Re: [PATCH 0/2] Support for posix ACLs in fuse

[Seth Forshee <seth.forshee@canonical.com>]

On Wed, Sep 21, 2016 at 10:30:14AM +0200, Miklos Szeredi wrote:
> [Adding Andreas Gruenbacher to Cc]
> 
> On Mon, Aug 29, 2016 at 3:46 PM, Seth Forshee
> <seth.forshee@canonical.com> wrote:
> > Hi Miklos,
> >
> > Here's an updated set of patches for supporting posix ACLs in fuse. I
> > think I've incorporated all the feedback from the last RFC series, and
> > so I've dropped the RFC this time.
> 
> Pushed, with minor changes, to
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git#for-next
> 
> Please verify that I didn't break it.

I've reviewed the changes and they seem okay, still need to test.

> > I also pushed to github the changes I made to libfuse for testing this.
> > They're a little rough and probably not 100% complete, but it is
> > sufficient for exercising the functionality of these patches with
> > fusexmp.
> >
> >  https://github.com/sforshee/libfuse/tree/posix-acl
> 
> As for the libfuse part:
> 
> 1) Please don't mess with fusexmp.c.  The added code is really an
> anti-example.  Posix acls will will work fine in such pass-through
> filesystems without doing anything.  The added complexity just makes
> it brittle and racy without actually doing anything positive.

As you note below, it's hard to find a "real" filesystem to test it
with so fusexmp proved convenient for that. But I'll omit it when I
update the pull req.

> 2) You define some constants and structures (POSIX_ACL_*) in
> fuse_common.h that don't seem to belong there.  There's <sys/acl.h>
> that contains some parts of that, but I'm not sure how much we want to
> tie libfuse to libacl...  It's a difficult thing.  Generally I'd try
> to keep the interface as narrow as possible.  Perhaps it's enough to
> have a a function to return the equivalent mode from the xattr?

To be honest I only really meant that to serve as an example of all the
stuff that would need to happen in userspace based on the kernel
implementation. Looking now at libacl I guess it could just be expected
that filesystems will use that. It seems to provide the essentials to do
what I did with fusexmp at least, even an interface for getting the
equivalent mode (acl_equiv_mode). Not sure how well it works if e.g. a
filesystem needs to convert between the posix ACL format and some
different format native to that filesystem.

> 3) How will richacl's fit into this?

I don't know, I haven't looked at those patches closely, but in git I'm
not seeing any support for richacls in fuse yet anyhow.

Thanks,
Seth