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, 6 insertions, 3 deletions

diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
index f6e8354b8cea..63861c15e109 100644
--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -30,14 +30,17 @@ static const struct proc_ns_operations *ns_entries[] = {
 	&mntns_operations,
 };
 
-static const char *proc_ns_follow_link(struct dentry *dentry, void **cookie)
+static const char *proc_ns_get_link(struct dentry *dentry,
+				    struct inode *inode, void **cookie)
 {
-	struct inode *inode = d_inode(dentry);
 	const struct proc_ns_operations *ns_ops = PROC_I(inode)->ns_ops;
 	struct task_struct *task;
 	struct path ns_path;
 	void *error = ERR_PTR(-EACCES);
 
+	if (!dentry)
+		return ERR_PTR(-ECHILD);
+
 	task = get_proc_task(inode);
 	if (!task)
 		return error;
@@ -74,7 +77,7 @@ static int proc_ns_readlink(struct dentry *dentry, char __user *buffer, int bufl
 
 static const struct inode_operations proc_ns_link_inode_operations = {
 	.readlink	= proc_ns_readlink,
-	.follow_link	= proc_ns_follow_link,
+	.get_link	= proc_ns_get_link,
 	.setattr	= proc_setattr,
 };