NFS: report how long an NFS file system has been mounted

Add a field in nfs_server to record a timestamp when a mount succeeds.
Report the number of seconds the file system has been mounted via
nfs_show_stats().

Test plan:
Mount an NFS file system, watch the mountstats reports and compare with
clock time.

Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 6 insertions, 0 deletions

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 8ee74111e519..1b2d782374b5 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -299,6 +299,9 @@ nfs_sb_init(struct super_block *sb, rpc_authflavor_t authflavor)
                 goto out_no_root;
         }
 
+        /* mount time stamp, in seconds */
+        server->mount_time = jiffies;
+
         /* Get some general file system info */
         if (server->namelen == 0 &&
             server->rpc_ops->pathconf(server, &server->fh, &pathinfo) >= 0)
@@ -674,6 +677,8 @@ static int nfs_show_stats(struct seq_file *m, struct vfsmount *mnt)
         seq_puts(m, mnt->mnt_sb->s_flags & MS_NODIRATIME ? ",nodiratime" : "");
         nfs_show_mount_options(m, nfss, 1);
 
+        seq_printf(m, "\n\tage:\t%lu", (jiffies - nfss->mount_time) / HZ);
+
         seq_printf(m, "\n\tcaps:\t");
         seq_printf(m, "caps=0x%x", nfss->caps);
         seq_printf(m, ",wtmult=%d", nfss->wtmult);
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index d65e69a06b72..65dec21af774 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -35,6 +35,7 @@ struct nfs_server {
         char *                  hostname;       /* remote hostname */
         struct nfs_fh           fh;
         struct sockaddr_in      addr;
+        unsigned long           mount_time;     /* when this fs was mounted */
 #ifdef CONFIG_NFS_V4
         /* Our own IP address, as a null-terminated string.
          * This is used to generate the clientid, and the callback address.