[linux-dvb] Re: EOVERFLOW with section filter

[Gerard MAULINO <gmaulino@club-internet.fr>]

Johannes Stezenbach wrote:

> On Tue, Jan 14, 2003 at 03:49:36PM +0100, Felix Domke wrote:
>  
> > Johannes Stezenbach wrote:
> >
> >    
> > > Regardless what manual pages or POSIX say, the driver implements
> > > read() for section filters in such a way that you get either
> > > a full section, or nothing -- provided that the buffer you pass
> > > to read() is large enough for the section (else you will get
> > > partial sections, but never the end of one section and the start
> > > of the next section in one read).
> > >
> > >      
> > Sorry, I think after a partitial section you read the same section 
> > again, since otherwise the "read 3 bytes, determine length, read whole 
> > section"-sheme wouldn't work.  And exactly this leeds to EOVERFLOW, 
> > since the buffer fills and fills and no section will ever be removed 
> > from the buffer.
> >    
> If this is true then it is a bug. The second read() should give
> you the remainder of the section, and the section should then
> be removed from the driver's buffer.
>
> DVB/doc/dvbapi/demux.tex documents this behaviour of the
> read() system call for section filters.
>
> But I must admit that I haven't tested this, I always use a large
> buffer and get full sections.
>
>
> Regards,
> Johannes
>
>
>  
Hi,

I use a program that do that (ie:  read 3 bytes, then read the rest of 
the section). It works for me and it has the advantage to work with the 
"world" of reading section. I mean reading from a file or a socket. I 
don't know what's the better way to implement this, but I know that most 
of data sections in the french air are less than 4kb and also than 1kb 
(BAT, EIT, SDT...). So if you need to get about ten megas of data cutted 
in sections of 2kb you will probably lost time and space using a read of 
4k's buffer.

Regards

Gerard



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