NFS: Set meaningful value for fattr->time_start in readdirplus results.

Don't use uninitialsed value for fattr->time_start in readdirplus results.

The 'fattr' structure filled in by nfs3_decode_direct does not get a
value for ->time_start set.
Thus if an entry is for an inode that we already have in cache,
when nfs_readdir_lookup calls nfs_fhget, it will call nfs_refresh_inode
and may update the inode with out-of-date information.

Directories are read a page at a time, so each page could have a
different timestamp that "should" be used to set the time_start for
the fattr for info in that page.  However storing the timestamp per
page is awkward.  (We could stick in the first 4 bytes and only read 4092
bytes, but that is a bigger code change than I am interested it).

This patch ignores the readdir_plus attributes if a readdir finds the
information already in cache, and otherwise sets ->time_start to the time
the readdir request was sent to the server.

It might be nice to store - in the directory inode - the time stamp for
the earliest readdir request that is still in the page cache, so that we
don't ignore attribute data that we don't have to.  This patch doesn't do
that.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/dir.c

@@ -154,6 +154,8 @@ typedef struct {
 	decode_dirent_t	decode;
 	int		plus;
 	int		error;
+	unsigned long	timestamp;
+	int		timestamp_valid;
 } nfs_readdir_descriptor_t;
 
 /* Now we cache directories properly, by stuffing the dirent
@@ -195,6 +197,8 @@ int nfs_readdir_filler(nfs_readdir_descriptor_t *desc, struct page *page)
 		}
 		goto error;
 	}
+	desc->timestamp = timestamp;
+	desc->timestamp_valid = 1;
 	SetPageUptodate(page);
 	spin_lock(&inode->i_lock);
 	NFS_I(inode)->cache_validity |= NFS_INO_INVALID_ATIME;
@@ -225,6 +229,10 @@ int dir_decode(nfs_readdir_descriptor_t *desc)
 	if (IS_ERR(p))
 		return PTR_ERR(p);
 	desc->ptr = p;
+	if (desc->timestamp_valid)
+		desc->entry->fattr->time_start = desc->timestamp;
+	else
+		desc->entry->fattr->valid &= ~NFS_ATTR_FATTR;
 	return 0;
 }
 
@@ -316,6 +324,10 @@ int find_dirent_page(nfs_readdir_descriptor_t *desc)
 			__FUNCTION__, desc->page_index,
 			(long long) *desc->dir_cookie);
 
+	/* If we find the page in the page_cache, we cannot be sure
+	 * how fresh the data is, so we will ignore readdir_plus attributes.
+	 */
+	desc->timestamp_valid = 0;
 	page = read_cache_page(inode->i_mapping, desc->page_index,
 			       (filler_t *)nfs_readdir_filler, desc);
 	if (IS_ERR(page)) {
@@ -468,6 +480,7 @@ int uncached_readdir(nfs_readdir_descriptor_t *desc, void *dirent,
 	struct rpc_cred	*cred = nfs_file_cred(file);
 	struct page	*page = NULL;
 	int		status;
+	unsigned long	timestamp;
 
 	dfprintk(DIRCACHE, "NFS: uncached_readdir() searching for cookie %Lu\n",
 			(unsigned long long)*desc->dir_cookie);
@@ -477,6 +490,7 @@ int uncached_readdir(nfs_readdir_descriptor_t *desc, void *dirent,
 		status = -ENOMEM;
 		goto out;
 	}
+	timestamp = jiffies;
 	desc->error = NFS_PROTO(inode)->readdir(file->f_path.dentry, cred, *desc->dir_cookie,
 						page,
 						NFS_SERVER(inode)->dtsize,
@@ -487,6 +501,8 @@ int uncached_readdir(nfs_readdir_descriptor_t *desc, void *dirent,
 	desc->page = page;
 	desc->ptr = kmap(page);		/* matching kunmap in nfs_do_filldir */
 	if (desc->error >= 0) {
+		desc->timestamp = timestamp;
+		desc->timestamp_valid = 1;
 		if ((status = dir_decode(desc)) == 0)
 			desc->entry->prev_cookie = *desc->dir_cookie;
 	} else