nfsd: support ext4 i_version

ext4 supports a real NFSv4 change attribute, which is bumped whenever
the ctime would be updated, including times when two updates arrive
within a jiffy of each other.  (Note that although ext4 has space for
nanosecond-precision ctime, the real resolution is lower: it actually
uses jiffies as the time-source.)  This ensures clients will invalidate
their caches when they need to.

There is some fear that keeping the i_version up-to-date could have
performance drawbacks, so for now it's turned on only by a mount option.
We hope to do something better eventually.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Cc: Theodore Tso <tytso@mit.edu>

2 files changed, 20 insertions, 4 deletions

diff --git a/include/linux/nfsd/nfsfh.h b/include/linux/nfsd/nfsfh.h
index afa19016c4a..8f641c90845 100644
--- a/include/linux/nfsd/nfsfh.h
+++ b/include/linux/nfsd/nfsfh.h
@@ -151,9 +151,15 @@ typedef struct svc_fh {
 	__u64			fh_pre_size;	/* size before operation */
 	struct timespec		fh_pre_mtime;	/* mtime before oper */
 	struct timespec		fh_pre_ctime;	/* ctime before oper */
+	/*
+	 * pre-op nfsv4 change attr: note must check IS_I_VERSION(inode)
+	 *  to find out if it is valid.
+	 */
+	u64			fh_pre_change;
 
 	/* Post-op attributes saved in fh_unlock */
 	struct kstat		fh_post_attr;	/* full attrs after operation */
+	u64			fh_post_change; /* nfsv4 change; see above */
 #endif /* CONFIG_NFSD_V3 */
 
 } svc_fh;
@@ -298,6 +304,7 @@ fill_pre_wcc(struct svc_fh *fhp)
 		fhp->fh_pre_mtime = inode->i_mtime;
 		fhp->fh_pre_ctime = inode->i_ctime;
 		fhp->fh_pre_size  = inode->i_size;
+		fhp->fh_pre_change = inode->i_version;
 		fhp->fh_pre_saved = 1;
 	}
 }
diff --git a/include/linux/nfsd/xdr4.h b/include/linux/nfsd/xdr4.h
index f80d6013fdc..d0f050f01ec 100644
--- a/include/linux/nfsd/xdr4.h
+++ b/include/linux/nfsd/xdr4.h
@@ -64,10 +64,13 @@ static inline bool nfsd4_has_session(struct nfsd4_compound_state *cs)
 
 struct nfsd4_change_info {
 	u32		atomic;
+	bool		change_supported;
 	u32		before_ctime_sec;
 	u32		before_ctime_nsec;
+	u64		before_change;
 	u32		after_ctime_sec;
 	u32		after_ctime_nsec;
+	u64		after_change;
 };
 
 struct nfsd4_access {
@@ -503,10 +506,16 @@ set_change_info(struct nfsd4_change_info *cinfo, struct svc_fh *fhp)
 {
 	BUG_ON(!fhp->fh_pre_saved || !fhp->fh_post_saved);
 	cinfo->atomic = 1;
-	cinfo->before_ctime_sec = fhp->fh_pre_ctime.tv_sec;
-	cinfo->before_ctime_nsec = fhp->fh_pre_ctime.tv_nsec;
-	cinfo->after_ctime_sec = fhp->fh_post_attr.ctime.tv_sec;
-	cinfo->after_ctime_nsec = fhp->fh_post_attr.ctime.tv_nsec;
+	cinfo->change_supported = IS_I_VERSION(fhp->fh_dentry->d_inode);
+	if (cinfo->change_supported) {
+		cinfo->before_change = fhp->fh_pre_change;
+		cinfo->after_change = fhp->fh_post_change;
+	} else {
+		cinfo->before_ctime_sec = fhp->fh_pre_ctime.tv_sec;
+		cinfo->before_ctime_nsec = fhp->fh_pre_ctime.tv_nsec;
+		cinfo->after_ctime_sec = fhp->fh_post_attr.ctime.tv_sec;
+		cinfo->after_ctime_nsec = fhp->fh_post_attr.ctime.tv_nsec;
+	}
 }
 
 int nfs4svc_encode_voidres(struct svc_rqst *, __be32 *, void *);