Re: libz, libbz2, ramfs and cramfs

[Paul Mackerras <paulus@samba.org>]

I wrote:

> I added a deflateOutputPending routine which returns the number of
> bytes of data that the compressor has pending to give to you.

I just checked and in fact ppp_deflate doesn't use this.

> I added a check so that it is legal to set strm->next_out to NULL and
> the de/compressor will just discard its output data.  This is useful
> on the sending side for PPP-deflate because there are situations where
> the transmitted data has to be added to the compressor's history but
> may not be transmitted in compressed form.

ppp_deflate doesn't use next_out = NULL in this case, but it does use
next_out = NULL when we are compressing a packet and the compressed
packet turns out to be larger than the uncompressed.  With deflate
there is a limit on how much larger the compressed packet would be, so
it would be possible to give it a small extra buffer on the stack
instead of using next_out = NULL.

If we were going to standardize on a newer zlib in the kernel, I could
change ppp_deflate to cope with that without too much pain, I think.
The main thing I would want to add is a way to check what state the
decompressor is in at the end of each packet - we want
strm->state->blocks->mode == LENS at that point, which is not
something that can be checked using the existing zlib interface.

Paul.