[Stgt-devel] [Ips] Calculating the VA in iSER header

[Eli Dorfman]

According to Mike's explanation below it seems that we have a bug in
iSER initiator.
Fixing this bug will require a fix in the stgt iSER code.

The problem is that the initiator send a VA which already includes an
offset for the unsolicited data (which is wrong).
In iser_initiator.c::iser_prepare_write_cmd the code looks like this:
hdr->write_va   = cpu_to_be64(regd_buf->reg.va + unsol_sz);

we think that it should be modified to:
hdr->write_va   = cpu_to_be64(regd_buf->reg.va);

Let's discuss this and verify we interpret the spec correctly.
If agreed we will send a patch.

Eli

2008/4/15 Mike Ko <mako at almaden.ibm.com>:
>
> VA is a concept introduced in an Infiniband annex to support iSER.  It
> appears in the expanded iSER header for Infiniband use only to support the
> non-Zero Based Virtual Address (non-ZBVA) used in Infiniband vs the ZBVA
> used in IETF.
>
> "The DataDescriptorOut describes the I/O buffer starting with the immediate
> unsolicited data (if any), followed by the non-immediate unsolicited data
> (if any) and solicited data."  If non-ZBVA mode is used, then VA points to
> the beginning of this buffer.  So in your example, the VA field in the
> expanded iSER header will be zero.  Note that for IETF, ZBVA is assumed and
> there is no provision to specify a different VA in the iSER header.
>
> Tagged offset (TO) refers to the offset within a tagged buffer in RDMA Write
> and RDMA Read Request Messages.  When sending non-immediate unsolicited
> data, Send Message types are used and the TO field is not present.  Instead,
> the buffer offset is appropriately represented by the Buffer Offset field in
> the SCSI Data-Out PDU.  Note that Tagged Offset is not the same as write VA
> and it does not appear in the iSER header.
>
> Mike
>
>
>
>  Erez Zilber <erezz at voltaire.com>
> Sent by: ips-bounces at ietf.org
>
> 04/15/2008 06:40 AM
>
> To ips at ietf.org
>
> cc
>
> Subject [Ips] Calculating the VA in iSER header
>
>
>
>
>
>
> We're trying to understand what should be the write VA (tagged offset)
>  in the iSER header for WRITE commands. If unsolicited data is to be
>  sent, should the VA be the original VA or should it be original VA +
>  FirstBurstLength?
>
>
>  Example:
>
>
>  InitialR2T=No
>
>  FirstBurstLength = 1000
>
>
>  Base address of the registered buffer = 0
>
>
>  Now, what should be the VA in the iSER header? 0 or 1000?
>
>
>  We read the following paragraph in the iSER spec, but didn't get an
>  answer from there:
>
>
>  * If there is solicited data to be transferred for the SCSI write or
>  bidirectional command, as indicated by the Expected Data Transfer
>  Length in the SCSI Command PDU exceeding the value of
>  UnsolicitedDataSize, the iSER layer at the initiator MUST do the
>  following:
>
>  a. It MUST allocate a Write STag for the I/O Buffer defined by
>  the qualifier DataDescriptorOut. The DataDescriptorOut
>  describes the I/O buffer starting with the immediate
>  unsolicited data (if any), followed by the non-immediate
>  unsolicited data (if any) and solicited data. This means
>  that the BufferOffset for the SCSI Data-out for this
>  command is equal to the TO. This implies that a zero TO
>  for this STag points to the beginning of this I/O Buffer.
>
>
>  Thanks,
>
>  --
>
>  ____________________________________________________________
>
>  Erez Zilber | 972-9-971-7689
>
>  Software Engineer, Storage Solutions
>
>  Voltaire ? _The Grid Backbone_
>
>  __
>
>  www.voltaire.com <http://www.voltaire.com/>
>
>
>
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