linux-kernel - Re: [PATCH] hid: Logitech G13 driver 0.0.4

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Date:	Mon, 25 Jan 2010 09:48:34 -0700
From:	"Rick L. Vinyard, Jr." <rvinyard@...nmsu.edu>
To:	"Oliver Neukum" <oliver@...kum.org>
Cc:	linux-kernel@...r.kernel.org, felipe.balbi@...ia.com, pavel@....cz,
	jayakumar.lkml@...il.com, linux-fbdev@...r.kernel.org,
	krzysztof.h1@...pl, akpm@...ux-foundation.org,
	linux-usb@...r.kernel.org, linux-input@...r.kernel.org,
	jkosina@...e.cz, dmitry.torokhov@...il.com
Subject: Re: [PATCH] hid: Logitech G13 driver 0.0.4

Oliver Neukum wrote:
> Am Mittwoch, 20. Januar 2010 21:47:22 schrieb Rick L. Vinyard Jr.:
>> +       if (copy_from_user(dst, buf, count))
>> +               err = -EFAULT;
>> +
>> +       if (!err)
>> +               *ppos += count;
>> +
>> +       g13_fb_update(par);
>> +
>> +       return (err) ? err : count;
>
> Do you really want to go on if you get -EFAULT?
>

Since the hecubafb driver (which I based this portion of the g13 driver
on) uses the same approach I tried to justify it myself when I first saw
it.

I don't know if this was the intent of the hecubafb author, but this is
the way I saw it.

By this point the copy_from_user() has failed. If it resulted in a partial
copy to dst then continuing on to an update can't hurt, and would reduce
display jitter if a re-write occurs from userspace. If a re-write doesn't
occur the virtual framebuffer is hosed anyways as dst is is the underlying
framebuffer.

Given that, the worst-case consequence seems to be an unnecessary update
to the device display.

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