RE: Framing Discussion

[Douglas Otis <dotis@sanlight.net>]

JP,

The VM page flipping will require blocks to be greater than or equal to
pages in size and that these blocks are aligned at page boundaries.  Neither
of these assumptions are true. The goal is clear, the NIC will examine the
content and then direct data payload to the system through the NIC
interface.  The desire is to keep the buffers on the NIC small and thus
allow out of sequence processing of the TCP stream.  This must be seen as a
modification to the normal TCP implementation.  Such operation should
include a complete description of the API to allow consideration of NIC
design, inter-operability and security requirements.

Doug


> >> The design goal behind the framing discussion
> >> is avoidance of that copy.  In contrast to the
> >> typical case for NICs and TCP/IP, read data
> >> buffers for SCSI data are usually *not*
> >> interchangeable.
> >>
> >Why are they not interchangeable ? This is an
> >assumption not stated anywhere.  Is there
> >a list of other assumptions that is documented ?
> >
>
> Typically, the original data buffer is with the application that
> made the SCSI READ request - and this buffer may not have been
> allocated with the constraints that should be ready for a simple
> swapping. Assuming that the constraints are met, it would require
> VM page flipping, which is considered to be an implementation hack.
>
> A protocol level solution to locate the buffer and its offset for
> the incoming TCP segment is probably a better thing to have.
>
> -JP
>
>