Re: [PATCH v1 3/3] TARGET/sbc,loopback: Adjust command data length in case pi exists on the wire

[Sagi Grimberg <sagig@dev.mellanox.co.il>]

On 6/11/2014 12:17 AM, Quinn Tran wrote:

<SNIP>

> QT> Instead of using existing value within cmd->data_length, can we
> calculated data_length based on secstors & blocksize.
>
> cmd->data_length = sectors * dev->dev_attrib.block_size;

We can do that I suppose...
Although it seems weird that the core discards the transport byte-count...
Just wandering if we should recalc on the DIF case only or always.

>
>  From the QLogic perfective, the cmd->data_length is pull directly from the
> wire (i.e. FCP header) when cmd is received.  In essence, it's whatever
> the Initiator is set it to.  We does not have any indicator to spot DIF vs
> none-DIF cmd when 1st received, unless the code do a peek.

Same for all transports I assume...

>
> With that said, the cmd->data_length does not guarantee to contain both
> "data length" & "protection length" when cmd is submit to
> TCM/target_submit_cmd().  In Dif-Insert mode, data_length will only
> contain the actual data(no Dif).

No, in the DOUT_INSERT/DIN_STRIP case, protect bits are off and the core 
will take the data length as is.
This case is covered.

> It's best that the SBC code re-calculate the actual data length and dif
> data length based on the number of sectors derived from the cmd.

Nic, what's your take on this?

Sagi.