samples/hid/hid_surface_dial.c

Source file repositories/reference/linux-study-clean/samples/hid/hid_surface_dial.c

File Facts

System
Linux kernel
Corpus path
samples/hid/hid_surface_dial.c
Extension
.c
Size
4498 bytes
Lines
204
Domain
Support Tooling And Documentation
Bucket
samples
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

struct haptic_syscall_args {
	unsigned int hid;
	int retval;
};

static void int_exit(int sig)
{
	running = false;
	exit(0);
}

static void usage(const char *prog)
{
	fprintf(stderr,
		"%s: %s [OPTIONS] /sys/bus/hid/devices/0BUS:0VID:0PID:00ID\n\n"
		"  OPTIONS:\n"
		"    -r N\t set the given resolution to the device (number of ticks per 360°)\n\n",
		__func__, prog);
	fprintf(stderr,
		"This program will morph the Microsoft Surface Dial into a mouse,\n"
		"and depending on the chosen resolution enable or not the haptic feedback:\n"
		"- a resolution (-r) of 3600 will report 3600 'ticks' in one full rotation\n"
		"  without haptic feedback\n"
		"- any other resolution will report N 'ticks' in a full rotation with haptic\n"
		"  feedback\n"
		"\n"
		"A good default for low resolution haptic scrolling is 72 (1 'tick' every 5\n"
		"degrees), and set to 3600 for smooth scrolling.\n");
}

static int get_hid_id(const char *path)
{
	const char *str_id, *dir;
	char uevent[1024];
	int fd;

	memset(uevent, 0, sizeof(uevent));
	snprintf(uevent, sizeof(uevent) - 1, "%s/uevent", path);

	fd = open(uevent, O_RDONLY | O_NONBLOCK);
	if (fd < 0)
		return -ENOENT;

	close(fd);

	dir = basename((char *)path);

	str_id = dir + sizeof("0003:0001:0A37.");
	return (int)strtol(str_id, NULL, 16);
}

static int set_haptic(struct hid_surface_dial *skel, int hid_id)
{
	struct haptic_syscall_args args = {
		.hid = hid_id,
		.retval = -1,
	};
	int haptic_fd, err;
	DECLARE_LIBBPF_OPTS(bpf_test_run_opts, tattr,
			    .ctx_in = &args,
			    .ctx_size_in = sizeof(args),
	);

	haptic_fd = bpf_program__fd(skel->progs.set_haptic);
	if (haptic_fd < 0) {
		fprintf(stderr, "can't locate haptic prog: %m\n");
		return 1;
	}

	err = bpf_prog_test_run_opts(haptic_fd, &tattr);
	if (err) {
		fprintf(stderr, "can't set haptic configuration to hid device %d: %m (err: %d)\n",
			hid_id, err);
		return 1;
	}
	return 0;
}

int main(int argc, char **argv)
{
	struct hid_surface_dial *skel;
	const char *optstr = "r:";
	struct bpf_link *link;
	const char *sysfs_path;
	int err, opt, hid_id, resolution = 72;

	while ((opt = getopt(argc, argv, optstr)) != -1) {
		switch (opt) {
		case 'r':
			{

Annotation

Implementation Notes