ext4 with fuse2fs.  Change all the library code as needed to handle
> > > > this new type alongside all the existing ext[234] checks, which seems a
> > > > little cleaner than FSTYP=fuse FUSE_SUBTYPE=ext4, which also would
> > > > require even more treewide cleanups to work properly because most
> > > > fstests code switches on $FSTYP alone.
> > > >
> > >
> > > I agree that FSTYP=fuse.ext4 is cleaner than
> > > FSTYP=fuse FUSE_SUBTYPE=ext4
> > > but it is not extendable to future (e.g. fuse.xfs)
> > > and it is still a bit ugly.
> > >
> > > Consider:
> > > FSTYP=fuse.ext4
> > > MKFSTYP=ext4
> > >
> > > I think this is the correct abstraction -
> > > fuse2fs/ext4 are formatted that same and mounted differently
> > >
> > > See how some of your patch looks nicer and naturally extends to
> > > the imaginary fuse.xfs...
> >
> > Maybe I'd rather do it the other way around for fuse4fs:
> >
> > FSTYP=ext4
> > MOUNT_FSTYP=fuse.ext4
> >
> 
> Sounds good. Will need to see the final patch.
> 
> > (obviously, MOUNT_FSTYP=$FSTYP if the test runner hasn't overridden it)
> >
> > Where $MOUNT_FSTYP is what you pass to mount -t and what you'd see in
> > /proc/mounts.  The only weirdness with that is that some of the helpers
> > will end up with code like:
> >
> >         case $FSTYP in
> >         ext4)
> >                 # do ext4 stuff
> >                 ;;
> >         esac
> >
> >         case $MOUNT_FSTYP in
> >         fuse.ext4)
> >                 # do fuse4fs stuff that overrides ext4
> >                 ;;
> >         esac
> >
> > which would be a little weird.
> >
> 
> Sounds weird, but there is always going to be weirdness
> somewhere - need to pick the least weird result or most
> easy to understand code IMO.
> 
> > _scratch_mount would end up with:
> >
> >         $MOUNT_PROG -t $MOUNT_FSTYP ...
> >
> > and detecting it would be
> >
> >         grep -q -w $MOUNT_FSTYP /proc/mounts || _fail "booooo"
> >
> > Hrm?
> 
> Those look obviously nice.
> 
> Maybe the answer is to have all MOUNT_FSTYP, MKFS_FSTYP
> and FSTYP and use whichever best fits in the context.

Hrmm well I would /like/ avoid adding MKFS_FSTYP since ext4 is ext4, no
matter whether we're using the kernel or fuse42fs.  Do you have a use
case for adding such a thing?

--D

> Thanks,
> Amir.
>