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

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Date:   Wed, 20 Dec 2017 09:37:31 +0200
From:   Serhey Popovych <serhe.popovych@...il.com>
To:     netdev@...r.kernel.org
Subject: [PATCH iproute2 3/3] utils: ll_map: Make network device name fixed size array of char

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@...il.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