Re: Proposals to change the way all drivers work with SCSI commands

[Stefan Richter <stefanr@s5r6.in-berlin.de>]

Kristian Høgsberg wrote:
> On 5/11/07, Stefan Richter <stefanr@s5r6.in-berlin.de> wrote:
>> James Bottomley wrote:
>> > It strikes me that in all of this, we could also consider doing the DMA
>> > mapping inside the mid layer (instead of in every driver).
...
>> The old SBP-2 driver needs the virtual addresses of S/G elements if
>> compiled with a certain config option.  This option is meant for use
>> with FireWire controllers which do not implement OHCI-1394, or to run
>> the IEEE 1394 stack in a more secure mode.
...
> Well, if we want to make a more secure mode for fw-sbp2.c where it,
> like the old driver, manually copies the payload data from the general
> async receive buffer to the destination, we'll still need the virtual
> address.

Yes, that's right. /If/ we are going to implement such a mode, then (a)
the virtual addresses have to be passed down to ->queuecommand, and (b)
DMA mapping would be unnecessary and wasteful.

(For the list:  By "secure" we mean that we wouldn't allow the FireWire
controller to act as a bus bridge, and would be able to do boundary
checks on local bus addresses which, in the SBP-2 protocol, are
generally coming from the _target_.  Without such a mode, the lower 4G
of the initiator's memory are at the mercy of the target's firmware.)

> How does the usb storage driver handle this?
> 
> Kristian

-- 
Stefan Richter
-=====-=-=== -=-= -=-==
http://arcgraph.de/sr/
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