Re: DEVFS_FS

[Mike Waychison <Michael.Waychison@Sun.COM>]

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Jamie Lokier wrote:
> Mike Waychison wrote:
>>In fact, the opposite is true: userspace should not care at all about
>>major/minor.  Userspace should care about the semantics of the available
>>device nodes available in /dev.  With hardware, I want to _see_ the
>>device nodes created when I _add_ hardware.  udev handles this semantic
>>very well.  Where it fails is solely in the added devfs semantic of
>>modprobing on lookups of non-existing device nodes.  _This_ is the case
>>where some form of trapping would help very much.
> 
> 
> I agree, this is desirable behaviour.  But it isn't perfect.
> 
> Better than trapping would be if /dev/net/tun0 and so forth did
> actually exist in /dev, to indicate the availability of those devices,
> but the modules were still autoloaded on first access.

That would be cool. :)

> 
> It would also be nicer if the device nodes were created to indicate
> available/installed devices, without actually initialising the devices
> or loading the bulk of their driver until they're needed.
> 
> In other words, if /dev were auto-generated based on all available
> hardware and all available non-hardware drivers for the current
> kernel, including modules not yet loaded.
> 
> That would be better IMNSHO, to the extent that it's possible.
> 
> Although it's necessary to load drivers for some devices (like ISA
> cards) to detect them, it isn't necessary to load PCI drivers to
> detect that they are present.  A mapping directly from detected PCI
> ids to whatever udev needs could be extracted from the drivers at
> compile time.  Such mappings nearly exist now, except that the mapping
> is from ids to drivers, instead of ids to dev info.

The problem is that you do need to load the drivers for devices to see
any attached hardware.

For instance, consider the case where you boot of ide, but have an
attached scsi card.  There is no way for you to know what is behind that
scsi card until you load the drivers :(

- --
Mike Waychison
Sun Microsystems, Inc.
1 (650) 352-5299 voice
1 (416) 202-8336 voice

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