Add the ability to query mount options in statmount

Hello,

Currently if you want to get mount options for a mount and you're using
statmount(), you still have to open /proc/mounts to parse the mount options.
statmount() does have the ability to store an arbitrary string however,
additionally the way we do that is with a seq_file, which is also how we use
->show_options for the individual file systems.

Extent statmount() to have a flag for fetching the mount options of a mount.
This allows users to not have to parse /proc mount for anything related to a
mount.  I've extended the existing statmount() test to validate this feature
works as expected.  As you can tell from the ridiculous amount of silly string
parsing, this is a huge win for users and climate change as we will no longer
have to waste several cycles parsing strings anymore.

This is based on my branch that extends listmount/statmount to walk into foreign
namespaces.  Below are links to that posting, that branch, and this branch to
make it easier to review.

https://lore.kernel.org/linux-fsdevel/cover.1719243756.gi...
https://github.com/josefbacik/linux/tree/listmount.combined
https://github.com/josefbacik/linux/tree/statmount-opts

Thanks,

Josef

Josef Bacik (4):
  fs: rename show_mnt_opts -> show_vfsmnt_opts
  fs: add a helper to show all the options for a mount
  fs: export mount options via statmount()
  sefltests: extend the statmount test for mount options

 fs/internal.h                                 |   5 +
 fs/namespace.c                                |   7 +
 fs/proc_namespace.c                           |  29 ++--
 include/uapi/linux/mount.h                    |   3 +-
 .../filesystems/statmount/statmount_test.c    | 131 +++++++++++++++++-
 5 files changed, 164 insertions(+), 11 deletions(-)

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2.43.0