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Fill in the Usage Page and Usage on Linux with hidraw
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Adapted from ApeironTuska's PR to PastaJ36/hidapi (PastaJ36/hidapi#1)
Which was adapted from djpnewton's PR to signal11/hidapi (signal11/hidapi#6)

Also addresses some of the issues mentioned in (signal11/hidapi#6)
* hid_open_path and hid_enumerate both need to retrieve the usage page
as the user may call hid_open_path directly without using hid_enumerate
* Now using uses_numbered_reports() instead of duplicated code

Includes additional interface fields that are useful in Linux when it's
not possible (undesireable) to unbind the HID interface during a scan.
* iInterface (only some devices use this, but can be very useful)
* bInterfaceClass
* bInterfaceSubClass
* bInterfaceProtocol
* bNumEndpoints

TODO - macOS and Windows
TODO - Test hid and libusb usage and usage page
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@haata
haata committed Jan 19, 2020
1 parent 7d9b4dc commit a27a6c2
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Showing 2 changed files with 153 additions and 17 deletions.
6 changes: 4 additions & 2 deletions hidapi/hidapi.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -65,10 +65,12 @@ extern "C" {
/** Product string */
wchar_t *product_string;
/** Usage Page for this Device/Interface
(Windows/Mac only). */
(Windows/Mac only)
(Linux if unbound)*/
unsigned short usage_page;
/** Usage for this Device/Interface
(Windows/Mac only).*/
(Windows/Mac only)
(Linux if unbound)*/
unsigned short usage;
/** The USB interface which this logical device
represents.
Expand Down
164 changes: 149 additions & 15 deletions linux/hid.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -183,7 +183,7 @@ static int uses_numbered_reports(__u8 *report_descriptor, __u32 size) {
return 1;
}

//printf("key: %02hhx\n", key);
printf("key: %02hhx\n", key);

if ((key & 0xf0) == 0xf0) {
/* This is a Long Item. The next byte contains the
Expand Down Expand Up @@ -228,6 +228,132 @@ static int uses_numbered_reports(__u8 *report_descriptor, __u32 size) {
return 0;
}

/*
* Get bytes from a HID Report Descriptor.
* Only call with a num_bytes of 0, 1, 2, or 4.
*/
static __u32 get_bytes(__u8 *rpt, size_t len, size_t num_bytes, size_t cur)
{
/* Return if there aren't enough bytes. */
if (cur + num_bytes >= len)
return 0;

if (num_bytes == 0)
return 0;
else if (num_bytes == 1)
return rpt[cur + 1];
else if (num_bytes == 2)
return (rpt[cur + 2] * 256 + rpt[cur + 1]);
else if (num_bytes == 4)
return (rpt[cur + 4] * 0x01000000 +
rpt[cur + 3] * 0x00010000 +
rpt[cur + 2] * 0x00000100 +
rpt[cur + 1] * 0x00000001);
else
return 0;
}

/*
* Retrieves the device's Usage Page and Usage from the report
* descriptor. The algorithm is simple, as it just returns the first
* Usage and Usage Page that it finds in the descriptor.
* The return value is 0 on success and -1 on failure.
*/
static int get_usage(__u8 *report_descriptor, size_t size, unsigned short *usage_page, unsigned short *usage)
{
int i = 0;
int size_code;
int data_len, key_size;
int usage_found = 0, usage_page_found = 0;
printf("GETTT");

while (i < size) {
int key = report_descriptor[i];
int key_cmd = key & 0xfc;
printf("key: %02hhx\n", key);

if ((key & 0xf0) == 0xf0) {
/*
* This is a Long Item. The next byte contains the
* length of the data section (value) for this key.
* See the HID specification, version 1.11, section
* 6.2.2.3, titled "Long Items."
*/
if (i + 1 < size)
data_len = report_descriptor[i + 1];
else
data_len = 0; /* malformed report */
key_size = 3;
}
else {
/*
* This is a Short Item. The bottom two bits of the
* key contain the size code for the data section
* (value) for this key. Refer to the HID
* specification, version 1.11, section 6.2.2.2,
* titled "Short Items."
*/
size_code = key & 0x3;
switch (size_code) {
case 0:
case 1:
case 2:
data_len = size_code;
break;
case 3:
data_len = 4;
break;
default:
/* Can't ever happen since size_code is & 0x3 */
data_len = 0;
break;
};
key_size = 1;
}

if (key_cmd == 0x4) {
*usage_page = get_bytes(report_descriptor, size, data_len, i);
usage_page_found = 1;
}
if (key_cmd == 0x8) {
*usage = get_bytes(report_descriptor, size, data_len, i);
usage_found = 1;
}

if (usage_page_found && usage_found)
return 0; /* success */

/* Skip over this key and it's associated data */
i += data_len + key_size;
}

return -1; /* failure */
}

static int get_report_descriptor(int device_handle, struct hidraw_report_descriptor *rpt_desc)
{
int res, desc_size = 0;

memset(rpt_desc, 0x0, sizeof(*rpt_desc));

/* Get Report Descriptor Size */
res = ioctl(device_handle, HIDIOCGRDESCSIZE, &desc_size);
if (res < 0) {
register_global_error_format("ioctl (GRDESCSIZE): %s", strerror(errno));
return res;
}

/* Get Report Descriptor */
rpt_desc->size = desc_size;
res = ioctl(device_handle, HIDIOCGRDESC, &rpt_desc);
if (res < 0) {
register_global_error_format("ioctl (GRDESC): %s", strerror(errno));
return res;
}

return res;
}

/*
* The caller is responsible for free()ing the (newly-allocated) character
* strings pointed to by serial_number_utf8 and product_name_utf8 after use.
Expand Down Expand Up @@ -567,6 +693,25 @@ struct hid_device_info HID_API_EXPORT *hid_enumerate(unsigned short vendor_id,
cur_dev->manufacturer_string = copy_udev_string(usb_dev, device_string_names[DEVICE_STRING_MANUFACTURER]);
cur_dev->product_string = copy_udev_string(usb_dev, device_string_names[DEVICE_STRING_PRODUCT]);

/* Usage Page and Usage */
int res;
struct hidraw_report_descriptor rpt_desc;
int device_handle = open(dev_path, O_RDWR);
if (device_handle > 0) {
res = get_report_descriptor(device_handle, &rpt_desc);
if (res >= 0) {
unsigned short page = 0, usage = 0;
/*
* Parse the usage and usage page
* out of the report descriptor.
*/
get_usage(rpt_desc.value, rpt_desc.size, &page, &usage);
cur_dev->usage_page = page;
cur_dev->usage = usage;
}
close(device_handle);
}

/* Release Number */
str = udev_device_get_sysattr_value(usb_dev, "bcdDevice");
cur_dev->release_number = (str)? strtol(str, NULL, 16): 0x0;
Expand Down Expand Up @@ -736,22 +881,11 @@ hid_device * HID_API_EXPORT hid_open_path(const char *path)
register_device_error(dev, NULL);

/* Get the report descriptor */
int res, desc_size = 0;
int res;
struct hidraw_report_descriptor rpt_desc;

memset(&rpt_desc, 0x0, sizeof(rpt_desc));

/* Get Report Descriptor Size */
res = ioctl(dev->device_handle, HIDIOCGRDESCSIZE, &desc_size);
if (res < 0)
register_device_error_format(dev, "ioctl (GRDESCSIZE): %s", strerror(errno));

/* Get Report Descriptor */
rpt_desc.size = desc_size;
res = ioctl(dev->device_handle, HIDIOCGRDESC, &rpt_desc);
if (res < 0) {
register_device_error_format(dev, "ioctl (GRDESC): %s", strerror(errno));
} else {
res = get_report_descriptor(dev->device_handle, &rpt_desc);
if (res >= 0) {
/* Determine if this device uses numbered reports. */
dev->uses_numbered_reports =
uses_numbered_reports(rpt_desc.value,
Expand Down

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