[PATCH 0/4 v2] NFSD: Pin to vfsmount for some nfsd exports cache

[Kinglong Mee <kinglongmee-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

If there are some mount points(not exported for nfs) under pseudo root,
after client's operation of those entry under the root, anyone *can't*
unmount those mount points until export cache expired.

# cat /etc/exports
/nfs/xfs        *(rw,insecure,no_subtree_check,no_root_squash)
/nfs/pnfs       *(rw,insecure,no_subtree_check,no_root_squash)
# ll /nfs/
total 0
drwxr-xr-x. 3 root root 84 Apr 21 22:27 pnfs
drwxr-xr-x. 3 root root 84 Apr 21 22:27 test
drwxr-xr-x. 2 root root  6 Apr 20 22:01 xfs
# mount /dev/sde /nfs/test
# df
Filesystem                      1K-blocks    Used Available Use% Mounted on
......
/dev/sdd                          1038336   32944   1005392   4% /nfs/pnfs
/dev/sdc                         10475520   32928  10442592   1% /nfs/xfs
/dev/sde                           999320    1284    929224   1% /nfs/test
# mount -t nfs 127.0.0.1:/nfs/ /mnt
# ll /mnt/*/
/mnt/pnfs/:
total 0
-rw-r--r--. 1 root root 0 Apr 21 22:23 attr
drwxr-xr-x. 2 root root 6 Apr 21 22:19 tmp

/mnt/xfs/:
total 0
# umount /nfs/test/
umount: /nfs/test/: target is busy
        (In some cases useful info about processes that
         use the device is found by lsof(8) or fuser(1).)

I don't think that's user expect, they want umount /nfs/test/.

It's caused by exports cache of nfsd holds the reference of
the path (here is /nfs/test/), so, it can't be umounted.

v1 --> v2,
1. Adds an option named "allow_umount" for exports allowing user
   un-mounting the filesystem where nfsd exports base on.
2. New helpers path_get_pin/path_put_unpin for path pin.
3. Update exports according to the "allow_umount" option.

Kinglong Mee (5):
  fs_pin: Fix uninitialized value in fs_pin
  fs_pin: Export functions for specific filesystem
  path: New helpers path_get_pin/path_put_unpin for path pin
  sunrpc: New helper cache_force_expire for cache cleanup
  nfsd: Allows user un-mounting filesystem where nfsd exports base on

 fs/fs_pin.c                      |  3 +++
 fs/namei.c                       | 26 ++++++++++++++++++++
 fs/nfsd/export.c                 | 52 ++++++++++++++++++++++++++++++++--------
 fs/nfsd/export.h                 | 11 ++++++++-
 include/linux/fs_pin.h           |  6 +++++
 include/linux/path.h             |  4 ++++
 include/linux/sunrpc/cache.h     | 11 +++++++++
 include/uapi/linux/nfsd/export.h |  3 ++-
 8 files changed, 104 insertions(+), 12 deletions(-)

-- 
2.4.1

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