Re: Reg: Bidirectional command format ?

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On Jun 16, 2006, at 5:37 AM, Praveen Madhavan wrote:

> Hi Folks,
>
> Can any one point me the frame format of bidirectional command in  
> case of iSCSI & FCP ?.. I was trying to route bidirectional command  
> recv'd from iSCSI initiator to FC Target..
>
> Here is the iSCSI PDU format for bi-direct command recv from initiator
> ---------------------------------------------------------------------- 
> --------------------------
> |        BHS 
> (48bytes)                                                              
>        |
> |        R & W bit set to  
> ONE,                                                        |
> |        Expected xfer len =  
> 0x200                                                  |
> |        Total AHS Length = 2 
> (8bytes)                                             |
> |        SCSI CDB = Write(10)  Transfer length = 00 01 ( 512 bytes)  |
>   
> ---------------------------------------------------------------------- 
> --------------------------|
> |        AHS ( 8  
> bytes)                                                                 
>    |
> |        Expected Read data length = 0x200(512  
> bytes)                    |
> ---------------------------------------------------------------------- 
> ----------------------------
>
> Here is the FCP format for bi-direct command that i frame for  
> sending it to target.
>
> ---------------------------------------------------------------------- 
> --------------------------
> |        FC-Header  
> (24bytes)                                                          |
> |--------------------------------------------------------------------- 
> ---------------------------
> |        FCP-Header(36  
> bytes)                                                        |
> |         R & W bit set to  
> ONE,                                                       |
> |        Additional CDB length =  
> 0                                                   |
> |        SCSI CDB = Write(10)  Transfer length = 00 01 ( 512  
> bytes)   |
> |        FCP_DL  = 0x200 ( 512  
> bytes)                                             |
> |        FCP_BIDIRECTIONAL_READ_DL = 0x200(512)                     |
>   
> ---------------------------------------------------------------------- 
> ---------------------------|
>
> Well, I am not quite sure about the CDB values in case Bidir  
> commands..
> Will Bi directional cmds use Write CDB(10) or Read CDB (10) ? ..

No. Read and Write in normal sizes (6, 10, 12, 16) are unidirectional.

Each specific command has either no data phase (test unit ready), has  
at most a data-out phase (Write for instance), at most a data-in  
phase (Read), or is bidirectional.

> How can i control following bidi- operation in case of iSCSI & FCP ?
> 1.bidirectional command with read before write operation
> 2.bidirectional command with write before read operation

You really don't need to do anything different for BiDi commands,  
other than be able to keep both a Write and a Read residual. As you  
note, the SCSI Command Request will indicate what data phases the  
initiator expects, you need only map them along.

How does the target announce/control data flow in FCP? You need only  
pass that information on to the iSCSI layer. If the FCP target sends  
you data, then you send the initiator a bunch of Data-In PDUs.  
However it is that FCP controls data openings translates into R2Ts to  
the iSCSI initiator.

Take care,

Bill
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