O_XATTR support in FreeBSD?

[Rick Macklem]

Pedro Giffuni wrote:
> On 23.11.2013 02:13, Cedric Blancher wrote:
> > On 22 November 2013 20:55, Pedro Giffuni <pfg at freebsd.org> wrote:
> >> Well ...
> >>
> >> According to:
> >>
> >> https://wiki.freebsd.org/ZFS
> >>
> >> We do support Extended Attributes on ZFS but they differ from the
> >> ones in
> >> Solaris (and Linux).
> > Well, we need the one specified in the NFSv4 standard. The Linux
> > extended attributes are pretty much useless because they are size
> > restricted (typical attribute size here is in the GB range, and for
> > example NIH and CERN have even much bigger sizes), can't be
> > accessed
> > like normal files and are incompatible to Window's Alternate
> > Streams.
> >
> > Ced
> 
> I was unaware of a standard for EA beyond the old posix draft.
> The reason for Extended Attributes is supporting ACL and we support
> both
> the draft posix and the NFS/win style ACLs.
> 
Interestingly, FreeBSD has a VOP_OPENEXTATTR() but no syscall
that uses it nor support for it in ZFS. (I'm just guessing it
was intended for an openat(2) syscall at some time?)
Btw Cedric, if you had mentioned "subfiles" or "fork files" in your
subject line, you might have gotten a better answer. I, for one,
didn't know what O_XATTR is. I also always get confused w.r.t. what
to call these beasts. (NFSv4 calls the named attributes.)

Btw, apps can use extended attributes (the limited sized
atomically stored/read kind). They aren't just for
storing ACLs.

> Not sure about the status of NFSv4. The guys in the posix-1e list
> should
> know better.
> 
The NFSv4 implementation in FreeBSD does not support it, although
adding it wouldn't be hard if someone figures out how to do the
syscall and adds support for the VOP()s in ZFS. (I'm not volunteering
to do the latter. I have plenty of other stuff on my to-do list;-)

rick

> regards,
> 
> Pedro.
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