linux-kernel - Re: [PATCH 1/1] [usb/host]: use get/put_unaligned_* helpers to fix more potential unaligned issues.

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Date:	Thu, 15 May 2008 10:28:23 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Bryan Wu <cooloney@...nel.org>
cc:	Jie Zhang <jie.zhang@...log.com>,
	Oliver Neukum <oliver@...kum.org>, <harvey.harrison@...il.com>,
	<david-b@...bell.net>, <greg@...ah.com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] [usb/host]: use get/put_unaligned_* helpers to fix
 more potential unaligned issues.

On Thu, 15 May 2008, Bryan Wu wrote:

> >>>> What is supposed to make all these changes a good idea?
> >>>>
> >>> Since buf might not be 4-byte aligned.
> >>
> >> It is. Please analyze the code before you use these access methods.
> >>
> > You are right. buf has been 4-byte aligned since 2.6.19. My patch was
> > written two years ago. Sorry for the noise I caused.
> >
> 
> I has keeping this patch for a long time.  Jie fixed this patch at
> 2006/09/20 in our svn:
> http://blackfin.uclinux.org/git/?p=readonly-mirrors/linux-kernel.git;a=commit;h=cb3da1243f84b37b53486c7e86da34565b4c5d92
> http://blackfin.uclinux.org/git/?p=readonly-mirrors/linux-kernel.git;a=commit;h=2559298f0dca2cffc0b87390b92a484004f0d85e
> 
> And a similar patch from David Miller was accept in ohci-hub.c
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=92164c5dd1ade33f4e90b72e407910de6694de49
> 
> Also because of the same issue, which was fixed by:
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=54bee6e1b455573658972510a76119f279db32b7
> 
> If other functions not only rh_call_control() call this hub_control()
> pointer and the buf is not 4-byte aligned,
> this bug will fire again without the unaligned API. This patch is
> safer for the caller, although not efficient.

But the hub_control routines are almost never called by anything 
other than rh_call_control().  The only exception is in ehci_hub.c, and 
there the buf pointer is NULL.

So I don't see any need for this patch.

On the other hand, Jie could make a bunch of useful changes to
drivers/usb/gadget/file_storage.c, which has its own private routines
for unaligned little-endian access.

Alan Stern

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