Block a physical property?

[Kay Sievers]

On Wed, Aug 24, 2005 at 01:40:40PM -0400, David Zeuthen wrote:
> 
> Hi,
> 
> Sorry for the lag,
> 
> Pierre Ossman wrote:
> >Pierre Ossman wrote:
> >
> >>How come 'block' is considered a physical property (a bus even) and not
> >>a functional property? It seems a bit weird from my point of view. That
> >>something is block based seems more of a protocol detail than anything 
> >>else.
> >>
> >>I know the sysfs layout is a but funky concerning block devices, but the
> >>concensus seem to be that it should be eventually moved to 
> >>/sys/class/block.
> 
> No, this will never change (see archives on linux-hotplug for greg kh 
> and kay (both udev maintainers) saying this) because it's a change that 
> will gain us nothing and only break existing user space...

That may happen some day, if we get stacked class-devices in /sys/class,
but sure, /sys/class/block/ is far away from now, cause a whole lot of
userspace including udev is not prepared to handle anything like that at the
moment.

> >>Also, the block "bus" forgets to set info.bus. ;)
> >
> It's not a bus at all.. it's just properties on device objects.. but see 
>  below.
> 
> >After sleeping on it, I started wondering why we have this namespace at
> >all. Wouldn't it be better to move block.device into storage? And
> >major/minor seems a bit linux specific. So it should probably be under
> >the linux namespace.
> 
> I don't think major/minor is Linux specific. I believe it is POSIX.

At least block.device and major minor at the same level sound sane to me
too. But why is a printer "linux.device_file", sound "alsa.device_file" and
storage "block.device"? :)

> >Besides, if we have a block namespace, why don't we have a char namespace?
> >
> What would be the point?

Char namespace does not make sense. If you are interested, read the
long discussion about "/sys/char" in the kernel...

> >I also noticed that all functional nodes in the HAL tree were missing
> >info.bus. Could cause some trouble since the spec says it's mandatory. I
> >suppose they should inherit it from their parent. Which would make
> >storage.bus obsolete (provided that block goes the way of the dodo).
> 
> storage.bus is just shorthand for looking at info.bus at the hal device 
> object with the udi referenced in storage.physical_device.

Btw: In the spec info.bus is mandatory but not all devices have it. We should
correct HAL or the spec here.

Thanks,
Kay