Implement lookup_dcookie syscall decoding

* lookup_dcookie.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* linux/dummy.h (sys_lookup_dcookie): Remove stub alias.

Makefile.am

@@ -87,6 +87,7 @@ strace_SOURCES =	\
 	keyctl.c	\
 	ldt.c		\
 	link.c		\
+	lookup_dcookie.c \
 	loop.c		\
 	lseek.c		\
 	mem.c		\

linux/dummy.h

@@ -32,7 +32,6 @@
 #endif
 
 /* still unfinished */
-#define	sys_lookup_dcookie	printargs
 #define	sys_name_to_handle_at	printargs
 #define	sys_open_by_handle_at	printargs
 #define	sys_sysfs		printargs

lookup_dcookie.c

@@ -0,0 +1,22 @@
+#include "defs.h"
+
+SYS_FUNC(lookup_dcookie)
+{
+	if (entering(tcp))
+		return 0;
+
+	/* cookie */
+	int argn = printllval(tcp, "%llu", 0);
+	tprints(", ");
+
+	/* buffer */
+	if (syserror(tcp))
+		printaddr(tcp->u_arg[argn]);
+	else
+		printstr(tcp, tcp->u_arg[argn], tcp->u_rval);
+
+	/* len */
+	tprintf(", %lu", tcp->u_arg[argn + 1]);
+
+	return 0;
+}