avoid __synccall for setrlimit on kernels with prlimit syscall

resource limits have been process-wide since linux 2.6.10, and the
prlimit syscall was added in 2.6.36, so prlimit can be assumed to set
the resource limits correctly for the whole process.

src/misc/setrlimit.c

@@ -6,25 +6,8 @@
 #define MIN(a, b) ((a)<(b) ? (a) : (b))
 #define FIX(x) do{ if ((x)>=SYSCALL_RLIM_INFINITY) (x)=RLIM_INFINITY; }while(0)
 
-static int __setrlimit(int resource, const struct rlimit *rlim)
-{
-	unsigned long k_rlim[2];
-	struct rlimit tmp;
-	if (SYSCALL_RLIM_INFINITY != RLIM_INFINITY) {
-		tmp = *rlim;
-		FIX(tmp.rlim_cur);
-		FIX(tmp.rlim_max);
-		rlim = &tmp;
-	}
-	int ret = __syscall(SYS_prlimit64, 0, resource, rlim, 0);
-	if (ret != -ENOSYS) return ret;
-	k_rlim[0] = MIN(rlim->rlim_cur, MIN(-1UL, SYSCALL_RLIM_INFINITY));
-	k_rlim[1] = MIN(rlim->rlim_max, MIN(-1UL, SYSCALL_RLIM_INFINITY));
-	return __syscall(SYS_setrlimit, resource, k_rlim);
-}
-
 struct ctx {
-	const struct rlimit *rlim;
+	unsigned long lim[2];
 	int res;
 	int err;
 };
@@ -33,12 +16,26 @@ static void do_setrlimit(void *p)
 {
 	struct ctx *c = p;
 	if (c->err>0) return;
-	c->err = -__setrlimit(c->res, c->rlim);
+	c->err = -__syscall(SYS_setrlimit, c->res, c->lim);
 }
 
 int setrlimit(int resource, const struct rlimit *rlim)
 {
-	struct ctx c = { .res = resource, .rlim = rlim, .err = -1 };
+	struct rlimit tmp;
+	if (SYSCALL_RLIM_INFINITY != RLIM_INFINITY) {
+		tmp = *rlim;
+		FIX(tmp.rlim_cur);
+		FIX(tmp.rlim_max);
+		rlim = &tmp;
+	}
+	int ret = __syscall(SYS_prlimit64, 0, resource, rlim, 0);
+	if (ret != -ENOSYS) return __syscall_ret(ret);
+
+	struct ctx c = {
+		.lim[0] = MIN(rlim->rlim_cur, MIN(-1UL, SYSCALL_RLIM_INFINITY)),
+		.lim[1] = MIN(rlim->rlim_max, MIN(-1UL, SYSCALL_RLIM_INFINITY)),
+		.res = resource, .err = -1
+	};
 	__synccall(do_setrlimit, &c);
 	if (c.err) {
 		if (c.err>0) errno = c.err;