Public bug reported:

When mounting a ceph volume, mount operation fails with an IO error.
The problem is always reproducible.

Identified potential root cause as kernel endian bug:

In the function handle_session() variable @features always
contains little endian order of bytes. Just because The feature
mask sent by the MDS is little-endian (bits are packed bytewise
from left to right in encode_supported_features()).

However, test_bit(), called to check features availability, assumes
the host order of bytes in that variable. This leads to problems on
big endian architectures. Specifically it is impossible to mount
ceph volume on s390.

A fixup was proposed to convert little-endian order of bytes to the host
one. That fixup was modified by ceph maintainers to use existing
unpacking means for the conversion. The resulted patch attached.

Related discussion in the ceph-development mailing list:
https://marc.info/?l=ceph-devel&m=158815357301332&w=2

** Affects: ceph (Ubuntu)
     Importance: Undecided
     Assignee: Skipper Bug Screeners (skipper-screen-team)
         Status: New


** Tags: architecture-s39064 bugnameltc-185690 severity-high 
targetmilestone-inin2004

** Tags added: architecture-s39064 bugnameltc-185690 severity-high
targetmilestone-inin2004

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https://bugs.launchpad.net/bugs/1875863

Title:
  ceph -- Unable to mount ceph volume on s390x

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