CIFS: Implement follow_link for SMB2

that allows to access files through symlink created on a server.

Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/link.c

@@ -509,6 +509,7 @@ cifs_follow_link(struct dentry *direntry, struct nameidata *nd)
 	struct cifs_sb_info *cifs_sb = CIFS_SB(inode->i_sb);
 	struct tcon_link *tlink = NULL;
 	struct cifs_tcon *tcon;
+	struct TCP_Server_Info *server;
 
 	xid = get_xid();
 
@@ -519,25 +520,7 @@ cifs_follow_link(struct dentry *direntry, struct nameidata *nd)
 		goto out;
 	}
 	tcon = tlink_tcon(tlink);
-
-	/*
-	 * For now, we just handle symlinks with unix extensions enabled.
-	 * Eventually we should handle NTFS reparse points, and MacOS
-	 * symlink support. For instance...
-	 *
-	 * rc = CIFSSMBQueryReparseLinkInfo(...)
-	 *
-	 * For now, just return -EACCES when the server doesn't support posix
-	 * extensions. Note that we still allow querying symlinks when posix
-	 * extensions are manually disabled. We could disable these as well
-	 * but there doesn't seem to be any harm in allowing the client to
-	 * read them.
-	 */
-	if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MF_SYMLINKS) &&
-	    !cap_unix(tcon->ses)) {
-		rc = -EACCES;
-		goto out;
-	}
+	server = tcon->ses->server;
 
 	full_path = build_path_from_dentry(direntry);
 	if (!full_path)
@@ -559,6 +542,9 @@ cifs_follow_link(struct dentry *direntry, struct nameidata *nd)
 	if ((rc != 0) && cap_unix(tcon->ses))
 		rc = CIFSSMBUnixQuerySymLink(xid, tcon, full_path, &target_path,
 					     cifs_sb->local_nls);
+	else if (rc != 0 && server->ops->query_symlink)
+		rc = server->ops->query_symlink(xid, tcon, full_path,
+						&target_path, cifs_sb);
 
 	kfree(full_path);
 out: