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>

1 files changed, 19 insertions, 6 deletions

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index fd9a872fada0..bb132a88f4e8 100644
--- a/fs/nfs/dir.c
+++ b/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) {