Herbert,
I also wonder, does it at all correct to use negative windowBits in
crypto API? I mean, if windowBits is negative, zlib doesn't produce the
proper zstream header, which is incorrect according to RFC-1950. It also
doesn't calculate adler32.
For example, if we work over an IP network (RFC-2384), the receiving
side may be confused by such a "stripped" zstream.
Isn't it conceptually right to produce *correct* zstream, with the
header and the proper adler32 ?
Yes, for JFFS2 we would like to have no adler32, we anyway protect our
data by CRC32. But I suppose this should be an additional feature.
Comments?
Herbert Xu wrote:
I made the changes to deflate_decompr() because the old version doesn't
work properly for me. There are 2 changes.
1. I've added the following code:
------------------------------------------------------------------------
if (slen > 2 && !(src[1] & PRESET_DICT) /* No preset dictionary */
&& ((src[0] & 0x0f) == Z_DEFLATED) /* Comp. method byte is OK */
&& !(((src[0] << 8) + src[1]) % 31)) { /* CMF*256 + FLG */
stream->next_in += 2;
stream->avail_in -= 2;
}
------------------------------------------------------------------------
The reason you need to add this is because the window bits that
was used to produce the compressed data is positive while the window
bits crypto/deflate is using to perform the decompression isn't.
So what we should do here is turn window bits into a configurable
parameter.
Once you supply the correct window bits information, the above is
then simply an optimisation.
Rather than keeping the above optimisation, JFFS should simply do
the compression with a negative window bits value.
Of course to maintain backwards compatibility you'll need to do this
as a new compression type.
--
Best Regards,
Artem B. Bityuckiy,
St.-Petersburg, Russia.
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