Re: [patchset 0/5] Refactoring scsi_error to facilitate in synchronous REQUEST_SENSE

[Matthew Dharm <mdharm-scsi@one-eyed-alien.net>]

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On Mon, Sep 10, 2007 at 05:11:23PM +0300, Boaz Harrosh wrote:
> 
> In motivation to abstract scsi_cmnd members and insulate
> drivers/transports from scsi_cmnd internals. The last
> place left was the REQUEST_SENSE sequence when done
> synchronous, by drivers.

This probably isn't serious, but I noticed one thing (beyond what Alan's
analysis noted)...

I've always assumed that the scatterlist structs passed to an HCD were,
themselves, allocated from DMA-able memory.  That is, not just the transfer
buffers themselves, but the struct scatterlist also.

In this implementation, the struct scatterlist used for the single-element
transfer of the request sense buffer is part of the
struct scsi_eh_save_cmnd_info, which is allocated on the stack (for at
least usb-storage).  And, stack isn't DMA-able on all arches.

It is not a problem for usb-storage, since the struct scatterlists are
processed in code into a series of URBs, so nobody actually does DMA the
scatterlist structures.  However, I don't know enough about the other HCDs
to be certain about them.

Matt

-- 
Matthew Dharm                              Home: mdharm-usb@one-eyed-alien.net 
Maintainer, Linux USB Mass Storage Driver

Now payink attention, please.  This is mouse.  Click-click. Easy to 
use, da? Now you try...
					-- Pitr to Miranda
User Friendly, 10/11/1998

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