On Sun, Mar 9, 2025 at 5:38 AM Andrew Walker <awal...@ixsystems.com> wrote:
>
> > 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
>
> The ZFS story is more complicated. When ZFS is configured with
> `xattr=sa`, xattrs are preferentially written into system attributes
> (SA). This was introduced IIRC primarily for performance reasons
> This allows tiny xattrs (~100 bytes) to be stored with the dnode and
> up to 64 KiB of xattrs to be stored in the dnode spill block. If
> additional space is needed then they are written using the older-style
> file-backed approach.
>
> What this means is that if someone is using this relatively common
> configuration (the default in TrueNAS and in many Linux distros), then
> the result would be that only some xattrs written via extattr would be
> visible by directly opening the ZFS attr dir. It would also introduce
> a mechanism whereby an xattr with the same name is written to two
> different ZFS locations, which would potentially cause you to see
> different xattr data depending on whether you read it from extattr or
> via the attr dir. I don't know off-hand whether this could lead to
> corruption / unexpected behavior in ZFS but if you haven't looked into
> it yet you may want to make sure you're properly handling the case
> where someone has already written SA-backed xattrs.
I am in the process of defining a new setting for the xattr property
I've called "named" which would need to be set for the Solaris style
extended attributes to work.
I am making progress on the patch and am currently working through
permissions (or authorization if you prefer).
Here is what OpenZFS appears to do currently.
I am wondering if these sound reasonable for these attributes?
- When an attr directory is created for a file object, the ownership
(uid and gid) is set to the same value as the file object.
The mode is set to 041777 (a directory with sticky bit set and
permissions for everyone. (It ignores the "mode" argument to
the open.)
--> As such, anyone who has access to the file object can access
the extended attribute directory.
- When an attribute is created in the attribute directory, the uid is
set to that of the creating process (cr_uid), the gid is set to that
of the directory (which is also the gid of the file object).
The mode is set to that of a regular file with low order mode bits
as specified by the "mode" argument to the openat() that created
it.
The mode can be changed with fchmod(2).
--> As such, access to each attribute file is controlled by the
attribute file's creator.
Any comments on the above?
A couple of other questions...
- Should subdirectories of the attribute directory be supported?
I currently do not allow this, but it appears to be supportable
by both OpenZFS and NFSv4.
- Does restricting this support to ZFS file systems with the
xattr property set to "named" sound reasonable?
Thanks for any comments, rick
ps: I have not, as yet, heard any comments w.r.t. whether or
not this should go into FreeBSD15. (No rush on this one,
but comments would be appreciated.
