[PATCH] NFS: Ensure that we revalidate the cached file length for llseek(SEEK_END)

This fixes a data corruption error for mail delivery applications that
expect to be able to do posix locking and then append writes on NFS.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index f06eee6..55c9075 100644 (file)
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -37,6 +37,7 @@
 
 static int nfs_file_open(struct inode *, struct file *);
 static int nfs_file_release(struct inode *, struct file *);
+static loff_t nfs_file_llseek(struct file *file, loff_t offset, int origin);
 static int  nfs_file_mmap(struct file *, struct vm_area_struct *);
 static ssize_t nfs_file_sendfile(struct file *, loff_t *, size_t, read_actor_t, void *);
 static ssize_t nfs_file_read(struct kiocb *, char __user *, size_t, loff_t);
@@ -48,7 +49,7 @@ static int nfs_lock(struct file *filp, int cmd, struct file_lock *fl);
 static int nfs_flock(struct file *filp, int cmd, struct file_lock *fl);
 
 struct file_operations nfs_file_operations = {
-       .llseek         = remote_llseek,
+       .llseek         = nfs_file_llseek,
        .read           = do_sync_read,
        .write          = do_sync_write,
        .aio_read               = nfs_file_read,
@@ -114,6 +115,45 @@ nfs_file_release(struct inode *inode, struct file *filp)
        return NFS_PROTO(inode)->file_release(inode, filp);
 }
 
+/**
+ * nfs_revalidate_size - Revalidate the file size
+ * @inode - pointer to inode struct
+ * @file - pointer to struct file
+ *
+ * Revalidates the file length. This is basically a wrapper around
+ * nfs_revalidate_inode() that takes into account the fact that we may
+ * have cached writes (in which case we don't care about the server's
+ * idea of what the file length is), or O_DIRECT (in which case we
+ * shouldn't trust the cache).
+ */
+static int nfs_revalidate_file_size(struct inode *inode, struct file *filp)
+{
+       struct nfs_server *server = NFS_SERVER(inode);
+       struct nfs_inode *nfsi = NFS_I(inode);
+
+       if (server->flags & NFS_MOUNT_NOAC)
+               goto force_reval;
+       if (filp->f_flags & O_DIRECT)
+               goto force_reval;
+       if (nfsi->npages != 0)
+               return 0;
+       return nfs_revalidate_inode(server, inode);
+force_reval:
+       return __nfs_revalidate_inode(server, inode);
+}
+
+static loff_t nfs_file_llseek(struct file *filp, loff_t offset, int origin)
+{
+       /* origin == SEEK_END => we must revalidate the cached file length */
+       if (origin == 2) {
+               struct inode *inode = filp->f_mapping->host;
+               int retval = nfs_revalidate_file_size(inode, filp);
+               if (retval < 0)
+                       return (loff_t)retval;
+       }
+       return remote_llseek(filp, offset, origin);
+}
+
 /*
  * Flush all dirty pages, and check for write errors.
  *