NFS: Optimise away unnecessary setattrs for open(O_TRUNC);

Currently, we will correctly optimise away a truncate that doesn't
change the file size. However, in the case of open(O_TRUNC), we
also want to optimise away the time changes.

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

fs/nfs/dir.c

@@ -1429,6 +1429,7 @@ static struct dentry *nfs_atomic_lookup(struct inode *dir, struct dentry *dentry
 	}
 
 	open_flags = nd->intent.open.flags;
+	attr.ia_valid = 0;
 
 	ctx = create_nfs_open_context(dentry, open_flags);
 	res = ERR_CAST(ctx);
@@ -1437,11 +1438,14 @@ static struct dentry *nfs_atomic_lookup(struct inode *dir, struct dentry *dentry
 
 	if (nd->flags & LOOKUP_CREATE) {
 		attr.ia_mode = nd->intent.open.create_mode;
-		attr.ia_valid = ATTR_MODE;
+		attr.ia_valid |= ATTR_MODE;
 		attr.ia_mode &= ~current_umask();
-	} else {
+	} else
 		open_flags &= ~(O_EXCL | O_CREAT);
-		attr.ia_valid = 0;
+
+	if (open_flags & O_TRUNC) {
+		attr.ia_valid |= ATTR_SIZE;
+		attr.ia_size = 0;
 	}
 
 	/* Open the file on the server */
@@ -1495,6 +1499,7 @@ static int nfs_open_revalidate(struct dentry *dentry, struct nameidata *nd)
 	struct inode *inode;
 	struct inode *dir;
 	struct nfs_open_context *ctx;
+	struct iattr attr;
 	int openflags, ret = 0;
 
 	if (nd->flags & LOOKUP_RCU)
@@ -1523,19 +1528,27 @@ static int nfs_open_revalidate(struct dentry *dentry, struct nameidata *nd)
 	/* We cannot do exclusive creation on a positive dentry */
 	if ((openflags & (O_CREAT|O_EXCL)) == (O_CREAT|O_EXCL))
 		goto no_open_dput;
-	/* We can't create new files, or truncate existing ones here */
-	openflags &= ~(O_CREAT|O_EXCL|O_TRUNC);
+	/* We can't create new files here */
+	openflags &= ~(O_CREAT|O_EXCL);
 
 	ctx = create_nfs_open_context(dentry, openflags);
 	ret = PTR_ERR(ctx);
 	if (IS_ERR(ctx))
 		goto out;
+
+	attr.ia_valid = 0;
+	if (openflags & O_TRUNC) {
+		attr.ia_valid |= ATTR_SIZE;
+		attr.ia_size = 0;
+		nfs_wb_all(inode);
+	}
+
 	/*
 	 * Note: we're not holding inode->i_mutex and so may be racing with
 	 * operations that change the directory. We therefore save the
 	 * change attribute *before* we do the RPC call.
 	 */
-	inode = NFS_PROTO(dir)->open_context(dir, ctx, openflags, NULL);
+	inode = NFS_PROTO(dir)->open_context(dir, ctx, openflags, &attr);
 	if (IS_ERR(inode)) {
 		ret = PTR_ERR(inode);
 		switch (ret) {

fs/nfs/inode.c

@@ -402,7 +402,7 @@ out_no_inode:
 	goto out;
 }
 
-#define NFS_VALID_ATTRS (ATTR_MODE|ATTR_UID|ATTR_GID|ATTR_SIZE|ATTR_ATIME|ATTR_ATIME_SET|ATTR_MTIME|ATTR_MTIME_SET|ATTR_FILE)
+#define NFS_VALID_ATTRS (ATTR_MODE|ATTR_UID|ATTR_GID|ATTR_SIZE|ATTR_ATIME|ATTR_ATIME_SET|ATTR_MTIME|ATTR_MTIME_SET|ATTR_FILE|ATTR_OPEN)
 
 int
 nfs_setattr(struct dentry *dentry, struct iattr *attr)
@@ -424,7 +424,7 @@ nfs_setattr(struct dentry *dentry, struct iattr *attr)
 
 	/* Optimization: if the end result is no change, don't RPC */
 	attr->ia_valid &= NFS_VALID_ATTRS;
-	if ((attr->ia_valid & ~ATTR_FILE) == 0)
+	if ((attr->ia_valid & ~(ATTR_FILE|ATTR_OPEN)) == 0)
 		return 0;
 
 	/* Write all dirty data */

fs/nfs/nfs4proc.c

@@ -828,7 +828,7 @@ static struct nfs4_opendata *nfs4_opendata_alloc(struct dentry *dentry,
 	p->o_arg.bitmask = server->attr_bitmask;
 	p->o_arg.dir_bitmask = server->cache_consistency_bitmask;
 	p->o_arg.claim = NFS4_OPEN_CLAIM_NULL;
-	if (flags & O_CREAT) {
+	if (attrs != NULL && attrs->ia_valid != 0) {
 		u32 *s;
 
 		p->o_arg.u.attrs = &p->attrs;
@@ -885,7 +885,7 @@ static int can_open_cached(struct nfs4_state *state, fmode_t mode, int open_mode
 {
 	int ret = 0;
 
-	if (open_mode & O_EXCL)
+	if (open_mode & (O_EXCL|O_TRUNC))
 		goto out;
 	switch (mode & (FMODE_READ|FMODE_WRITE)) {
 		case FMODE_READ:
@@ -1033,7 +1033,7 @@ static struct nfs4_state *nfs4_try_open_cached(struct nfs4_opendata *opendata)
 	struct nfs4_state *state = opendata->state;
 	struct nfs_inode *nfsi = NFS_I(state->inode);
 	struct nfs_delegation *delegation;
-	int open_mode = opendata->o_arg.open_flags & O_EXCL;
+	int open_mode = opendata->o_arg.open_flags & (O_EXCL|O_TRUNC);
 	fmode_t fmode = opendata->o_arg.fmode;
 	nfs4_stateid stateid;
 	int ret = -EAGAIN;
@@ -2431,6 +2431,10 @@ nfs4_proc_setattr(struct dentry *dentry, struct nfs_fattr *fattr,
 		}
 	}
 
+	/* Deal with open(O_TRUNC) */
+	if (sattr->ia_valid & ATTR_OPEN)
+		sattr->ia_valid &= ~(ATTR_MTIME|ATTR_CTIME|ATTR_OPEN);
+
 	status = nfs4_do_setattr(inode, cred, fattr, sattr, state);
 	if (status == 0)
 		nfs_setattr_update_inode(inode, sattr);