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>

3 files changed, 28 insertions, 11 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) {
diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 577ad5a72a24..65486e652943 100644
--- a/fs/nfs/inode.c
+++ b/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 */
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 88a8b6999b4f..360240cc1e9b 100644
--- a/fs/nfs/nfs4proc.c
+++ b/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);