[PATCH] too many setattr calls from VFS layer

[Chuck Lever]

new code in 2.5 VFS layer invokes notify_change to clear the suid and sgid
bits for every write request.  notify_change needs to optimize out calls
to ->setattr that don't do anything, because for many network file
systems, an on-the-wire SETATTR request is generated for every ->setattr
call, resulting in unnecessary latency for NFS writes.

diff -ruN 05-nfsroot/fs/attr.c 06-setattr/fs/attr.c
--- 05-nfsroot/fs/attr.c	Mon Nov  4 17:30:07 2002
+++ 06-setattr/fs/attr.c	Thu Nov  7 17:31:37 2002
@@ -134,6 +134,7 @@
 	if (!(ia_valid & ATTR_MTIME_SET))
 		attr->ia_mtime = now;
 	if (ia_valid & ATTR_KILL_SUID) {
+		attr->ia_valid &= ~ATTR_KILL_SUID;
 		if (mode & S_ISUID) {
 			if (!(ia_valid & ATTR_MODE)) {
 				ia_valid = attr->ia_valid |= ATTR_MODE;
@@ -143,6 +144,7 @@
 		}
 	}
 	if (ia_valid & ATTR_KILL_SGID) {
+		attr->ia_valid &= ~ ATTR_KILL_SGID;
 		if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
 			if (!(ia_valid & ATTR_MODE)) {
 				ia_valid = attr->ia_valid |= ATTR_MODE;
@@ -151,6 +153,8 @@
 			attr->ia_mode &= ~S_ISGID;
 		}
 	}
+	if (!attr->ia_valid)
+		return 0;
 
 	if (inode->i_op && inode->i_op->setattr) {
 		error = security_ops->inode_setattr(dentry, attr);