kernel/sys.c: improve code generation

utsname() is quite expensive to calculate.  Cache it in a local.

          text    data     bss     dec     hex filename
before:  11136     720      16   11872    2e60 kernel/sys.o
after:   11096     720      16   11832    2e38 kernel/sys.o

Acked-by: Vegard Nossum <vegard.nossum@gmail.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: "Serge E. Hallyn" <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sys.c

@@ -1349,9 +1349,10 @@ asmlinkage long sys_sethostname(char __user *name, int len)
 	down_write(&uts_sem);
 	errno = -EFAULT;
 	if (!copy_from_user(tmp, name, len)) {
-		memcpy(utsname()->nodename, tmp, len);
-		memset(utsname()->nodename + len, 0,
-			sizeof(utsname()->nodename) - len);
+		struct new_utsname *u = utsname();
+
+		memcpy(u->nodename, tmp, len);
+		memset(u->nodename + len, 0, sizeof(u->nodename) - len);
 		errno = 0;
 	}
 	up_write(&uts_sem);
@@ -1363,15 +1364,17 @@ asmlinkage long sys_sethostname(char __user *name, int len)
 asmlinkage long sys_gethostname(char __user *name, int len)
 {
 	int i, errno;
+	struct new_utsname *u;
 
 	if (len < 0)
 		return -EINVAL;
 	down_read(&uts_sem);
-	i = 1 + strlen(utsname()->nodename);
+	u = utsname();
+	i = 1 + strlen(u->nodename);
 	if (i > len)
 		i = len;
 	errno = 0;
-	if (copy_to_user(name, utsname()->nodename, i))
+	if (copy_to_user(name, u->nodename, i))
 		errno = -EFAULT;
 	up_read(&uts_sem);
 	return errno;
@@ -1396,9 +1399,10 @@ asmlinkage long sys_setdomainname(char __user *name, int len)
 	down_write(&uts_sem);
 	errno = -EFAULT;
 	if (!copy_from_user(tmp, name, len)) {
-		memcpy(utsname()->domainname, tmp, len);
-		memset(utsname()->domainname + len, 0,
-			sizeof(utsname()->domainname) - len);
+		struct new_utsname *u = utsname();
+
+		memcpy(u->domainname, tmp, len);
+		memset(u->domainname + len, 0, sizeof(u->domainname) - len);
 		errno = 0;
 	}
 	up_write(&uts_sem);