[linux-dvb] [PATCH] Bug in section filtering (and fix)

Mark Adams mark147m at gmail.com
Mon Oct 24 17:38:54 CEST 2005


> It sounds quite logical.. It wouldn't break anything too. Probably the
> best to test this patch would be on lowbitrate streams on satellites
> like Hotbird .. ;-) It shouldn't make any difference otherwise. My
> antenna which was pointing at Hotbird, went down in a wind a while back,
> and i haven't replaced it yet.

The case that provokes the problem is where a PID carrying section
data contains both small sections, less than a TS packet in size, and
large sections, very close to the maximum 4096 bytes.

This can arise in DSMCC carousels, in EIT schedule data (EPG
information) and anywhere else where there are sections of various
sizes.

The bitrate of the stream is of no consequence: the data loss caused
by the bug will be the same.

Since DSMCC and EIT data is broadcast repetitively, there is a good
chance that the section lost by this bug will be found on a subsequent
repetition.  However, this is not guaranteed because in some (many?)
cases, the pattern of the sections in the stream will be the same at
the next repetition and the bug will strike each time.

The situation that prompted me to investigate and propose the patch
was a DSMCC carousel in which I found I _never_ received a particular
file that I knew was present.

Mark



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