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/self.c b/fs/proc/self.c
index 113b8d0..9dd0ae6 100644
--- a/fs/proc/self.c
+++ b/fs/proc/self.c
@@ -18,12 +18,15 @@ static int proc_self_readlink(struct dentry *dentry, char __user *buffer,
 	return readlink_copy(buffer, buflen, tmp);
 }
 
-static const char *proc_self_follow_link(struct dentry *dentry, void **cookie)
+static const char *proc_self_get_link(struct dentry *dentry,
+				      struct inode *inode, void **cookie)
 {
-	struct pid_namespace *ns = dentry->d_sb->s_fs_info;
+	struct pid_namespace *ns = inode->i_sb->s_fs_info;
 	pid_t tgid = task_tgid_nr_ns(current, ns);
 	char *name;
 
+	if (!dentry)
+		return ERR_PTR(-ECHILD);
 	if (!tgid)
 		return ERR_PTR(-ENOENT);
 	/* 11 for max length of signed int in decimal + NULL term */
@@ -36,7 +39,7 @@ static const char *proc_self_follow_link(struct dentry *dentry, void **cookie)
 
 static const struct inode_operations proc_self_inode_operations = {
 	.readlink	= proc_self_readlink,
-	.follow_link	= proc_self_follow_link,
+	.get_link	= proc_self_get_link,
 	.put_link	= kfree_put_link,
 };