Re: DLT_ request

[Scott Deandrea <sdeandrea () apple com>]

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 <guy () alum mit edu> wrote:
>
> On Dec 9, 2016, at 1:37 PM, Scott Deandrea <sdeandrea () 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?

_______________________________________________
tcpdump-workers mailing list
tcpdump-workers () lists tcpdump org
https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers