Hi Mark,
On 5/30/07, Mark Adler <[email protected]> wrote:
On May 29, 2007, at 8:15 AM, Satyam Sharma wrote:
> skipping some checksum calculation if some
> flag (PRESET_DICT) is absent from the input stream about to
> be decompressed ...
You don't need to dissect the header manually to look for that bit.
If you feed inflate() at least the first two bytes, it will return
immediately with the Z_NEED_DICT return code if a preset dictionary
is requested. You can force inflate() to return immediately after
decoding the two byte header even if a preset dictionary is not
requested by using the Z_BLOCK flush code.
Thanks for replying, unfortunately I don't know either zlib or jffs2 code
deeply enough to actually understand what you meant here. Are you
saying that the if-else block in question [1] in
fs/jffs2/compr_zlib.c:jffs2_zlib_decompress() is unnecessary and can
be done away with?
Thanks,
Satyam
[1] For your reference, here is the user code in question:
inf_strm.next_in = data_in;
inf_strm.avail_in = srclen;
inf_strm.total_in = 0;
inf_strm.next_out = cpage_out;
inf_strm.avail_out = destlen;
inf_strm.total_out = 0;
int wbits = MAX_WBITS;
/* If it's deflate, and it's got no preset dictionary, then
we can tell zlib to skip the adler32 check. */
if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
((data_in[0] & 0x0f) == Z_DEFLATED) &&
!(((data_in[0]<<8) + data_in[1]) % 31)) {
D2(printk(KERN_DEBUG "inflate skipping adler32\n"));
wbits = -((data_in[0] >> 4) + 8);
inf_strm.next_in += 2;
inf_strm.avail_in -= 2;
} else {
/* Let this remain D1 for now -- it should never happen */
D1(printk(KERN_DEBUG "inflate not skipping adler32\n"));
}
if (zlib_inflateInit2(&inf_strm, wbits) != Z_OK) {
printk(KERN_WARNING "inflateInit failed\n");
return 1;
}
while((ret = zlib_inflate(&inf_strm, Z_FINISH)) == Z_OK)
;
if (ret != Z_STREAM_END)
printk(KERN_NOTICE "inflate returned %d\n", ret);
zlib_inflateEnd(&inf_strm);
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