[lustre-devel] odd behavior on lustre client listxattr for directories

[Kristen Webb]

Our backup software found an unusual result when listing xattrs for
directories.

On the client side, when requesting the buffer size for the list:
listxattr("foo", NULL, 0)               = 36 (bytes)

But when the list is actually read, it comes up short:
listxattr("foo", "trusted.link\0trusted.lma\0", 256) = 25 (bytes)

On the server side, on an ldiskfs mount, the results are more consistent.
listxattr("foo", NULL, 0)               = 25
listxattr("foo", "trusted.lma\0trusted.link\0", 256) = 25

NOTE: we run this code on lot's of FS's and have not seen this anywhere
else, yet.
According to the docs for listxattr, it is possible to get different
results on active objects
but that is not the case here.

I'm reporting this because, while it does not seem to be a problem for us
now,
I'd like to understand the "why"/ . Also, this seems like something that
may cause
problems with more complex directory xatts's which I have not tested yet.

I plan to deep-dive on this one to get more information, unless someone has
a reasonable explanation as to why the inconsistency exists and that is is
"ok".

If this is something that should be reported as a bug, just let me know and
I'll submit
one with as much detail as I can get.

Thanks!
Kris
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Mr. Kristen J. Webb
Chief Technology Officer
Teradactyl LLC.
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Phone: 1-505-338-6000
Email: kwebb at teradactyl.com
Web: http://www.teradactyl.com



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