[linux-dvb] Re: More than 4 DVB cards - again

[Michael Hunold <hunold@convergence.de>]

Hello Irek,

On 06/25/04 08:56, Irek Defee wrote:
> It is strange that this issue has been downgraded comparing to kernel
> 2.4. For me it’s a huge factor not to upgrade to 2.6:). 
The "problem" is that devfs in 2.4 has the "feature" that a device node 
is not tightly coupled to a major/minor pair. So if you select 
devfs-only support for DVB, then you can register as many adapters as 
you want.

This feature of devfs has been considered to be broken, so in 2.6 this 
has been removed. Because of this, we now only have 1 major and 256 
minor numbers, limiting the number of DVB adapters with our current 
numbering scheme to 4 adapters.

So this is not the fault of the DVB developers.

> But I would suggest to developers to  take this into account and provide
> direct plug-and-play support for more than 4 cards. 6 PCI slots is the
> maximum amount in PC motherboards which also have on-board network
> adapter. Thus, it is natural to think that high-end installations
> may include 6 cards. Then, there are also more exotic server boards
> with several PCI buses and they could take more than 6 cards which
> could also be considered.    
There are several possible solutions:
1) dev_t in 2.6 has now 32 bit (12 bit for the major and 20 bit for the 
minor number). See http://lwn.net/Articles/49684/. If we use this, users 
need to have an up-to-date glibc probably, at least they need a new 
mknod to create the device nodes properly.
2) Re-organize the device numbering, so that more adapters fit into 256 
minor numbers. This would require non-devfs users to re-create their 
device nodes and would probably confuse many users.
3) Allocate another major number and handle adapters 5-8 there.

I'd vote for solution 3 -- patches are welcome. 8-)

CU
Michael.