Add a general netlink socket parser

Introduce a general socket netlink parser which prints the header and
a string for the remaining part of the buffer.  It doesn't handle all
the netlink flags and types yet because the parser needs more
information, this will be implemented later.

* net.c (decode_sockbuf): New function.
(SYS_FUNC(send), SYS_FUNC(sendto), SYS_FUNC(recv), SYS_FUNC(recvfrom)):
Use it instead of printstr.
* msghdr.c (print_msghdr): Pass IOV_DECODE_NETLINK to tprint_iov_upto()
for netlink sockets.
* netlink.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* defs.h (decode_netlink, getfdproto): New prototypes.
(iov_decode): Add IOV_DECODER_NETLINK.
* io.c (print_iovec): Use decode_netlink().
* util.c (getfdproto): Remove static keyword.
* xlat/netlink_flags.in: New file.
* xlat/netlink_types.in: New file.
diff --git a/netlink.c b/netlink.c
new file mode 100644
index 0000000..c43f6e7
--- /dev/null
+++ b/netlink.c
@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2016 Fabien Siron <fabien.siron@epita.fr>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "defs.h"
+#include <sys/socket.h>
+#include <linux/netlink.h>
+#include "xlat/netlink_flags.h"
+#include "xlat/netlink_types.h"
+
+void
+decode_netlink(struct tcb *tcp, unsigned long addr, unsigned long size)
+{
+	struct nlmsghdr nlmsghdr;
+
+	if (size < sizeof(struct nlmsghdr)) {
+		printstr(tcp, addr, size);
+		return;
+	}
+	if (umove_or_printaddr(tcp, addr, &nlmsghdr))
+		return;
+
+	tprintf("{{len=%u, type=", nlmsghdr.nlmsg_len);
+
+	printxval(netlink_types, nlmsghdr.nlmsg_type, "NLMSG_???");
+
+	tprints(", flags=");
+	printflags(netlink_flags, nlmsghdr.nlmsg_flags, "NLM_F_???");
+	/* manage get/new requests */
+
+	tprintf(", seq=%u, pid=%u}", nlmsghdr.nlmsg_seq,
+		nlmsghdr.nlmsg_pid);
+
+	if (size - sizeof(struct nlmsghdr) > 0) {
+		tprints(", ");
+		printstr(tcp, addr + sizeof(struct nlmsghdr),
+			 size - sizeof(struct nlmsghdr));
+	}
+
+	tprints("}");
+}