1 files changed, 77 insertions, 0 deletions
diff --git a/coreupdown.c b/coreupdown.c
new file mode 100644
index 0000000..1de5007
--- /dev/null
+++ b/coreupdown.c
@@ -0,0 +1,77 @@
+/* See LICENSE file for copyright and license details. */
+#include <ctype.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+int
+main(int argc, char *argv[])
+{
+	unsigned long i, count;
+	const char *command, *argv0;
+	char path[sizeof("/sys/devices/system/cpu/cpu/online") + 3 * sizeof(i)];
+	int fd, ret = 0;
+
+	if (argc == 0) {
+	wrong_command:
+		fprintf(stderr, "usage: coreup [count]\nusage: coredown [count]\n");
+		return 1;
+	}
+
+	argv0 = *argv++;
+	argc--;
+	command = strrchr(argv0, '/');
+	command = command ? &command[1] : argv0;
+
+	if (!strcmp(command, "coreup"))
+		count = ULONG_MAX;
+	else if (!strcmp(command, "coredown"))
+		count = 1;
+	else
+		goto wrong_command;
+
+	if (argc && !strcmp(argv[0], "--")) {
+		argv++;
+		argc--;
+	}
+
+	if (argc > 1) {
+	usage:
+		fprintf(stderr, "usage: %s [count]\n", argv0);
+		return 1;
+	}
+
+	if (argc >= 1) {
+		char *end;
+		errno = 0;
+		if (!isdigit(**argv))
+			goto usage;
+		count = strtoul(*argv, &end, 10);
+		if (!count || errno || *end)
+			goto usage;
+		argv++;
+		argc--;
+	}
+
+	for (i = 1; i; i++) {
+		sprintf(path, "/sys/devices/system/cpu/cpu%zu/online", i);
+		fd = open(path, O_WRONLY);
+		if (fd < 0) {
+			if (errno == ENOENT)
+				break;
+			fprintf(stderr, "%s: open %s O_WRONLY\n", argv0, path);
+			return 1;
+		}
+		if (write(fd, i < count ? "1\n" : "0\n", 2) < 0) {
+			fprintf(stderr, "%s: write %s\n", argv0, path);
+			ret = 1;
+		}
+		close(fd);
+	}
+
+	return ret;
+}