Re: [Xen-devel] [PATCH RFC 09/23] lz4: add support for OSes that don't have asm/unaligned.h

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-04-23 at 11:06 +0200, Roger Pau Monnà wrote:
> On 23/04/14 10:53, Ian Campbell wrote:
> > On Tue, 2014-04-22 at 18:40 +0200, Roger Pau Monnà wrote:
> >> On 22/04/14 17:55, Ian Campbell wrote:
> >>> On Tue, 2014-04-22 at 16:46 +0200, Roger Pau Monnà wrote:
> >>>> Anyway, I think this patch and the preceding one are plain wrong, what
> >>>> we should do is completely remove the bogus dependence on
> >>>> asm/unaligned.h, which is a Linux specific header file, and open-code
> >>>> what we need.
> >>>
> >>> Am I right that for libxc's lz4 support we are using the Linux kernel's
> >>> built in decompression code, instead of the relevant userspace library
> >>> as we do for most other compression algorithms?
> >>
> >> No, I don't think we are using Linux kernel's built in decompression
> >> code,
> > 
> > Which library provides lz4_decompress_unknownoutputsize then?
> > 
> > It looks to me like xc_dom_decompress_lz4 gets it from #include
> > "../../xen/common/lz4/decompress.c" even in the !__MINIOS__ case and:
> >         $ head -n2 xen/common/lz4/decompress.c
> >         /*
> >          * LZ4 Decompressor for Linux kernel
> > 
> > i.e. this is Linux code (which Linux uses to decompress itself on boot)
> > copied into the hypervisor.
> > 
> > Since this is imported code we don't really want to rewrite it so we can
> > resync easily in the future. It's up to Xen and libxc to provide the
> > necessary scaffolding (in terms of helpers the unaligned accessors) to
> > make this code compile.
> 
> Yes, sorry I misunderstood you, I though you were saying that somehow
> Xen (or the tools), were relying on the Linux kernel to perform the
> decompression

Ah yes, I can see how that was confusing, sorry!

>  (which makes no sense).

Indeed.

> That's my plan, but instead of adding some crappy hack for OSes that
> don't have asm/unaligned.h, I would like to get rid of that dependency
> and code the helpers that we need.

In the scaffolding and not by modifying the imported code I pressume? In
which case, good thanks!

Ian.



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