Backlight control for thinkpad

.gitignore

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+*.o
+*.d
+rexbacklight
+*.swp

makefile

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+.PHONY: all
+all: rexbacklight
+
+rexbacklight: rexbacklight.c
+	gcc -std=c11 -O2 -Wall -Wextra -pedantic rexbacklight.c -o rexbacklight
+	strip --strip-all rexbacklight
+
+.PHONY: install
+install:
+	install -m4711 -o root -g root -s rexbacklight /usr/bin/rexbacklight
+
+.PHONY: clean
+clean:
+	rm rexbacklight

rexbacklight.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+void usage(void){
+	fprintf(stderr, "TODO: usage\n");
+	exit(-1);
+}
+
+int check_valid_files(const char* f1, const char* f2){
+	struct stat file1, file2;
+	if(stat(f1, &file1)){
+		printf("failed to open '%s'\n", f1);
+		return -1;
+	}
+	if(stat(f2, &file2)){
+		printf("failed to open '%s'\n", f2);
+		return -1;
+	}
+	//Same device and same inode means same file
+
+	//device id
+	if(file1.st_dev != file2.st_dev)
+		return -2;
+	//inode number
+	if(file1.st_ino != file2.st_ino)
+		return -2;
+	return 0;
+}
+
+int get_brightness(const char* file){
+	FILE* bright = fopen(file, "r");
+	char buff[127];
+	if(!bright){
+		fprintf(stderr, "Unable to open brightness file \"%s\"!\n", file);
+		return 0;
+	}
+	if(!fgets(buff, sizeof(buff), bright)){
+		fprintf(stderr, "Unable to read file \"%s\"!\n", file);
+		fclose(bright);
+		return 0;
+	}
+	fclose(bright);
+	return atof(buff);
+}
+
+//argv[1] shall be [+-=]<percentage>|min|max|off
+int main(int argc, char** argv){
+	const char* backlight_file     = "/sys/class/backlight/intel_backlight/brightness";
+	const char* max_backlight_file = "/sys/class/backlight/intel_backlight/max_brightness";
+
+	//Make sure we have an argument and it is at least 2 characters long
+	if(argc < 2 || strlen(argv[1]) < 2)
+		usage();
+
+	if(setuid(0)){
+		fprintf(stderr, "Unable to setuid to 0!\n");
+		return -3;
+	}
+
+	if(check_valid_files("/", "/proc/1/root")){
+		fprintf(stderr, "No chroot today\n");
+		return -4;
+	}
+
+	//Min brightness is just 0, so set it up front
+	float min_brightness = 0;
+	float max_brightness = get_brightness(max_backlight_file);
+	float current_brightness = get_brightness(backlight_file);
+
+	//Amount to inc/dec
+	int delta;
+	if(strlen(argv[1]) > 0)
+		delta = max_brightness * atof(argv[1] + 1) / 100.0;
+	else
+		delta = 0;
+
+	//Open brightness file for writing
+	FILE* bright = fopen(backlight_file, "w+");
+	if(!bright){
+		fprintf(stderr, "Unable to open brightness file \"%s\" for writing!\n", backlight_file);
+		return 1;
+	}
+
+	//Increment
+	if(argv[1][0] == '+'){
+		delta = delta + current_brightness;
+		if(delta >= max_brightness)
+			fprintf(bright, "%d", (int)max_brightness);
+		else{
+			fprintf(bright, "%d", delta);
+		}
+
+	//Decrement
+	}else if(argv[1][0] == '-'){
+		delta = current_brightness - delta;
+		if(delta <= min_brightness)
+			fprintf(bright, "%d", (int)min_brightness);
+		else
+			fprintf(bright, "%d", delta);
+
+	//Directly set
+	}else if(argv[1][0] == '='){
+		if(delta >= max_brightness)
+			fprintf(bright, "%d", (int)max_brightness);
+		else if(delta <= min_brightness)
+			fprintf(bright, "%d", (int)min_brightness);
+		else
+			fprintf(bright, "%d", delta);
+
+	//Set to minimum plus one (so backlight is actually on!)
+	}else if(!strcmp("min", argv[1])){
+		fprintf(bright, "%d", (int)(min_brightness + 1));
+
+	//Turn off backlight
+	}else if(!strcmp("off", argv[1])){
+		fprintf(bright, "%d", (int)min_brightness);
+
+	//Set to maximum
+	}else if(!strcmp("max", argv[1])){
+		fprintf(bright, "%d", (int)max_brightness);
+
+	//Unknown option
+	}else{
+		fclose(bright);
+		usage();
+	}
+	fclose(bright);
+	return 0;
+}