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hidraw: report only Top-Level Usage_page/Usage pairs as 'unique' devi…
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…ces (#601)

- unique Top-Level Usage_page/Usage: to be consistent with Windows/macOS (OS-level implementations).
- support for single Usage Page item for several UsageIDs; 
- support for 32bit Usage items;

Fixes: #298
Fixes: #454
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@Youw
Youw committed Aug 26, 2023
1 parent 09ab35f commit 8a4de63
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Showing 2 changed files with 101 additions and 36 deletions.
12 changes: 10 additions & 2 deletions libusb/hid.c
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Original file line number Diff line number Diff line change
Expand Up @@ -250,8 +250,16 @@ static int get_usage(uint8_t *report_descriptor, size_t size,
//printf("Usage Page: %x\n", (uint32_t)*usage_page);
}
if (key_cmd == 0x8) {
*usage = get_bytes(report_descriptor, size, data_len, i);
usage_found = 1;
if (data_len == 4) { /* Usages 5.5 / Usage Page 6.2.2.7 */
*usage_page = get_bytes(report_descriptor, size, 2, i + 2);
usage_page_found = 1;
*usage = get_bytes(report_descriptor, size, 2, i);
usage_found = 1;
}
else {
*usage = get_bytes(report_descriptor, size, data_len, i);
usage_found = 1;
}
//printf("Usage: %x\n", (uint32_t)*usage);
}

Expand Down
125 changes: 91 additions & 34 deletions linux/hid.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -192,7 +192,7 @@ static wchar_t *copy_udev_string(struct udev_device *dev, const char *udev_name)
* Returns 1 if successful, 0 if an invalid key
* Sets data_len and key_size when successful
*/
static int get_hid_item_size(__u8 *report_descriptor, unsigned int pos, __u32 size, int *data_len, int *key_size)
static int get_hid_item_size(const __u8 *report_descriptor, __u32 size, unsigned int pos, int *data_len, int *key_size)
{
int key = report_descriptor[pos];
int size_code;
Expand Down Expand Up @@ -248,7 +248,7 @@ static int get_hid_item_size(__u8 *report_descriptor, unsigned int pos, __u32 si
* Get bytes from a HID Report Descriptor.
* Only call with a num_bytes of 0, 1, 2, or 4.
*/
static __u32 get_hid_report_bytes(__u8 *rpt, size_t len, size_t num_bytes, size_t cur)
static __u32 get_hid_report_bytes(const __u8 *rpt, size_t len, size_t num_bytes, size_t cur)
{
/* Return if there aren't enough bytes. */
if (cur + num_bytes >= len)
Expand All @@ -271,6 +271,60 @@ static __u32 get_hid_report_bytes(__u8 *rpt, size_t len, size_t num_bytes, size_
return 0;
}

/*
* Iterates until the end of a Collection.
* Assumes that *pos is exactly at the beginning of a Collection.
* Skips all nested Collection, i.e. iterates until the end of current level Collection.
*
* The return value is non-0 when an end of current Collection is found,
* 0 when error is occured (broken Descriptor, end of a Collection is found before its begin,
* or no Collection is found at all).
*/
static int hid_iterate_over_collection(const __u8 *report_descriptor, __u32 size, unsigned int *pos, int *data_len, int *key_size)
{
int collection_level = 0;

while (*pos < size) {
int key = report_descriptor[*pos];
int key_cmd = key & 0xfc;

/* Determine data_len and key_size */
if (!get_hid_item_size(report_descriptor, size, *pos, data_len, key_size))
return 0; /* malformed report */

switch (key_cmd) {
case 0xa0: /* Collection 6.2.2.4 (Main) */
collection_level++;
break;
case 0xc0: /* End Collection 6.2.2.4 (Main) */
collection_level--;
break;
}

if (collection_level < 0) {
/* Broken descriptor or someone is using this function wrong,
* i.e. should be called exactly at the collection start */
return 0;
}

if (collection_level == 0) {
/* Found it!
* Also possible when called not at the collection start, but should not happen if used correctly */
return 1;
}

*pos += *data_len + *key_size;
}

return 0; /* Did not find the end of a Collection */
}

struct hid_usage_iterator {
unsigned int pos;
int usage_page_found;
unsigned short usage_page;
};

/*
* Retrieves the device's Usage Page and Usage from the report descriptor.
* The algorithm returns the current Usage Page/Usage pair whenever a new
Expand All @@ -288,63 +342,64 @@ static __u32 get_hid_report_bytes(__u8 *rpt, size_t len, size_t num_bytes, size_
* 1 when finished processing descriptor.
* -1 on a malformed report.
*/
static int get_next_hid_usage(__u8 *report_descriptor, __u32 size, unsigned int *pos, unsigned short *usage_page, unsigned short *usage)
static int get_next_hid_usage(const __u8 *report_descriptor, __u32 size, struct hid_usage_iterator *ctx, unsigned short *usage_page, unsigned short *usage)
{
int data_len, key_size;
int initial = *pos == 0; /* Used to handle case where no top-level application collection is defined */
int usage_pair_ready = 0;
int initial = ctx->pos == 0; /* Used to handle case where no top-level application collection is defined */

/* Usage is a Local Item, it must be set before each Main Item (Collection) before a pair is returned */
int usage_found = 0;

while (*pos < size) {
int key = report_descriptor[*pos];
while (ctx->pos < size) {
int key = report_descriptor[ctx->pos];
int key_cmd = key & 0xfc;

/* Determine data_len and key_size */
if (!get_hid_item_size(report_descriptor, *pos, size, &data_len, &key_size))
if (!get_hid_item_size(report_descriptor, size, ctx->pos, &data_len, &key_size))
return -1; /* malformed report */

switch (key_cmd) {
case 0x4: /* Usage Page 6.2.2.7 (Global) */
*usage_page = get_hid_report_bytes(report_descriptor, size, data_len, *pos);
ctx->usage_page = get_hid_report_bytes(report_descriptor, size, data_len, ctx->pos);
ctx->usage_page_found = 1;
break;

case 0x8: /* Usage 6.2.2.8 (Local) */
*usage = get_hid_report_bytes(report_descriptor, size, data_len, *pos);
usage_found = 1;
if (data_len == 4) { /* Usages 5.5 / Usage Page 6.2.2.7 */
ctx->usage_page = get_hid_report_bytes(report_descriptor, size, 2, ctx->pos + 2);
ctx->usage_page_found = 1;
*usage = get_hid_report_bytes(report_descriptor, size, 2, ctx->pos);
usage_found = 1;
}
else {
*usage = get_hid_report_bytes(report_descriptor, size, data_len, ctx->pos);
usage_found = 1;
}
break;

case 0xa0: /* Collection 6.2.2.4 (Main) */
/* A Usage Item (Local) must be found for the pair to be valid */
if (usage_found)
usage_pair_ready = 1;
if (!hid_iterate_over_collection(report_descriptor, size, &ctx->pos, &data_len, &key_size)) {
return -1;
}

/* Usage is a Local Item, unset it */
usage_found = 0;
break;
/* A pair is valid - to be reported when Collection is found */
if (usage_found && ctx->usage_page_found) {
*usage_page = ctx->usage_page;
return 0;
}

case 0x80: /* Input 6.2.2.4 (Main) */
case 0x90: /* Output 6.2.2.4 (Main) */
case 0xb0: /* Feature 6.2.2.4 (Main) */
case 0xc0: /* End Collection 6.2.2.4 (Main) */
/* Usage is a Local Item, unset it */
usage_found = 0;
break;
}

/* Skip over this key and its associated data */
*pos += data_len + key_size;

/* Return usage pair */
if (usage_pair_ready)
return 0;
ctx->pos += data_len + key_size;
}

/* If no top-level application collection is found and usage page/usage pair is found, pair is valid
https://docs.microsoft.com/en-us/windows-hardware/drivers/hid/top-level-collections */
if (initial && usage_found)
return 0; /* success */
if (initial && usage_found && ctx->usage_page_found) {
*usage_page = ctx->usage_page;
return 0; /* success */
}

return 1; /* finished processing */
}
Expand Down Expand Up @@ -727,12 +782,14 @@ static struct hid_device_info * create_device_info_for_device(struct udev_device
result = get_hid_report_descriptor_from_sysfs(sysfs_path, &report_desc);
if (result >= 0) {
unsigned short page = 0, usage = 0;
unsigned int pos = 0;
struct hid_usage_iterator usage_iterator;
memset(&usage_iterator, 0, sizeof(usage_iterator));

/*
* Parse the first usage and usage page
* out of the report descriptor.
*/
if (!get_next_hid_usage(report_desc.value, report_desc.size, &pos, &page, &usage)) {
if (!get_next_hid_usage(report_desc.value, report_desc.size, &usage_iterator, &page, &usage)) {
cur_dev->usage_page = page;
cur_dev->usage = usage;
}
Expand All @@ -741,7 +798,7 @@ static struct hid_device_info * create_device_info_for_device(struct udev_device
* Parse any additional usage and usage pages
* out of the report descriptor.
*/
while (!get_next_hid_usage(report_desc.value, report_desc.size, &pos, &page, &usage)) {
while (!get_next_hid_usage(report_desc.value, report_desc.size, &usage_iterator, &page, &usage)) {
/* Create new record for additional usage pairs */
struct hid_device_info *tmp = (struct hid_device_info*) calloc(1, sizeof(struct hid_device_info));
struct hid_device_info *prev_dev = cur_dev;
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