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[dm-devel] Re: [stable] [2.6.24 PATCH 02/25] dm io:ctl use constant struct size



On Mon, Oct 15, 2007 at 09:34:09AM +0200, Arnd Bergmann wrote:
> On Monday 15 October 2007, Alasdair G Kergon wrote:
> > The underlying ABI is not changing, I hope - the trailing padding in the
> > struct should not affect the processing of the data by dm, and I see no
> > reason to continue maintaining the fiction that the 32-bit and 64-bit
> > ioctls are in some way incompatible with each other when they aren't
> > AFAIK.
> 
> It's a corner case of some sort, as DM uses ioctl numbers differently
> from most subsystems by splitting to code from the size argument
> during processing. Your change is certainly not an _incompatible_
> change to the ABI, but 32 bit binaries compiled against the new
> headers will use different ioctl numbers from those built against
> older headers.
> 
> This may break other code that expects a specific number, even
> if your handler does not care. The old compat code handles both
> variants (no variable size arguments), but /usr/bin/strace may have
> encoded only one set of numbers AFAICT.
> 
> > And yes, a follow-up patch can clean up our use of the compatibility
> > mechanism, going a little bit further than the patch you attached, I
> > hope.
> 
> Ok, sounds good. I don't think it's the kind of patch that should go
> into stable backports though.

Ok, I've not added this patch (2/25) to the queue at all.  If this is
incorrect, please let me know.

thanks,

greg k-h


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