[lustre-discuss] storing Lustre jobid in file xattrs: seeking feedback

[Andreas Dilger]

Hi Thomas,
thanks for working on this functionality and raising this question.

As you know, I'm inclined toward the user.job xattr, but I think it is never a good idea to unilaterally make policy decisions in the kernel that cannot be changed.

As such, it probably makes sense to have a tunable parameter like "mdt.*.job_xattr=user.job" and then this could be changed in the future if there is some conflict (e.g. some site already uses the "user.job" xattr for some other purpose).

I don't think the job_xattr should allow totally arbitrary values (e.g. overwriting trusted.lov or trusted.lma or security.* would be bad). One option is to only allow a limited selection of valid xattr namespaces, and possibly names:

  *   NONE to turn this feature off
  *   user, or trusted or system (if admin wants to restrict the ability of regular users to change this value?), with ".job" added automatically
  *   user.* (or trusted.* or system.*) to also allow specifying the xattr name

If we allow the xattr name portion to be specified (which I'm not sure about, but putting it out for completeness), it should have some reasonable limits:

  *   <= 7 characters long to avoid wasting valuable xattr space in the inode
  *   should not conflict with other known xattrs, which is tricky if we allow the name to be arbitrary. Possibly if in trusted (and system?) it should only allow trusted.job to avoid future conflicts?
  *   maybe restrict it to contain "job" (or maybe "pbs", "slurm", ...) to reduce the chance of namespace clashes in user or system? However, I'm reluctant to restrict names in user since this shouldn't have any fatal side effects (e.g. data corruption like in trusted or system), and the admin is supposed to know what they are doing...

On May 4, 2023, at 15:53, Bertschinger, Thomas Andrew Hjorth via lustre-discuss <lustre-discuss at lists.lustre.org<mailto:lustre-discuss at lists.lustre.org>> wrote:

Hello Lustre Users,

There has been interest in a proposed feature https://jira.whamcloud.com/browse/LU-13031 to store the jobid with each Lustre file at create time, in an extended attribute. An open question is which xattr namespace is to use between "user", the Lustre-specific namespace "lustre", "trusted", or even perhaps "system".

The correct namespace likely depends on how this xattr will be used. For example, will interoperability with other filesystems be important? Different namespaces have their own limitations so the correct choice depends on the use cases.

I'm looking for feedback on applications for this feature. If you have thoughts on how you could use this, please feel free to share them so that we design it in a way that meets your needs.

Thanks!

Tom Bertschinger
LANL
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Cheers, Andreas
--
Andreas Dilger
Lustre Principal Architect
Whamcloud







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