[PATCH 3/3] nfs-utils: don't fdatasync the rmtab

[Ben Myers <bpm@sgi.com>]

If we're using the new caching interface the rmtab will be ignored by exportfs
so there is no need to fdatasync.  This improves mountd performance.
---
 support/nfs/cacheio.c |    5 ++---
 support/nfs/rmtab.c   |   23 ++++++++++++++++++-----
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/support/nfs/cacheio.c b/support/nfs/cacheio.c
index 6a6ed5a..bdf5d84 100644
--- a/support/nfs/cacheio.c
+++ b/support/nfs/cacheio.c
@@ -285,9 +285,8 @@ int readline(int fd, char **buf, int *lenp)
 int
 check_new_cache(void)
 {
-	struct stat stb;
-	return	(stat("/proc/fs/nfs/filehandle", &stb) == 0) ||
-		(stat("/proc/fs/nfsd/filehandle", &stb) == 0);
+	return	(access("/proc/fs/nfs/filehandle", F_OK) == 0) ||
+		(access("/proc/fs/nfsd/filehandle", F_OK) == 0);
 }	
 
 
diff --git a/support/nfs/rmtab.c b/support/nfs/rmtab.c
index 4cbd285..a28abf3 100644
--- a/support/nfs/rmtab.c
+++ b/support/nfs/rmtab.c
@@ -117,11 +117,24 @@ void
 fendrmtabent(FILE *fp)
 {
 	if (fp) {
-		/* If it was written to, we really want
-		 * to flush to disk before returning
-		 */
-		fflush(fp);
-		fdatasync(fileno(fp));
+		static int have_new_cache = -1;
+		if (have_new_cache == -1) /* check only once */
+			have_new_cache = check_new_cache();
+
+		if (!have_new_cache) {
+			/*
+			 * If we are using the old caching interface: exportfs
+			 * uses the rmtab to determine what should be exported,
+			 * so it is important that it be up-to-date.
+			 *
+			 * If we are using the new caching interface: the rmtab
+			 * is ignored by exportfs and the fdatasync only serves
+			 * to slow us down.
+			 */
+			fflush(fp);
+			fdatasync(fileno(fp));
+		}
+
 		fclose(fp);
 	}
 }