new ->follow_link() and ->put_link() calling conventions

a) instead of storing the symlink body (via nd_set_link()) and returning
an opaque pointer later passed to ->put_link(), ->follow_link() _stores_
that opaque pointer (into void * passed by address by caller) and returns
the symlink body.  Returning ERR_PTR() on error, NULL on jump (procfs magic
symlinks) and pointer to symlink body for normal symlinks.  Stored pointer
is ignored in all cases except the last one.

Storing NULL for opaque pointer (or not storing it at all) means no call
of ->put_link().

b) the body used to be passed to ->put_link() implicitly (via nameidata).
Now only the opaque pointer is.  In the cases when we used the symlink body
to free stuff, ->follow_link() now should store it as opaque pointer in addition
to returning it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 21 insertions, 45 deletions

diff --git a/fs/namei.c b/fs/namei.c
index ab2bcbdbd683..aeca44877371 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -502,7 +502,6 @@ struct nameidata {
 	int		last_type;
 	unsigned	depth;
 	struct file	*base;
-	char *saved_names[MAX_NESTED_LINKS + 1];
 };
 
 /*
@@ -713,23 +712,11 @@ void nd_jump_link(struct nameidata *nd, struct path *path)
 	nd->flags |= LOOKUP_JUMPED;
 }
 
-void nd_set_link(struct nameidata *nd, char *path)
-{
-	nd->saved_names[nd->depth] = path;
-}
-EXPORT_SYMBOL(nd_set_link);
-
-char *nd_get_link(struct nameidata *nd)
-{
-	return nd->saved_names[nd->depth];
-}
-EXPORT_SYMBOL(nd_get_link);
-
 static inline void put_link(struct nameidata *nd, struct path *link, void *cookie)
 {
 	struct inode *inode = link->dentry->d_inode;
-	if (inode->i_op->put_link)
-		inode->i_op->put_link(link->dentry, nd, cookie);
+	if (cookie && inode->i_op->put_link)
+		inode->i_op->put_link(link->dentry, cookie);
 	path_put(link);
 }
 
@@ -854,7 +841,7 @@ follow_link(struct path *link, struct nameidata *nd, void **p)
 {
 	struct dentry *dentry = link->dentry;
 	int error;
-	char *s;
+	const char *s;
 
 	BUG_ON(nd->flags & LOOKUP_RCU);
 
@@ -869,26 +856,20 @@ follow_link(struct path *link, struct nameidata *nd, void **p)
 	current->total_link_count++;
 
 	touch_atime(link);
-	nd_set_link(nd, NULL);
 
 	error = security_inode_follow_link(dentry);
 	if (error)
 		goto out_put_nd_path;
 
 	nd->last_type = LAST_BIND;
-	*p = dentry->d_inode->i_op->follow_link(dentry, nd);
-	error = PTR_ERR(*p);
-	if (IS_ERR(*p))
+	*p = NULL;
+	s = dentry->d_inode->i_op->follow_link(dentry, p, nd);
+	error = PTR_ERR(s);
+	if (IS_ERR(s))
 		goto out_put_nd_path;
 
 	error = 0;
-	s = nd_get_link(nd);
 	if (s) {
-		if (unlikely(IS_ERR(s))) {
-			path_put(&nd->path);
-			put_link(nd, link, *p);
-			return PTR_ERR(s);
-		}
 		if (*s == '/') {
 			if (!nd->root.mnt)
 				set_root(nd);
@@ -906,7 +887,6 @@ follow_link(struct path *link, struct nameidata *nd, void **p)
 	return error;
 
 out_put_nd_path:
-	*p = NULL;
 	path_put(&nd->path);
 	path_put(link);
 	return error;
@@ -4430,18 +4410,15 @@ EXPORT_SYMBOL(readlink_copy);
  */
 int generic_readlink(struct dentry *dentry, char __user *buffer, int buflen)
 {
-	struct nameidata nd;
 	void *cookie;
+	const char *link = dentry->d_inode->i_op->follow_link(dentry, &cookie, NULL);
 	int res;
 
-	nd.depth = 0;
-	cookie = dentry->d_inode->i_op->follow_link(dentry, &nd);
-	if (IS_ERR(cookie))
-		return PTR_ERR(cookie);
-
-	res = readlink_copy(buffer, buflen, nd_get_link(&nd));
-	if (dentry->d_inode->i_op->put_link)
-		dentry->d_inode->i_op->put_link(dentry, &nd, cookie);
+	if (IS_ERR(link))
+		return PTR_ERR(link);
+	res = readlink_copy(buffer, buflen, link);
+	if (cookie && dentry->d_inode->i_op->put_link)
+		dentry->d_inode->i_op->put_link(dentry, cookie);
 	return res;
 }
 EXPORT_SYMBOL(generic_readlink);
@@ -4473,22 +4450,21 @@ int page_readlink(struct dentry *dentry, char __user *buffer, int buflen)
 }
 EXPORT_SYMBOL(page_readlink);
 
-void *page_follow_link_light(struct dentry *dentry, struct nameidata *nd)
+const char *page_follow_link_light(struct dentry *dentry, void **cookie, struct nameidata *nd)
 {
 	struct page *page = NULL;
-	nd_set_link(nd, page_getlink(dentry, &page));
-	return page;
+	char *res = page_getlink(dentry, &page);
+	if (!IS_ERR(res))
+		*cookie = page;
+	return res;
 }
 EXPORT_SYMBOL(page_follow_link_light);
 
-void page_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
+void page_put_link(struct dentry *dentry, void *cookie)
 {
 	struct page *page = cookie;
-
-	if (page) {
-		kunmap(page);
-		page_cache_release(page);
-	}
+	kunmap(page);
+	page_cache_release(page);
 }
 EXPORT_SYMBOL(page_put_link);