Messages in this thread | | | Date | Thu, 24 May 2007 19:50:02 +0530 | From | "Nitin Gupta" <> | Subject | Re: [RFC] LZO de/compression support - take 3 |
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On 5/24/07, Richard Purdie <richard@openedhand.com> wrote: > On Thu, 2007-05-24 at 01:04 +0530, Satyam Sharma wrote: > > On 5/23/07, Nitin Gupta <nitingupta910@gmail.com> wrote: > <snip>
> I remember this being mentioned. My answer was that this is the same > behaviour as the zlib library and you do not want to alloc/free this > memory every time you have a piece of data to compress as it will > totally cripple performance. This allocation of buffers is a standard > part of the crypto and jffs2 compression APIs too. >
This is why there are no wrappers for this LZO -- in compressed caching also we have wrappers that take care of this. I don't think anyone will want to alloc/free for every compression they do. So I am just going to leave code without wrappers.
> > I just read the follow-ups to this, so perhaps we /can/ use the unsafe > > versions in certain situations. But I agree with Michael's suggestion > > to rename _safe to decompress and decompress to _unsafe ... > > Lets just add the _unsafe postfix and leave "safe" alone, then it > remains the same name as userspace and will be less confusing for anyone > used to the userspace library ;-).
Ok - will do this :)
> > > Hmmm, perhaps you could extract the common stuff between the > > _safe and _unsafe versions out into a separate function and then > > reuse it from _safe and _unsafe wrappers? In any case, this kind > > of Makefile jugglery (even in the master Makefile) just to avoid the > > above doesn't seem quite right ... > > FWIW, I don't like the symlink much either. My version of the patch > doesn't do things that way.
You have duplicated decompress code twice! Although this will do away with symlink but I was wondering if a symlink is really that bad!
> > > diff --git a/lib/lzo1x/lzo1x_int.h b/lib/lzo1x/lzo1x_int.h > > > [...] > > > +/* Macros for 'safe' decompression */ > > > +#ifdef LZO1X_DECOMPRESS_SAFE > > > + > > > +#define lzo1x_decompress lzo1x_decompress_safe > > > +#define TEST_IP (ip < ip_end) > > > +#define NEED_IP(x) \ > > > + if ((size_t)(ip_end - ip) < (size_t)(x)) goto input_overrun > > > +#define NEED_OP(x) \ > > > + if ((size_t)(op_end - op) < (size_t)(x)) goto output_overrun > > > +#define TEST_LB(m_pos) \ > > > + if (m_pos < out || m_pos >= op) goto lookbehind_overrun > > > +#define HAVE_TEST_IP > > > +#define HAVE_ANY_OP > > > + > > > +#else /* !LZO1X_DECOMPRESS_SAFE */ > > > + > > > +#define TEST_IP 1 > > > +#define TEST_LB(x) ((void) 0) > > > +#define NEED_IP(x) ((void) 0) > > > +#define NEED_OP(x) ((void) 0) > > > +#undef HAVE_TEST_IP > > > +#undef HAVE_ANY_OP > > > + > > > +#endif /* LZO1X_DECOMPRESS_SAFE */ > > > > ... ugh. Yes, extracting the common stuff between the _safe and _unsafe > > variants in a common low-level __lzo1x_decompress kind of function > > definitely looks doable. The low-level function could simply take an extra > > argument (say, set by the _safe and _unsafe wrappers) that tells it > > whether it is being called as safe or unsafe ... helps us get rid of the > > disruptions to all the Makefiles above and these #ifdef's ugliness ... > > I suspect it will probably damage performance unless the compiler is > very clever and I don't trust compilers that much... >
+1. I looked into Satyam suggestion as above but ...yes, we should not leave everything to compiler. And since all this was suggested just to do away with that symlink, I don't think this splitting work is worth the effort.
> > BTW, it'd be really cool if Richard and yourself could get together and > > pool your energies / efforts to develop a common / same patchset for this. > > (I wonder how different your implementations are, actually, and if there > > are any significant performance disparities, especially.) I really like your > > work, as it clears up the major gripe I had with Richard's patchset -- the > > ugliness (and monstrosity) of it. But he's also worked up the glue code for > > cryptoapi / jffs2 etc for this, so no point duplicating his efforts. > > All I will add is that after the amendment I made, the ugliness in my > patchset is confined to one file now and I still think its the better > approach to take. > > My main concerns with this patch are that: > * from the security point of view its not tried and tested code > * I'm not 100% confident in what Nitin has done with the code from a > buffer overflow/security PoV > * its not tested on many architectures > * the performance implications of the rewrite are unknown >
I agree with your points - there can surely be bugs in my porting work since it involves too many chages. But considering that the port is just ~500 lines, if we can fix it and optimize to get comparable/better perf. results than original one, we will end up with much cleaner and smaller code.
For rigous testing, I have sent 'compress-test' module (with usage) to Bret Towe who has 64-bit machines available for testing.
> In theory both sets of code should result in the output bytecode if the > compiler does its job properly. Ideally I'd like to compare the > performance of them as well as have a look at the code. I'm not quite > sure when I'm going to have time for this though :/. > > Also, I did notice you had the error defines in two header files. They > should only exist in one place and the LZO implementation should be > including the copy in linux/. >
Ah! I now notice them -- will keep the copy in linux/lzo1x.h only.
Thanks for your comments.
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