Revalidate caches on lock

Instead of blindly zapping the caches, attempt to revalidate them if
the server has indicated that it uses high resolution timestamps.

NFSv4 should be able to always revalidate the cache since the
protocol requires the update of the change attribute on modification of
the data.  In reality, there are servers (the Linux NFS server
for example) that do not obey this requirement and use ctime as the
basis for change attribute.  Long term, the server needs to be fixed.
At this time, and to be on the safe side, continue zapping caches if
the server indicates that it does not have a high resolution timestamp.

Signed-off-by: Ricardo Labiaga <Ricardo.Labiaga@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index c82ee7cd6288..5eef862ec187 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -124,6 +124,7 @@ struct nfs_server {
 
         struct nfs_fsid         fsid;
         __u64                   maxfilesize;    /* maximum file size */
+        struct timespec         time_delta;     /* smallest time granularity */
         unsigned long           mount_time;     /* when this fs was mounted */
         dev_t                   s_dev;          /* superblock dev numbers */
 
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index efe2eab8ac94..da7a1300dc60 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -112,6 +112,7 @@ struct nfs_fsinfo {
         __u32                   wtmult; /* writes should be multiple of this */
         __u32                   dtpref; /* pref. readdir transfer size */
         __u64                   maxfilesize;
+        struct timespec         time_delta; /* server time granularity */
         __u32                   lease_time; /* in seconds */
 };