Re: RFC: Solaris style extended attributes for FreeBSD

On Tue, Apr 22, 2025 at 3:34 AM Cedric Blancher
<[email protected]> wrote:
>
> On Sun, 9 Mar 2025 at 00:02, Rick Macklem <[email protected]> wrote:
> >
> > First off, I cross posted because I don't think many read freebsd-arch@.
> > There seems to be a nice market for Solaris style extended attributes.
> > Since ZFS is already wired for them, adding the basics is pretty
> > straightforward. I am not suggesting that they should replace the
> > current FreeBSD extended attributes.
> >
> > For those not familiar with them (I am not very familiar myself;-),
> > a Solaris style extended attribute is in a directory that hangs off
> > the file object and the entries in the directory (the attributes) can
> > be manipulated with open/read/write/lseek just like a regular file.
> > (They can be as large as a regular file, but there is no atomicity
> > guarantees.)
> >
> > At this point I have a couple of rough patches:
> > https://people.freebsd.org/~rmacklem/xattr.patch - the VFS/ZFS part
> > https://people.freebsd.org/~rmacklem/nfs-xattr.patch - the NFSv4 part
>
> Any timeframe when
> https://people.freebsd.org/~rmacklem/nfs-xattr.patch will land in
> FreeBSD?
Should be in main in a week or so. I have already done one patch
commit, but there are a few more needed.

On the bigger picture...
I have finally gotten Solaris going in a VM so that I could test stuff
on it and have found a couple of incompatibilities:
- I required O_CREAT for
   nameddir_fd = openat(file_fd, ".", O_NAMEDATTR, 0);
   to create the named attribute if it did not already exist.
   Solaris does not require O_CREAT for this case (when used
   with O_XATTR) and actually returns EINVAL.
   Solaris just creates the directory if it does not already exist.

   Changing this is a trivial 2 line patch and I think being Solaris
   compatible makes sense. I required the O_CREAT, since I
   was thinking the syscall without it could be used to test to see
   if the named attribute directory exists, but I am not sure if that
   is useful?

Do others think I should change the behavior to be Solaris compatible?

- Solaris allows hard links to be created to a named attribute.
  I did not allow this, since I was concerned that having links to the
  same attribute for multiple file objects might be confusing.

Do others think I should allow them?

Thanks for any input, rick

>
> Ced
> --
> Cedric Blancher <[email protected]>
> [https://plus.google.com/u/0/+CedricBlancher/]
> Institute Pasteur