[Bug 1875863] Proposed fixup

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** Attachment added: "Proposed fixup"
   https://bugs.launchpad.net/bugs/1875863/+attachment/5363443/+files/ceph-fix-up-endian-bug-in-managing-feature-bits.eml

** Changed in: ubuntu
     Assignee: (unassigned) => Skipper Bug Screeners (skipper-screen-team)

** Package changed: ubuntu => ceph (Ubuntu)

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

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

Status in ceph package in Ubuntu:
  New

Bug description:
  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

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