[linux-dvb] RE : RE : RE : linux-dvb and Dektec [was: DVB API update]

Thierry Lelegard thierry.lelegard at tv-numeric.com
Thu Oct 4 11:36:50 CEST 2007


> Copying in and out of kernel is not fun and eats 
> a lot of your CPU. Which is quite useless.

It is not a matter of performance, it is a matter of
operating system security and stability.

Access to a device is a matter of security, it needs
access to internal kernel structure, it needs user access
control. It must be in the kernel.

Once you gain access to a DBV device, there is no security
involved in demuxing the TS. There is no *need* to implement
a software demux in the kernel.

Concerning stability, the more code you put in the kernel,
the more potential bugs you get. Bugs in the kernel means
potential security breach, potential system hang or crash.
So, when there is no good security reason to put something
the kernel, you don't.

This is what it done in microkernels such as Chorus, Mach or L4.
I know, Linux is a monolithic kernel, not a microkernel.
But monolithic does not mean bloated. See Solaris or OpenVMS,
they are monolithic kernels, but they know when it is reasonable
to put code in the kernel and when it is not.




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