G'day all,
Could someone please explain the functionality for device descriptor parsing
in usb.c?
I am specifically interested in usb_parse_endpoint(), usb_parse_interface()
and usb_parse_configuration(), and this code fragment:
/* If we find another descriptor which is at or below */
/* us in the descriptor heirarchy then return */
if ((header->bDescriptorType == USB_DT_INTERFACE) ||
(header->bDescriptorType == USB_DT_ENDPOINT) ||
(header->bDescriptorType == USB_DT_CONFIG) ||
(header->bDescriptorType == USB_DT_DEVICE))
break;
Issue 1:
What does the "descriptor hierachy" mean, (or how can "us" be at or below in
each case)?
Issue 2:
It looks like usb_parse_configuration() is br0ken. In this loop, if the extra
descriptor information isn't only in the last descriptor, then the previous
ones leak memory, and the extra information gets lost:
for (i = 0; i < config->bNumInterfaces; i++) {
int numskipped, len;
char *begin;
/* Skip over the rest of the Class Specific or Vendor */
/* Specific descriptors */
begin = buffer;
numskipped = 0;
while (size >= sizeof(struct usb_descriptor_header)) {
header = (struct usb_descriptor_header *)buffer;
if ((header->bLength > size) || (header->bLength < 2)) {
err("invalid descriptor length of %d",
header->bLength);
return -1;
}
/* If we find another descriptor which is at or below */
/* us in the descriptor heirarchy then we're done */
if ((header->bDescriptorType == USB_DT_ENDPOINT) ||
(header->bDescriptorType == USB_DT_INTERFACE) ||
(header->bDescriptorType == USB_DT_CONFIG) ||
(header->bDescriptorType == USB_DT_DEVICE))
break;
dbg("skipping descriptor 0x%X", header->bDescriptorType);
numskipped++;
buffer += header->bLength;
size -= header->bLength;
}
if (numskipped)
dbg("skipped %d class/vendor specific endpoint descriptors",
numskipped);
/* Copy any unknown descriptors into a storage area for */
/* drivers to later parse */
len = (int)(buffer - begin);
if (!len) {
config->extra = NULL;
config->extralen = 0;
} else {
config->extra = kmalloc(len, GFP_KERNEL);
if (!config->extra) {
err("couldn't allocate memory for config extra
descriptors");
config->extralen = 0;
return -1;
}
memcpy(config->extra, begin, len);
config->extralen = len;
}
retval = usb_parse_interface(dev, config->interface + i, buffer, size);
if (retval < 0)
return retval;
buffer += retval;
size -= retval;
}
Anyone enlighten me?
Brad
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