[linux-dvb] Re: Linux DVB API 4 Q's

[Johannes Stezenbach <js@convergence.de>]

Rob.McConnell@Zarlink.Com wrote:
> 
> 1)  DVB_DMX_START and DVB_DMX_STOP ioctls will globally work on any filters
> attached to a single fd.  I guess the advantage of keeping the DVB_DMX_STOP
> ioctl is to reduce any time required to do an "open" on a new fd after you
> did a "close".
> 
> 2) To individually ADD & START a filter issue the DVB_DMX_ADD_PID_FILTER
> ioctl with the DVB_DMX_IMMEDIATE_START flag set.
> 
> 3) To START a group of filters at once, issue the DVB_DMX_START ioctl on
> the required fd.
> 
> 4) To STOP a group of filters (e.g. pausing), issue the DVB_DMX_STOP ioctl
> on the required fd.
> 
> 5) To individually STOP and remove a filter issue the
> DVB_DMX_DEL_PID_FILTER ioctl.
> 
> 
> OK, does this look reasonable?

Maybe it's just a matter of taste, but I think that sucks :-(

o at open() time we don't know what the user is going to do with the
  new file descriptor, hence there isn't much overhead in open() /
  close(); all the work is in starting and stopping the filters
o state handling in the driver *and* in the application will be more
  complicated when we have to deal with filters which are set but not
  started
o if you want to start a number of filters at once, you might also
  want to stop then together (symmetry)


I would prefer to:

- pass an array of PIDs to ADD/DEL
- remove the DVB_DMX_IMMEDIATE_START, DVB_DMX_START and DVB_DMX_STOP ioctls

While I don't think that it's important for me to set a number of
filters at exactly the same time, this would simplify error handling
because we can make setting all filters together either succeed or fail
(atomicity).

I think this a simple and efficient API. Don't you?


Johannes


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