linux-kernel - Re: Scatter-gather list constraints

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Message-ID: <87fxr6yjl4.fsf@basil.nowhere.org>
Date:	Sat, 21 Jun 2008 15:59:51 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Kernel development list <linux-kernel@...r.kernel.org>,
	AntonioLin <antonio.lin@...ormicro.com>,
	David Vrabel <david.vrabel@....com>
Subject: Re: Scatter-gather list constraints

Alan Stern <stern@...land.harvard.edu> writes:

> This question arises in connection with wireless USB mass-storage
> devices.  The controller driver requires that all DMA segments
> in a transfer, other than the last one, have a multiple of 1024 bytes.  
> But we're sometimes getting s-g lists where an element contains an odd
> number of 512-byte sectors, and of course it doesn't work.

But you can handle a single 512 byte request? Splitting the request
in this case should work. Or maybe copying is cheaper than splitting?

I don't think the block layer knows about such kinds of restrictions.

-Andi
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