Re: [PATCH] mass storage : emulation of sat scsi_pass_thru with ATACB

From: Matthew Dharm
Date: Sat Mar 08 2008 - 16:24:18 EST


On Sat, Mar 08, 2008 at 09:08:26PM +0100, matthieu castet wrote:
> Hi Matthew,
>
> thanks for your comments
>
> Matthew Dharm wrote:
> >Why are you using an initializer instead of a new protocol code?
> Because using a new protocol code means I need to patch all the place
> where there is a comparison between us->subclass and US_SC_SCSI.
> After all I am US_SC_SCSI with a special case for ATA12 & ATA16 commands.
> I don't translate all scsi to atacb (that's what does US_SC_ISD200).

Yet, you call invoke_transport directly, just like any other protocol
handler.

The proper way to do this is as a separate protocol handler. If you want
to make it clear that you are only intercepting a couple of command types,
then don't call invoke_transport() directly, call the transparent scsi
protocol handler (which, of course, does the same thing but provides
clearer layering).

Oh, and you should add some "unlikely" tags to these if() conditionals.

> >Actually, why do you even have a separate 'dispatcher' function? Why not
> >just one protocol handler function which checks the command at the top and
> >calls invoke_transport there?
> What do you means by having a separate 'dispatcher' function?
> You means why I have 2 functions emulate_pass_thru_with_atacb and
> usb_stor_transparent_scsi_command_atacb ?
> I did 2 functions for having a code more clean.
>
> You suggest something like
> void usb_stor_transparent_scsi_command_atacb(struct scsi_cmnd *srb,
> struct us_data *us)
> {
> if (srb->cmnd[0] != ATA_16 && srb->cmnd[0] != ATA_12) {
> usb_stor_invoke_transport(srb, us);
> return;
> }
> copy emulate_pass_thru_with_atacb code here
> }

Yes, modulo my comment above about calling the transparent scsi protocol
handler instead of invoke_transport directly.

> >Also, unless ATACB is a new standard (and I don't think it is, as the
> >Cypress datasheet uses the term 'vendor specific'), then your functions
> >need renaming. Instead of 'emulate_pass_thru_with_atacb', how about
> >something like 'cypress_atacb' -- since it's already a protocol handler,
> >everyone already knows it's for passing commands.
> But 'emulate_pass_thru_with_atacb' only handle ATA pass_thru scsi
> commands. It doesn't translate all scsi commands to atacb like
> 'cypress_atacb' could suggest.
> That's why I put 'usb_stor_transparent_scsi_command_atacb' saying it is
> transparent_scsi_command + atacb support.

Yes, but your name suggests that ATACB is a new industry standard which is
implemented by more than a few chips from one specific vendor. That's not
acceptable.

Try 'cypress_atacb_passthrough' instead?

Matt

--
Matthew Dharm Home: mdharm-usb@xxxxxxxxxxxxxxxxxx
Maintainer, Linux USB Mass Storage Driver

P: Nine more messages in admin.policy.
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