NFS: Allow optimisation of lseek(fd, SEEK_CUR, 0) on directories

There should be no need to grab the inode lock if we're only reading
the file offset.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 7a9c14426855309d2bb68e681b2db32321648d0c..8f8e9e9f2a790a8bb1f88928c4de7c4601cb0bcb 100644 (file)
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -904,23 +904,29 @@ static loff_t nfs_llseek_dir(struct file *filp, loff_t offset, int whence)
        dfprintk(FILE, "NFS: llseek dir(%pD2, %lld, %d)\n",
                        filp, offset, whence);
 
-       inode_lock(inode);
        switch (whence) {
-               case 1:
-                       offset += filp->f_pos;
-               case 0:
-                       if (offset >= 0)
-                               break;
-               default:
-                       offset = -EINVAL;
-                       goto out;
+       default:
+               return -EINVAL;
+       case SEEK_SET:
+               if (offset < 0)
+                       return -EINVAL;
+               inode_lock(inode);
+               break;
+       case SEEK_CUR:
+               if (offset == 0)
+                       return filp->f_pos;
+               inode_lock(inode);
+               offset += filp->f_pos;
+               if (offset < 0) {
+                       inode_unlock(inode);
+                       return -EINVAL;
+               }
        }
        if (offset != filp->f_pos) {
                filp->f_pos = offset;
                dir_ctx->dir_cookie = 0;
                dir_ctx->duped = 0;
        }
-out:
        inode_unlock(inode);
        return offset;
 }