Re: [RFC] CryptoAPI & Compression

[Artem B. Bityuckiy]

David Woodhouse wrote:
> On Fri, 2005-04-01 at 18:57 +0400, Artem B. Bityuckiy wrote:
> 
>>Yes, the compression will be better. But the implementation will be more 
>>complicated.
>>We can try to use the "bound" functions to predict how many bytes to 
>>pass to the deflate's input, but there is no guarantee they'll fit into 
>>the output buffer. In this case we'll need to try again.
> 
> 
> Can we not predict the maximum number of bytes it'll take to flush the
> stream when we're not using Z_SYNC_FLUSH?

AFAIU, no. Zlib may eat a lot of input and do not produce much output, but 
on Z_FINISH it may ask an undetermined amount of additional output space. 
So, we must even regulate the amount of input we pass to zlib_deflate(). 
In case of Z_SYNC_FLUSH, things are more determined.

Another question, does JFFSx *really* need the peaces of a 4K page to be 
independently uncompressable? It it wouldn't be required, we would achieve 
better compression if we have saved the zstream state. :-) But it is too 
late to change things at least for JFFS2.

--
Best Regards,
Artem B. Bityuckiy,
St.-Petersburg, Russia.
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