*: remove check for errors on getsockaddr in cases we know they can't happen

libbb: make get_sock_lsa use only one getsockaddr syscall, not two

function                                             old     new   delta
get_sock_lsa                                          72     101     +29
do_iplink                                           1151    1137     -14
arping_main                                         1585    1569     -16
dolisten                                             789     755     -34
xrtnl_open                                           161      94     -67

1 files changed, 13 insertions, 8 deletions

diff --git a/libbb/xconnect.c b/libbb/xconnect.c
index 1b4f4f78a..f853e9593 100644
--- a/libbb/xconnect.c
+++ b/libbb/xconnect.c
@@ -37,16 +37,21 @@ int FAST_FUNC setsockopt_bindtodevice(int fd, const char *iface)
 
 len_and_sockaddr* FAST_FUNC get_sock_lsa(int fd)
 {
-        len_and_sockaddr *lsa;
-        socklen_t len = 0;
+        len_and_sockaddr lsa;
+        len_and_sockaddr *lsa_ptr;
 
-        /* Can be optimized to do only one getsockname() */
-        if (getsockname(fd, NULL, &len) != 0)
+        lsa.len = LSA_SIZEOF_SA;
+        if (getsockname(fd, &lsa.u.sa, &lsa.len) != 0)
                 return NULL;
-        lsa = xzalloc(LSA_LEN_SIZE + len);
-        lsa->len = len;
-        getsockname(fd, &lsa->u.sa, &lsa->len);
-        return lsa;
+
+        lsa_ptr = xzalloc(LSA_LEN_SIZE + lsa.len);
+        if (lsa.len > LSA_SIZEOF_SA) { /* rarely (if ever) happens */
+                lsa_ptr->len = lsa.len;
+                getsockname(fd, &lsa_ptr->u.sa, &lsa_ptr->len);
+        } else {
+                memcpy(lsa_ptr, &lsa, LSA_LEN_SIZE + lsa.len);
+        }
+        return lsa_ptr;
 }
 
 void FAST_FUNC xconnect(int s, const struct sockaddr *s_addr, socklen_t addrlen)