NFSD: Add NFSD_CMD_UNLOCK_EXPORT netlink command

When a filesystem is exported to NFS clients, NFSv4 state
(opens, locks, delegations, layouts) holds references that
prevent the underlying filesystem from being unmounted.
NFSD_CMD_UNLOCK_FILESYSTEM addresses this at superblock
granularity, but administrators unexporting a single path on a
shared filesystem (e.g., one of several exports on the same device)
need finer control.

Add NFSD_CMD_UNLOCK_EXPORT, which revokes NFSv4 state acquired
through exports of a specific path.  Matching is by path identity
(dentry + vfsmount) via the sc_export field on each nfs4_stid,
so multiple svc_export objects for the same path -- one per
auth_domain -- are handled correctly without requiring the caller
to name a specific client.

The command takes a single "path" attribute.  Userspace (exportfs
-u) sends this after removing the last client for a given path,
enabling the underlying filesystem to be unmounted.  When multiple
clients share an export path, individual unexports do not trigger
state revocation; only the final one does.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Dai Ngo <dai.ngo@oracle.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/Documentation/netlink/specs/nfsd.yaml b/Documentation/netlink/specs/nfsd.yaml
index e121c54033a0..8f36fadd68f7 100644
--- a/Documentation/netlink/specs/nfsd.yaml
+++ b/Documentation/netlink/specs/nfsd.yaml
@@ -317,6 +317,19 @@ attribute-sets:
         name: path
         type: string
         doc: Filesystem path whose state should be released.
+  -
+    name: unlock-export
+    attributes:
+      -
+        name: path
+        type: string
+        doc: >-
+          Export path whose NFSv4 state should be revoked.
+          All state (opens, locks, delegations, layouts) acquired
+          through any export of this path is revoked, regardless
+          of which client holds the state. Intended for use after
+          all clients have been unexported from a given path,
+          enabling the underlying filesystem to be unmounted.
 
 operations:
   list:
@@ -489,6 +502,20 @@ operations:
         request:
           attributes:
             - path
+    -
+      name: unlock-export
+      doc: >-
+        Revoke NFSv4 state acquired through exports of a given path.
+        Unlike unlock-filesystem, which operates at superblock granularity,
+        this command targets only state associated with a specific export
+        path. Userspace (exportfs -u) sends this after removing the last
+        client for a path so the underlying filesystem can be unmounted.
+      attribute-set: unlock-export
+      flags: [admin-perm]
+      do:
+        request:
+          attributes:
+            - path
 
 mcast-groups:
   list: