[linux-dvb] Re: [PATCH] section demux rewritten

[Ralph Metzler <rjkm@metzlerbros.de>]

Emard writes:
 > Wise desision, i will test it further, also I'd like to put to_right_place
 > the #define MAX_SECBUFP 4096 or 16384, instead of having 
 > secbuf_real[4096 or 16384]
 > 
 > > >+        u8 *secbuf;
 > > >+        u8 secbuf_real[16384];
 > 
 > directy in the struct. Although we know the individual section is 
 > max 4096 bytes, I would like to be able to easily increase 2-4 
 > times that buffer in case the transmission equipment goes amok and 
 > builds some larger chunks
 > without PUSI, to still avoid loosing some section data. 
 > (in few tests so far I haven't seen building them over 4096 but..)

If that really happens (doubt it) they are sending a broken stream.
Your truncate_copy prevents access to more than 4096 bytes anyway.

I don't understand several other things in your code:

- unnecessary pointer juggling (when is secbuf ever not finally reset to
  secbuf_real in the dump routine?)

- probably timing problems with low bandwidth PIDs with long (>183
  bytes) sections (think about when dump is called in this case)

- thrown away CC checking
  of course it it not foolproof (e.g. if you miss exactly 16 packets of one PID)
  but at least it can show minor dropouts and reject this data.

The only advantage (less copying with small sections in same packet)
is trivial to add to the old code.


Ralph  



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