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, 10 insertions, 8 deletions

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 1b4b9c5e51b7..235ad42afb57 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -140,12 +140,12 @@ struct ovl_link_data {
 	void *cookie;
 };
 
-static void *ovl_follow_link(struct dentry *dentry, struct nameidata *nd)
+static const char *ovl_follow_link(struct dentry *dentry, void **cookie, struct nameidata *nd)
 {
-	void *ret;
 	struct dentry *realdentry;
 	struct inode *realinode;
 	struct ovl_link_data *data = NULL;
+	const char *ret;
 
 	realdentry = ovl_dentry_real(dentry);
 	realinode = realdentry->d_inode;
@@ -160,19 +160,21 @@ static void *ovl_follow_link(struct dentry *dentry, struct nameidata *nd)
 		data->realdentry = realdentry;
 	}
 
-	ret = realinode->i_op->follow_link(realdentry, nd);
-	if (IS_ERR(ret)) {
+	ret = realinode->i_op->follow_link(realdentry, cookie, nd);
+	if (IS_ERR_OR_NULL(ret)) {
 		kfree(data);
 		return ret;
 	}
 
 	if (data)
-		data->cookie = ret;
+		data->cookie = *cookie;
 
-	return data;
+	*cookie = data;
+
+	return ret;
 }
 
-static void ovl_put_link(struct dentry *dentry, struct nameidata *nd, void *c)
+static void ovl_put_link(struct dentry *dentry, void *c)
 {
 	struct inode *realinode;
 	struct ovl_link_data *data = c;
@@ -181,7 +183,7 @@ static void ovl_put_link(struct dentry *dentry, struct nameidata *nd, void *c)
 		return;
 
 	realinode = data->realdentry->d_inode;
-	realinode->i_op->put_link(data->realdentry, nd, data->cookie);
+	realinode->i_op->put_link(data->realdentry, data->cookie);
 	kfree(data);
 }