fs: anon_inodes implement dname

Add a d_dname method for anon_inodes filesystem, the same way pipefs and
sockfs pseudo filesystems.  This allows us to remove the DCACHE_UNHASHED
hack from anon_inodes.c (see next patch).

[AV: inumber is useless here, dropped from anon_inodefs_dname()]
Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Miklos Szeredi <mszeredi@suse.cz>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/anon_inodes.c

@@ -45,6 +45,15 @@ static int anon_inodefs_delete_dentry(struct dentry *dentry)
 	return 1;
 }
 
+/*
+ * anon_inodefs_dname() is called from d_path().
+ */
+static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
+{
+	return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
+				dentry->d_name.name);
+}
+
 static struct file_system_type anon_inode_fs_type = {
 	.name		= "anon_inodefs",
 	.get_sb		= anon_inodefs_get_sb,
@@ -52,6 +61,7 @@ static struct file_system_type anon_inode_fs_type = {
 };
 static const struct dentry_operations anon_inodefs_dentry_operations = {
 	.d_delete	= anon_inodefs_delete_dentry,
+	.d_dname	= anon_inodefs_dname,
 };
 
 /*