[PATCH v2 0/2] ceph: add debugfs entries signifying new mount syntax support

[Venky Shankar <vshankar@redhat.com>]

v2:
 - export ceph_debugfs_dir
 - include v1 mount support debugfs entry
 - create debugfs entries under /<>/ceph/client_features dir

[This is based on top of new mount syntax series]

Patrick proposed the idea of having debugfs entries to signify if
kernel supports the new (v2) mount syntax. The primary use of this
information is to catch any bugs in the new syntax implementation.

This would be done as follows::

The userspace mount helper tries to mount using the new mount syntax
and fallsback to using old syntax if the mount using new syntax fails.
However, a bug in the new mount syntax implementation can silently
result in the mount helper switching to old syntax.

So, the debugfs entries can be relied upon by the mount helper to
check if the kernel supports the new mount syntax. Cases when the
mount using the new syntax fails, but the kernel does support the
new mount syntax, the mount helper could probably log before switching
to the old syntax (or fail the mount altogether when run in test mode).

Debugfs entries are as follows::

    /sys/kernel/debug/ceph/
    ....
    ....
    /sys/kernel/debug/ceph/client_features
    /sys/kernel/debug/ceph/client_features/v2_mount_syntax
    /sys/kernel/debug/ceph/client_features/v1_mount_syntax
    ....
    ....

Venky Shankar (2):
  libceph: export ceph_debugfs_dir for use in ceph.ko
  ceph: add debugfs entries for mount syntax support

 fs/ceph/debugfs.c            | 36 ++++++++++++++++++++++++++++++++++++
 fs/ceph/super.c              |  3 +++
 fs/ceph/super.h              |  2 ++
 include/linux/ceph/debugfs.h |  2 ++
 net/ceph/debugfs.c           |  3 ++-
 5 files changed, 45 insertions(+), 1 deletion(-)

-- 
2.27.0