Subject: Re: [PATCH 2/2] iproute: Add route showdump command (v2)

From: Pavel Emelyanov <[email-masked]>
Date: Fri, 27 Jul 2012 10:06:15 +0400

On 07/27/2012 09:03 AM, Pavel Emelyanov wrote:
> As you know, the save/restore pair for routes works in a very simple and
> elegant manner -- on save the raw kernel rtnl stream is just put into a
> file, on restore the _very_ _same_ messages are pushed back to the kernel.
> 
> Is the same trick possible to save and restore the addresses (the ip
> addr command) as well? Or the RTM_GETADDR messages cannot be just read
> from and written back to the network stack in a generic case?

I mean something like the below, just put the RTM_GETADDR stream into a
file and push it back into the kernel as is. It worked for me in trivial
cases, but is this approach correct generically?

Log:

iproute: Add ability to save, restore and show the interfaces' addresses

Implementation is similar to the ip route {save|restore|showdump} one.

Signed-off-by: Pavel Emelyanov <[email-masked]>

---

diff --git a/ip/ipaddress.c b/ip/ipaddress.c
index 37deda5..6788544 100644
--- a/ip/ipaddress.c
+++ b/ip/ipaddress.c
@@ -34,6 +34,11 @@
 #include "ll_map.h"
 #include "ip_common.h"
 
+enum {
+	IPADD_LIST,
+	IPADD_FLUSH,
+	IPADD_SAVE,
+};
 
 static struct
 {
@@ -65,8 +70,9 @@ static void usage(void)
 	fprintf(stderr, "Usage: ip addr {add|change|replace} IFADDR dev STRING [ LIFETIME ]\n");
 	fprintf(stderr, "                                                      [ CONFFLAG-LIST ]\n");
 	fprintf(stderr, "       ip addr del IFADDR dev STRING\n");
-	fprintf(stderr, "       ip addr {show|flush} [ dev STRING ] [ scope SCOPE-ID ]\n");
+	fprintf(stderr, "       ip addr {show|save|flush} [ dev STRING ] [ scope SCOPE-ID ]\n");
 	fprintf(stderr, "                            [ to PREFIX ] [ FLAG-LIST ] [ label PATTERN ]\n");
+	fprintf(stderr, "       ip addr {showdump|restore}\n");
 	fprintf(stderr, "IFADDR := PREFIX | ADDR peer PREFIX\n");
 	fprintf(stderr, "          [ broadcast ADDR ] [ anycast ADDR ]\n");
 	fprintf(stderr, "          [ label STRING ] [ scope SCOPE-ID ]\n");
@@ -768,6 +774,99 @@ static int store_nlmsg(const struct sockaddr_nl *who, struct nlmsghdr *n,
 	return 0;
 }
 
+static __u32 ipadd_dump_magic = 0x47361222;
+
+static int ipadd_save_prep(void)
+{
+	int ret;
+
+	if (isatty(STDOUT_FILENO)) {
+		fprintf(stderr, "Not sending binary stream to stdout\n");
+		return -1;
+	}
+
+	ret = write(STDOUT_FILENO, &ipadd_dump_magic, sizeof(ipadd_dump_magic));
+	if (ret != sizeof(ipadd_dump_magic)) {
+		fprintf(stderr, "Can't write magic to dump file\n");
+		return -1;
+	}
+
+	return 0;
+}
+
+static int ipadd_dump_check_magic(void)
+{
+	int ret;
+	__u32 magic = 0;
+
+	if (isatty(STDIN_FILENO)) {
+		fprintf(stderr, "Can't restore addr dump from a terminal\n");
+		return -1;
+	}
+
+	ret = fread(&magic, sizeof(magic), 1, stdin);
+	if (magic != ipadd_dump_magic) {
+		fprintf(stderr, "Magic mismatch (%d elems, %x magic)\n", ret, magic);
+		return -1;
+	}
+
+	return 0;
+}
+
+static int save_nlmsg(const struct sockaddr_nl *who, struct nlmsghdr *n,
+		       void *arg)
+{
+	int ret;
+
+	ret = write(STDOUT_FILENO, n, n->nlmsg_len);
+	if ((ret > 0) && (ret != n->nlmsg_len)) {
+		fprintf(stderr, "Short write while saving nlmsg\n");
+		ret = -EIO;
+	}
+
+	return ret == n->nlmsg_len ? 0 : ret;
+}
+
+static int show_handler(const struct sockaddr_nl *nl, struct nlmsghdr *n, void *arg)
+{
+	struct ifaddrmsg *ifa = NLMSG_DATA(n);
+
+	printf("if%d:\n", ifa->ifa_index);
+	print_addrinfo(NULL, n, stdout);
+	return 0;
+}
+
+static int ipaddr_showdump(void)
+{
+	if (ipadd_dump_check_magic())
+		exit(-1);
+
+	exit(rtnl_from_file(stdin, &show_handler, NULL));
+}
+
+static int restore_handler(const struct sockaddr_nl *nl, struct nlmsghdr *n, void *arg)
+{
+	int ret;
+
+	n->nlmsg_flags |= NLM_F_REQUEST | NLM_F_CREATE | NLM_F_ACK;
+
+	ll_init_map(&rth);
+
+	ret = rtnl_talk(&rth, n, 0, 0, n);
+	if ((ret < 0) && (errno == EEXIST))
+		ret = 0;
+
+	return ret;
+}
+
+static int ipaddr_restore(void)
+{
+	if (ipadd_dump_check_magic())
+		exit(-1);
+
+	exit(rtnl_from_file(stdin, &restore_handler, NULL));
+}
+
 static void free_nlmsg_chain(struct nlmsg_chain *info)
 {
 	struct nlmsg_list *l, *n;
@@ -902,7 +1001,7 @@ static int ipaddr_flush(void)
 	return 1;
 }
 
-static int ipaddr_list_or_flush(int argc, char **argv, int flush)
+static int ipaddr_list_flush_or_save(int argc, char **argv, int action)
 {
 	struct nlmsg_chain linfo = { NULL, NULL};
 	struct nlmsg_chain ainfo = { NULL, NULL};
@@ -918,7 +1017,7 @@ static int ipaddr_list_or_flush(int argc, char **argv, int flush)
 
 	filter.group = INIT_NETDEV_GROUP;
 
-	if (flush) {
+	if (action == IPADD_FLUSH) {
 		if (argc <= 0) {
 			fprintf(stderr, "Flush requires arguments.\n");
 
@@ -1005,9 +1104,26 @@ static int ipaddr_list_or_flush(int argc, char **argv, int flush)
 		}
 	}
 
-	if (flush)
+	if (action == IPADD_FLUSH)
 		return ipaddr_flush();
 
+	if (action == IPADD_SAVE) {
+		if (ipadd_save_prep())
+			exit(1);
+
+		if (rtnl_wilddump_request(&rth, preferred_family, RTM_GETADDR) < 0) {
+			perror("Cannot send dump request");
+			exit(1);
+		}
+
+		if (rtnl_dump_filter(&rth, save_nlmsg, stdout) < 0) {
+			fprintf(stderr, "Save terminated\n");
+			exit(1);
+		}
+
+		exit(0);
+	}
+
 	if (rtnl_wilddump_request(&rth, preferred_family, RTM_GETLINK) < 0) {
 		perror("Cannot send dump request");
 		exit(1);
@@ -1055,7 +1171,7 @@ int ipaddr_list_link(int argc, char **argv)
 {
 	preferred_family = AF_PACKET;
 	do_link = 1;
-	return ipaddr_list_or_flush(argc, argv, 0);
+	return ipaddr_list_flush_or_save(argc, argv, IPADD_LIST);
 }
 
 void ipaddr_reset_filter(int oneline)
@@ -1271,7 +1387,7 @@ static int ipaddr_modify(int cmd, int flags, int argc, char **argv)
 int do_ipaddr(int argc, char **argv)
 {
 	if (argc < 1)
-		return ipaddr_list_or_flush(0, NULL, 0);
+		return ipaddr_list_flush_or_save(0, NULL, IPADD_LIST);
 	if (matches(*argv, "add") == 0)
 		return ipaddr_modify(RTM_NEWADDR, NLM_F_CREATE|NLM_F_EXCL, argc-1, argv+1);
 	if (matches(*argv, "change") == 0 ||
@@ -1283,9 +1399,15 @@ int do_ipaddr(int argc, char **argv)
 		return ipaddr_modify(RTM_DELADDR, 0, argc-1, argv+1);
 	if (matches(*argv, "list") == 0 || matches(*argv, "show") == 0
 	    || matches(*argv, "lst") == 0)
-		return ipaddr_list_or_flush(argc-1, argv+1, 0);
+		return ipaddr_list_flush_or_save(argc-1, argv+1, IPADD_LIST);
 	if (matches(*argv, "flush") == 0)
-		return ipaddr_list_or_flush(argc-1, argv+1, 1);
+		return ipaddr_list_flush_or_save(argc-1, argv+1, IPADD_FLUSH);
+	if (matches(*argv, "save") == 0)
+		return ipaddr_list_flush_or_save(argc-1, argv+1, IPADD_SAVE);
+	if (matches(*argv, "showdump") == 0)
+		return ipaddr_showdump();
+	if (matches(*argv, "restore") == 0)
+		return ipaddr_restore();
 	if (matches(*argv, "help") == 0)
 		usage();
 	fprintf(stderr, "Command \"%s\" is unknown, try \"ip addr help\".\n", *argv);