On 5/24/07, Richard Purdie <[email protected]> wrote:
On Thu, 2007-05-24 at 01:04 +0530, Satyam Sharma wrote:
> On 5/23/07, Nitin Gupta <[email protected]> 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.
- Nitin
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
