linux-kernel - Re: [patch] scsi: revert "[SCSI] Get rid of scsi

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Message-ID: <4780FF85.4020501@panasas.com>
Date:	Sun, 06 Jan 2008 18:19:17 +0200
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Matthew Wilcox <matthew@....cx>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Osterlund <petero2@...ia.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [patch] scsi: revert "[SCSI] Get rid of scsi_cmnd->done"

On Sun, Jan 06 2008 at 5:43 +0200, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> 
> This all still leaves the question unanswered why that commit 
> 6f5391c283d7fdcf24bf40786ea79061919d1e1d changed any behaviour at all. 
> Because the thing that Peter is describing has nothing to do with any 
> low-level drivers what-so-ever.
> 
> 		Linus
> 

James Matthew.
I have a (very) wild guess at what maybe have changed with the cmnd->done
patch:

Do you remember the effective loop in scsi_lib:scsi_end_request() where
if bufflen was smaller then original request size, do to truncation
of bufflen by ULD, then the remaining of the request is re-queued again
as a new scsi-command. Well I think that the old system would call
cmnd->done for every iteration, and the new system, since the done is
called by the block-Q, does not see the resubmit of the new command.

I have not followed all code path of the matter, but I know that sr does
alters bufflen in some cases. 
All this is not a bug in itself, but it is a change in behavior that might 
cause the current sr hack to fail.

Boaz
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