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>

1 files changed, 9 insertions, 3 deletions

diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
index e2e47ba..5a05559 100644
--- a/fs/ecryptfs/inode.c
+++ b/fs/ecryptfs/inode.c
@@ -674,10 +674,16 @@ out:
 	return rc ? ERR_PTR(rc) : buf;
 }
 
-static const char *ecryptfs_follow_link(struct dentry *dentry, void **cookie)
+static const char *ecryptfs_get_link(struct dentry *dentry,
+				     struct inode *inode, void **cookie)
 {
 	size_t len;
-	char *buf = ecryptfs_readlink_lower(dentry, &len);
+	char *buf;
+
+	if (!dentry)
+		return ERR_PTR(-ECHILD);
+
+	buf = ecryptfs_readlink_lower(dentry, &len);
 	if (IS_ERR(buf))
 		return buf;
 	fsstack_copy_attr_atime(d_inode(dentry),
@@ -1095,7 +1101,7 @@ out:
 
 const struct inode_operations ecryptfs_symlink_iops = {
 	.readlink = generic_readlink,
-	.follow_link = ecryptfs_follow_link,
+	.get_link = ecryptfs_get_link,
 	.put_link = kfree_put_link,
 	.permission = ecryptfs_permission,
 	.setattr = ecryptfs_setattr,