The ioLength for a submitted request will the the amount of data requested in
the data stage. The ioLength for a completed request will be the actual amount
of data transferred in the data stage. It’s quite similar to any other data
pipe.
Just to note, it may be acceptable for a device to send less than the amount
requested so the values may differ between a submit and a complete. For
example, a usb ethernet driver could always perform reads of MTU sizes but the
actual amount read will usually be less.
—scott
> On Jan 5, 2017, at 9:32 PM, Guy Harris <g...@alum.mit.edu> wrote:
>
> On Dec 9, 2016, at 1:37 PM, Scott Deandrea <sdeand...@apple.com> wrote:
>
>> The link-layer header format is as follows:
>> struct
>> {
>> // Control information
>> uint16_t bcdVersion; // version of this structure
>> uint8_t headerLength; // length of this structure
>> uint8_t requestType; // tAppleUSBHostPacketFilterRequestType
>>
>> // Transfer information
>> uint32_t ioLength; // amount of data requested/transferred
>
> So, for a completed request - or a submitted request to the Default Control
> Pipe - does this have any relationship to the number of bytes of payload, or
> is the number of bytes of payload just "the on-the-wire length from the
> pcap/pcapng header minus the link-layer header length"?
>
> I.e., would checking that value against the actual number of bytes of payload
> in the packet, for completed requests and submitted request to the Default
> Control Pipe - be a useful error check, or should we just print that value
> without any interpretation or checking?
>
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