Add initial implementation of sysctl(8)

Needs a bit of cleanup (avoiding magic numbers etc.).

Makefile

@@ -47,6 +47,7 @@ SRC = \
 	swapoff.c           \
 	swapon.c            \
 	switch_root.c       \
+	sysctl.c            \
 	truncate.c          \
 	umount.c            \
 	unshare.c           \
@@ -92,6 +93,7 @@ MAN8 = \
 	swapoff.8           \
 	swapon.8            \
 	switch_root.8       \
+	sysctl.8            \
 	umount.8
 
 OBJ = $(SRC:.c=.o) $(LIB)

README

@@ -9,7 +9,7 @@ The following programs are currently implemented:
     chvt clear ctrlaltdel df dmesg  eject fallocate free getty halt id
     insmod killall5 lsmod lsusb mknod mkswap mount mountpoint pagesize
     pidof  pivot_root   ps  respawn  rmmod  stat   su  swapoff  swapon
-    switch_root truncate umount unshare uptime watch who
+    switch_root sysctl truncate umount unshare uptime watch who
 
 The complement  of ubase  is sbase[1] which  mostly follows  POSIX and
 provides all the portable tools.  Together they are intended to form a

TODO

@@ -6,7 +6,6 @@ Tools
  * swaplabel(8)
  * last(1)
  * losetup(8)
- * sysctl
  * lspci
  * mkswap [-L]
  * passwd

sysctl.8

@@ -0,0 +1,9 @@
+.TH SYSCTL 8 ubase-VERSION
+.SH NAME
+\fBsysctl\fR - Configure kernel parameters at runtime
+.SH SYNOPSIS
+\fBsysctl\fR \fIvariable\fR[=\fIvalue\fR]...
+.SH DESCRIPTION
+\fBsysctl\fR modifies kernel parameters at runtime.  The parameters available
+are those listed under \fI/proc/sys/\fR.  Procfs is required for sysctl support
+in Linux.  You can use \fBsysctl\fR to both read and write sysctl data.

sysctl.c

@@ -0,0 +1,139 @@
+/* See LICENSE file for copyright and license details. */
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include "util.h"
+
+static int
+getsysctl(char *variable, char **value)
+{
+	char path[PATH_MAX];
+	char *p;
+	char *buf;
+	int fd;
+	ssize_t n;
+
+	for (p = variable; *p; p++)
+		if (*p == '.')
+			*p = '/';
+
+	strlcpy(path, "/proc/sys/", sizeof(path));
+	if (strlcat(path, variable, sizeof(path)) >= sizeof(path))
+		return -1;
+
+	fd = open(path, O_RDONLY);
+	if (fd < 0)
+		return -1;
+
+	buf = malloc(1024);
+	if (!buf) {
+		close(fd);
+		return -1;
+	}
+
+	n = read(fd, buf, 1023);
+	if (n <= 0) {
+		close(fd);
+		free(buf);
+		return -1;
+	}
+	buf[n] = '\0';
+
+	p = strrchr(buf, '\n');
+	if (p)
+		*p = '\0';
+
+	*value = buf;
+
+	close(fd);
+
+	return 0;
+}
+
+static int
+setsysctl(char *variable, char *value)
+{
+	char path[PATH_MAX];
+	char *p;
+	int fd;
+	ssize_t n;
+
+	for (p = variable; *p; p++)
+		if (*p == '.')
+			*p = '/';
+
+	strlcpy(path, "/proc/sys/", sizeof(path));
+	if (strlcat(path, variable, sizeof(path)) >= sizeof(path))
+		return -1;
+
+	fd = open(path, O_WRONLY);
+	if (fd < 0)
+		return -1;
+
+	n = write(fd, value, strlen(value));
+	if (n != (ssize_t)strlen(value)) {
+		close(fd);
+		return -1;
+	}
+
+	close(fd);
+
+	return 0;
+}
+
+static void
+usage(void)
+{
+	eprintf("usage: %s variable[=value]...\n", argv0);
+}
+
+int
+main(int argc, char *argv[])
+{
+	char *variable;
+	char *value;
+	char *p;
+	int i;
+
+	argv0 = argv[0];
+	argv++;
+	argc--;
+
+	if (argc < 1)
+		usage();
+
+	for (i = 0; i < argc; i++) {
+		value = NULL;
+		variable = argv[i];
+		p = strchr(variable, '=');
+		if (p) {
+			if (p[1] == '\0') {
+				weprintf("malformed sysctl: %s\n", argv[i]);
+				continue;
+			}
+			*p = '\0';
+			value = &p[1];
+		}
+		if (variable) {
+			if (value) {
+				if (setsysctl(variable, value) < 0) {
+					weprintf("failed to set sysctl for %s\n", variable);
+					continue;
+				}
+			}
+			else {
+				if (getsysctl(variable, &value) < 0) {
+					weprintf("failed to get sysctl for %s\n", variable);
+					continue;
+				}
+				printf("%s = %s\n", variable, value);
+				free(value);
+			}
+		}
+	}
+
+	return EXIT_SUCCESS;
+}