commit 8082251befdd1798cadc51b0e9e88bdfcc8cbd48
Author: Alessandro Mauri <alemauri001@gmail.com>
Date:   Wed Feb 16 17:01:51 2022 +0100

    initial commit

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..423d628
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+btor
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..17d3552
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,10 @@
+.POSIX:
+
+CC = gcc 
+CFLAGS = -Wall -Werror -Wextra -pedantic -std=c11
+
+btor: btor.c
+	${CC} ${LDFLAGS} ${CFLAGS} btor.c -o btor
+
+clean:
+	rm -f btor
diff --git a/btor.c b/btor.c
new file mode 100644
index 0000000..2756f4f
--- /dev/null
+++ b/btor.c
@@ -0,0 +1,99 @@
+#define _POSIX_C_SOURCE 200809l
+#define _DEFAULT_SOURCE
+
+#include <linux/input.h>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/epoll.h>
+#include <sys/ioctl.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <err.h>
+#include <string.h>
+#include <dirent.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#define test_bit(yalv, abs_b) ((((char *)abs_b)[yalv/8] & (1<<yalv%8)) > 0)
+
+#define EVDEV_ROOT "/dev/input/"
+
+int main(int argc, char **argv)
+{
+	(void)argc;
+	(void)argv;
+
+	DIR *dir = opendir(EVDEV_ROOT);
+	if (!dir)
+		err(1, "opendir:");
+	struct dirent *dp;
+	struct stat st = {0};
+	int stylus = -1;
+
+	while ((dp = readdir(dir)) != NULL) {
+		if (fstatat(dirfd(dir), dp->d_name, &st, 0) == -1)
+			err(1, "fstatat:");
+		if ((st.st_mode & S_IFMT) != S_IFCHR)
+			continue;
+
+		int tmp_fd = openat(dirfd(dir), dp->d_name, O_RDWR | O_NONBLOCK);
+		if (tmp_fd < 0)
+			err(1, "openat:");
+		union {
+			char b[EV_MAX];
+			char k[KEY_MAX];
+		} vec;
+		if (ioctl(tmp_fd, EVIOCGBIT(0, EV_MAX), vec.b) < 0)
+			err(1, "ioctl:");
+		if (!test_bit(EV_KEY, vec.b))
+			continue;
+		if (ioctl(tmp_fd, EVIOCGBIT(EV_KEY, KEY_MAX), vec.k) < 0)
+			err(1, "ioctl:");
+
+		if (test_bit(BTN_STYLUS, vec.k) && test_bit(EV_ABS, vec.k)) {
+			stylus = tmp_fd;
+			break;
+		}
+		close(tmp_fd);
+	}
+	closedir(dir);
+	if (stylus == -1)
+		err(1, "no stylus input found");
+
+	int poll_set = epoll_create(1);
+	if (poll_set < 0)
+		err(1, "epoll_create:");
+	struct epoll_event poll_ev = { .events = EPOLLIN | EPOLLOUT | EPOLLET };
+	if (epoll_ctl(poll_set, EPOLL_CTL_ADD, stylus, &poll_ev) < 0)
+		err(1, "epoll_ctl:");
+
+
+	unsigned char button_recived = 0;
+	struct input_event in_ev, out_ev;
+	while (epoll_wait(poll_set, &poll_ev, 1, -1) != -1) {
+		switch (poll_ev.events) {
+		case EPOLLIN:
+			if (read(stylus, &in_ev, sizeof(struct input_event)) < 0)
+				err(1, "read:");
+			if (in_ev.type != BTN_STYLUS)
+				break;
+			out_ev.type = BTN_TOOL_RUBBER;
+			out_ev.value = in_ev.value;
+			button_recived = 1;
+			break; 
+		case EPOLLOUT:
+			if (!button_recived)
+				break;
+			button_recived = 0;
+			if (write(stylus, &out_ev, sizeof(struct input_event)) < 0)
+				err(1, "write:");
+			break;			
+		default:
+			break;
+		}
+	}
+
+	return 0;
+}