RE: iSCSI Data Integrity - Digests

["Douglas Otis" <dotis@sanlight.net>]

<snip>
> While the gurus of TCP can quickly point out that it is
> impossible for URG pointer to mark the SCSI command boundary in the BSD
> implementation, there is nothing preventing two iSCSI adapters from using
> URG pointer when they send command PDUs to each other.  In fact,
> whether two
> iSCSI adapters using URG pointer in their exchanges, IMHO, is even outside
> the jurisdiction of this WG.  Because the use of URG pointer does not
> violate TCP protocol.  It is just that old TCP implementations not able to
> keep command/status PDUs in separate segments can not benefit from URG
> pointer.

I see a spark of life still lives in hopes of redefining the Urgent pointer.
A problem you will see is this pointer is only 16 bits.  As it is defined to
coalesce should new points become defined, it takes a small backlog in the
TCP stack to create a pointer that can not reach a point being defined at
the API.  To use the Urgent pointer as a message marker, this issue has been
decided and, in short, your conclusion about the ability to use the urgent
pointer in the manner you wish is re-inventing TCP and not to be done.  If
you wish such non-standard implementations of TCP, it clearly is outside the
benefits of this WG.

Doug


> Therefore, while an iSCSI adapter can interoperate with a client
> running in
> TCP of BSD 4.3, it should also be able to interoperate with another
> state-of-art iSCSI adapter which is much more intelligent.  The difference
> in their interoperation will be decided at login with text messages.  I
> think we don't have to limit ourselves to stone age tools if electrical
> drill is already invented.  Please note that I am not asking the invention
> of new TCP options here.
>
> Y.P.