linux-kernel - Re: [PATCH v3 4/4] scsi_debug: fix do_device

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Date:	Tue, 25 Jun 2013 01:34:46 +0200
From:	Douglas Gilbert <dgilbert@...erlog.com>
To:	Akinobu Mita <akinobu.mita@...il.com>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH v3 4/4] scsi_debug: fix do_device_access() with wrap around
 range

On 13-06-23 02:37 PM, Akinobu Mita wrote:
> do_device_access() is a function that abstracts copying SG list from/to
> ramdisk storage (fake_storep).
>
> It must deal with the ranges exceeding actual fake_storep size, because
> such ranges are valid if virtual_gb is set greater than zero, and they
> should be treated as fake_storep is repeatedly mirrored up to virtual size.
>
> Unfortunately, it can't deal with the range which wraps around the end of
> fake_storep. A wrap around range is copied by two sg_copy_{from,to}_buffer()
> calls, but sg_copy_{from,to}_buffer() can't copy from/to in the middle of
> SG list, therefore the second call can't copy correctly.
>
> This fixes it by using sg_pcopy_{from,to}_buffer() that can copy from/to
> the middle of SG list.
>
> This also simplifies the assignment of sdb->resid in fill_from_dev_buffer().
> Because fill_from_dev_buffer() is now only called once per command
> execution cycle.  So it is not necessary to take care to decrease
> sdb->resid if fill_from_dev_buffer() is called more than once.
>
> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> Cc: "James E.J. Bottomley" <JBottomley@...allels.com>
> Cc: Douglas Gilbert <dgilbert@...erlog.com>
> Cc: linux-scsi@...r.kernel.org
> ---
>
> * No change from v2

Acked-by: Douglas Gilbert <dgilbert@...erlog.com>

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