syscall() example

c/sysctl_ex/_sysctl_ex.c

@@ -0,0 +1,63 @@
+#define _GNU_SOURCE
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <linux/sysctl.h>
+#include <errno.h>
+
+int _sysctl(struct __sysctl_args *args );
+
+#define OSNAMESZ 100
+void test0_osname()
+{
+    struct __sysctl_args args;
+    char osname[OSNAMESZ];
+    size_t osnamelth;
+    int name[] = { CTL_KERN, KERN_OSTYPE };
+
+    memset(&args, 0, sizeof(struct __sysctl_args));
+    args.name = name;
+    args.nlen = sizeof(name)/sizeof(name[0]);
+    args.oldval = osname;
+    args.oldlenp = &osnamelth;
+
+    osnamelth = sizeof(osname);
+
+    if (syscall(SYS__sysctl, &args) == -1) {
+        perror("_sysctl");
+        exit(EXIT_FAILURE);
+    }
+    printf("This machine is running %*s\n", (int)osnamelth, osname);
+}
+
+void test1_tcp_max_syn_backlog()
+{
+    struct __sysctl_args args;
+    int var;
+    size_t var_len;
+    int name[] = { CTL_NET, NET_IPV4, NET_TCP_MAX_SYN_BACKLOG };
+
+    memset(&args, 0, sizeof(struct __sysctl_args));
+    args.name = name;
+    args.nlen = sizeof(name)/sizeof(name[0]);
+    args.oldval = &var;
+    args.oldlenp = &var_len;
+
+    if (syscall(SYS__sysctl, &args) == -1) {
+        perror("_sysctl");
+        exit(EXIT_FAILURE);
+    }
+    printf("NET_TCP_MAX_SYN_BACKLOG = %u\n", var);
+}
+
+int
+main(void)
+{
+	test0_osname();
+
+	test1_tcp_max_syn_backlog();
+
+	exit(EXIT_SUCCESS);
+}