[PATCH V2 0/2] NFSD: offer write delegation for OPEN with OPEN4_SHARE_ACCESS only

[Dai Ngo <dai.ngo@oracle.com>]

From RFC8881 does not explicitly state that server must grant write
delegation to OPEN with OPEN4_SHARE_ACCESS_WRITE only. However there
are text in the RFC that implies it is up to the server implementation
to offer write delegation for OPEN with OPEN4_SHARE_ACCESS_WRITE only.

Section 9.1.2:

  "In the case of READ, the server may perform the corresponding
   check on the access mode, or it may choose to allow READ for
   OPEN4_SHARE_ACCESS_WRITE, to accommodate clients whose WRITE
   implementation may unavoidably do (e.g., due to buffer cache
   constraints)."

Also in section 10.4.1

  "Similarly, when closing a file opened for OPEN4_SHARE_ACCESS_WRITE/
   OPEN4_SHARE_ACCESS_BOTH and if an OPEN_DELEGATE_WRITE delegation
   is in effect"

This patch series offers write delegation for OPEN with OPEN4_SHARE_ACCESS_WRITE
only. The file struct, nfs4_file and nfs4_ol_stateid are upgraded
accordingly from write only access to read/write access. When the
delegation is returned, the file struct, nfs4_file and nfs4_ol_stateid
are downgraded according to remove the read access.

-- changes from v1:
0002: The file access mode is upgraded to include read access at the time
      the delegation is granted and read access is removed when the delegation
      is returned.

 fs/nfsd/nfs4state.c | 96 +++++++++++++++++++++++++++++++++++++-----------
 fs/nfsd/state.h     |  2 +
 2 files changed, 77 insertions(+), 21 deletions(-)