replace ->follow_link() with new method that could stay in RCU mode

new method: ->get_link(); replacement of ->follow_link().  The differences
are:
	* inode and dentry are passed separately
	* might be called both in RCU and non-RCU mode;
the former is indicated by passing it a NULL dentry.
	* when called that way it isn't allowed to block
and should return ERR_PTR(-ECHILD) if it needs to be called
in non-RCU mode.

It's a flagday change - the old method is gone, all in-tree instances
converted.  Conversion isn't hard; said that, so far very few instances
do not immediately bail out when called in RCU mode.  That'll change
in the next commits.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
index 063fdfc..1095056 100644
--- a/fs/gfs2/inode.c
+++ b/fs/gfs2/inode.c
@@ -1712,24 +1712,29 @@
 }
 
 /**
- * gfs2_follow_link - Follow a symbolic link
+ * gfs2_get_link - Follow a symbolic link
  * @dentry: The dentry of the link
- * @nd: Data that we pass to vfs_follow_link()
+ * @inode: The inode of the link
+ * @cookie: place to store the information for ->put_link()
  *
  * This can handle symlinks of any size.
  *
  * Returns: 0 on success or error code
  */
 
-static const char *gfs2_follow_link(struct dentry *dentry, void **cookie)
+static const char *gfs2_get_link(struct dentry *dentry,
+				 struct inode *inode, void **cookie)
 {
-	struct gfs2_inode *ip = GFS2_I(d_inode(dentry));
+	struct gfs2_inode *ip = GFS2_I(inode);
 	struct gfs2_holder i_gh;
 	struct buffer_head *dibh;
 	unsigned int size;
 	char *buf;
 	int error;
 
+	if (!dentry)
+		return ERR_PTR(-ECHILD);
+
 	gfs2_holder_init(ip->i_gl, LM_ST_SHARED, 0, &i_gh);
 	error = gfs2_glock_nq(&i_gh);
 	if (error) {
@@ -2132,7 +2137,7 @@
 
 const struct inode_operations gfs2_symlink_iops = {
 	.readlink = generic_readlink,
-	.follow_link = gfs2_follow_link,
+	.get_link = gfs2_get_link,
 	.put_link = kfree_put_link,
 	.permission = gfs2_permission,
 	.setattr = gfs2_setattr,