lockd: unlock lockd locks associated with a given server ip

For high-availability NFS service, we generally need to be able to drop
file locks held on the exported filesystem before moving clients to a
new server.  Currently the only way to do that is by shutting down lockd
entirely, which is often undesireable (for example, if you want to
continue exporting other filesystems).

This patch allows the administrator to release all locks held by clients
accessing the client through a given server ip address, by echoing that
address to a new file, /proc/fs/nfsd/unlock_ip, as in:

shell> echo 10.1.1.2 > /proc/fs/nfsd/unlock_ip

The expected sequence of events can be:
1. Tear down the IP address
2. Unexport the path
3. Write IP to /proc/fs/nfsd/unlock_ip to unlock files
4. Signal peer to begin take-over.

For now we only support IPv4 addresses and NFSv2/v3 (NFSv4 locks are not
affected).

Also, if unmounting the filesystem is required, we assume at step 3 that
clients using the given server ip are the only clients holding locks on
the given filesystem; otherwise, an additional patch is required to
allow revoking all locks held by lockd on a given filesystem.

Signed-off-by: S. Wendy Cheng <wcheng@redhat.com>
Cc: Lon Hohberger  <lhh@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

 fs/lockd/svcsubs.c          |   66 +++++++++++++++++++++++++++++++++++++++-----
 fs/nfsd/nfsctl.c            |   65 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/lockd/lockd.h |    7 ++++
 3 files changed, 131 insertions(+), 7 deletions(-)

1 files changed, 31 insertions, 5 deletions

diff --git a/fs/lockd/svcsubs.c b/fs/lockd/svcsubs.c
index dbbefbcd6712..1adcf93cb6e6 100644
--- a/fs/lockd/svcsubs.c
+++ b/fs/lockd/svcsubs.c
@@ -18,6 +18,8 @@
 #include <linux/lockd/lockd.h>
 #include <linux/lockd/share.h>
 #include <linux/lockd/sm_inter.h>
+#include <linux/module.h>
+#include <linux/mount.h>
 
 #define NLMDBG_FACILITY         NLMDBG_SVCSUBS
 
@@ -230,7 +232,7 @@ nlm_file_inuse(struct nlm_file *file)
  * Loop over all files in the file table.
  */
 static int
-nlm_traverse_files(struct nlm_host *host, nlm_host_match_fn_t match)
+nlm_traverse_files(void *data, nlm_host_match_fn_t match)
 {
         struct hlist_node *pos, *next;
         struct nlm_file *file;
@@ -244,7 +246,7 @@ nlm_traverse_files(struct nlm_host *host, nlm_host_match_fn_t match)
 
                         /* Traverse locks, blocks and shares of this file
                          * and update file->f_locks count */
-                        if (nlm_inspect_file(host, file, match))
+                        if (nlm_inspect_file(data, file, match))
                                 ret = 1;
 
                         mutex_lock(&nlm_file_mutex);
@@ -303,21 +305,27 @@ nlm_release_file(struct nlm_file *file)
  *      Used by nlmsvc_invalidate_all
  */
 static int
-nlmsvc_mark_host(struct nlm_host *host, struct nlm_host *dummy)
+nlmsvc_mark_host(void *data, struct nlm_host *dummy)
 {
+        struct nlm_host *host = data;
+
         host->h_inuse = 1;
         return 0;
 }
 
 static int
-nlmsvc_same_host(struct nlm_host *host, struct nlm_host *other)
+nlmsvc_same_host(void *data, struct nlm_host *other)
 {
+        struct nlm_host *host = data;
+
         return host == other;
 }
 
 static int
-nlmsvc_is_client(struct nlm_host *host, struct nlm_host *dummy)
+nlmsvc_is_client(void *data, struct nlm_host *dummy)
 {
+        struct nlm_host *host = data;
+
         if (host->h_server) {
                 /* we are destroying locks even though the client
                  * hasn't asked us too, so don't unmonitor the
@@ -370,3 +378,21 @@ nlmsvc_invalidate_all(void)
          */
         nlm_traverse_files(NULL, nlmsvc_is_client);
 }
+
+static int
+nlmsvc_match_ip(void *datap, struct nlm_host *host)
+{
+        __be32 *server_addr = datap;
+
+        return host->h_saddr.sin_addr.s_addr == *server_addr;
+}
+
+int
+nlmsvc_unlock_all_by_ip(__be32 server_addr)
+{
+        int ret;
+        ret = nlm_traverse_files(&server_addr, nlmsvc_match_ip);
+        return ret ? -EIO : 0;
+
+}
+EXPORT_SYMBOL_GPL(nlmsvc_unlock_all_by_ip);