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

[Serhey Popovych]

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.popov...@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