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, 8 insertions, 4 deletions

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 4060ffde8722..38a0b8b9f8b9 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -137,17 +137,21 @@ struct ovl_link_data {
         void *cookie;
 };
 
-static const char *ovl_follow_link(struct dentry *dentry, void **cookie)
+static const char *ovl_get_link(struct dentry *dentry,
+                                struct inode *inode, void **cookie)
 {
         struct dentry *realdentry;
         struct inode *realinode;
         struct ovl_link_data *data = NULL;
         const char *ret;
 
+        if (!dentry)
+                return ERR_PTR(-ECHILD);
+
         realdentry = ovl_dentry_real(dentry);
         realinode = realdentry->d_inode;
 
-        if (WARN_ON(!realinode->i_op->follow_link))
+        if (WARN_ON(!realinode->i_op->get_link))
                 return ERR_PTR(-EPERM);
 
         if (realinode->i_op->put_link) {
@@ -157,7 +161,7 @@ static const char *ovl_follow_link(struct dentry *dentry, void **cookie)
                 data->realdentry = realdentry;
         }
 
-        ret = realinode->i_op->follow_link(realdentry, cookie);
+        ret = realinode->i_op->get_link(realdentry, realinode, cookie);
         if (IS_ERR_OR_NULL(ret)) {
                 kfree(data);
                 return ret;
@@ -378,7 +382,7 @@ static const struct inode_operations ovl_file_inode_operations = {
 
 static const struct inode_operations ovl_symlink_inode_operations = {
         .setattr        = ovl_setattr,
-        .follow_link    = ovl_follow_link,
+        .get_link       = ovl_get_link,
         .put_link       = ovl_put_link,
         .readlink       = ovl_readlink,
         .getattr        = ovl_getattr,