linux-kernel - Re: compat ioctl32 for /dev/snapshot?

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Message-ID: <20090714095511.GF2076@elf.ucw.cz>
Date:	Tue, 14 Jul 2009 11:55:12 +0200
From:	Pavel Machek <pavel@....cz>
To:	Michael Tokarev <mjt@....msk.ru>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: compat ioctl32 for /dev/snapshot?

On Tue 2009-07-14 10:57:06, Michael Tokarev wrote:
> Pavel Machek wrote:
> []
>>> In order to (try to) check if it works or not, another userspace
>>> component has to be fixed to support 32/64 bit mode.  It's uswsusp,
>>> which currently assumes swap space structures are all 32bits.  So
>>> it isn't possible to immediately check if it works or not -- just
>>> ioctl(s) aren't enough.  Complete fix (kernel+user space) requires
>>> both, fixing all remaining (yet unknown) issues in old and new
>>> code on the way.
>>
>> Well, there seems to be single structure in s2disk; that does not seem
>> that hard to fix.
>
> Which one do you mean?

struct swsusp_info should be the one...

> Also, do you want to make it 32/64 bit clean in userspace too, so that
> an image produced by 32-bit s2disk can be read by 64bit resume and
> vise versa?  Sure it's good thing to have, to avoid possible issues
> with 32bit initramfs on 64bit system for example...

It would be cool, but...

>>> For now, I think it's best to let Pavel or Rafael to decide what
>>> to do with all this.
>>
>> I don't currently have easy access to 64bit machine, so I guess it is
>> up to someone else.
> []
>
> Ok.  I applied Arnd's patch again (with two fixes -- adding
> #include <linux/compat.h> and s/compat_ulong/compat_ulong_t/ and
> tried suspend/resume cycle with unmodified uswsusp-0.8.  Suspend
> worked (seemengly - it reported about 4G pages written, on a
> machine with 4G memory) but resume failed after reading all the
> pages and submitting them to /dev/snapshot.
>
> I've no time right now to debug it further (and again, yet again:
> I don't know the code, neither kernel nor userspace part).
>
> So I'd merge this change for now and deal with possible bugs later.
>
> At least there's no failed ioctl()s on /dev/snapshot anymore,
> neither at suspend nor at resume time.

ACK.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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