[PATCH iproute2 3/3] utils: ll_map: Make network device name fixed size array of char

[Serhey Popovych <serhe.popovych@gmail.com>]

Network device names are fixed in size and never exceed
IFNAMSIZ (16 bytes).

Make name fixed size array to always malloc() same size chunk
of memory and use memcpy()/memcmp() with constant IFNAMSIZ
to benefit from possible compiler optimizations replacing
call to a function with two/four load/store instructions
on 64/32 bit systems.

Check if IFLA_IFNAME attribute present in netlink message
(should always) and use strncpy() to pad name with zeros.

Signed-off-by: Serhey Popovych <serhe.popovych@gmail.com>
---
 lib/ll_map.c |   20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/lib/ll_map.c b/lib/ll_map.c
index abe7bdc..fcbf0fb 100644
--- a/lib/ll_map.c
+++ b/lib/ll_map.c
@@ -30,7 +30,7 @@ struct ll_cache {
 	unsigned	flags;
 	unsigned 	index;
 	unsigned short	type;
-	char		name[];
+	char		name[IFNAMSIZ];
 };
 
 #define IDXMAP_SIZE	1024
@@ -71,7 +71,7 @@ static struct ll_cache *ll_get_by_name(const char *name)
 		struct ll_cache *im
 			= container_of(n, struct ll_cache, name_hash);
 
-		if (strncmp(im->name, name, IFNAMSIZ) == 0)
+		if (!strcmp(im->name, name))
 			return im;
 	}
 
@@ -82,7 +82,7 @@ int ll_remember_index(const struct sockaddr_nl *who,
 		      struct nlmsghdr *n, void *arg)
 {
 	unsigned int h;
-	const char *ifname;
+	char ifname[IFNAMSIZ];
 	struct ifinfomsg *ifi = NLMSG_DATA(n);
 	struct ll_cache *im;
 	struct rtattr *tb[IFLA_MAX+1];
@@ -105,17 +105,21 @@ int ll_remember_index(const struct sockaddr_nl *who,
 	}
 
 	parse_rtattr(tb, IFLA_MAX, IFLA_RTA(ifi), IFLA_PAYLOAD(n));
-	ifname = rta_getattr_str(tb[IFLA_IFNAME]);
-	if (ifname == NULL)
+
+	if (!tb[IFLA_IFNAME])
+		return 0;
+	strncpy(ifname, rta_getattr_str(tb[IFLA_IFNAME]), IFNAMSIZ);
+	if (!ifname[0])
 		return 0;
+	ifname[IFNAMSIZ - 1] = '\0';
 
 	if (im) {
 		/* change to existing entry */
-		rehash = strcmp(im->name, ifname);
+		rehash = memcmp(im->name, ifname, IFNAMSIZ);
 		if (rehash)
 			hlist_del(&im->name_hash);
 	} else {
-		im = malloc(sizeof(*im) + strlen(ifname) + 1);
+		im = malloc(sizeof(*im));
 		if (!im)
 			return 0;
 		im->index = ifi->ifi_index;
@@ -133,7 +137,7 @@ int ll_remember_index(const struct sockaddr_nl *who,
 		h = namehash(ifname) & (IDXMAP_SIZE - 1);
 		hlist_add_head(&im->name_hash, &name_head[h]);
 
-		strcpy(im->name, ifname);
+		memcpy(im->name, ifname, IFNAMSIZ);
 	}
 
 	return 0;
-- 
1.7.10.4