Re: Flaw in the driver-model implementation of attributes

["Kevin P. Fleming" <kpfleming@cox.net>]

Alan Stern wrote:

> For example, on my system the master device on the first PCI IDE channel
> is a hard disk, hda in fact.  This means that
> /sys/devices/pci0/0000:00:07.1/ide0/0.0/ and /sys/block/hda/ refer to the
> same physical device.  One is created by the IDE bus driver, the other by
> a block device driver.  Granted, there are links from one to the other,
> but it still indicates that the organization of sysfs reflects the
> software organization of the kernel as much as the physical organization
> of the computer system.
> 

PMJFI, and I'm not driver model expert, but I can think I can answer 
this one. Yes, you are correct, these two sysfs directories are 
associated with the same physical devices. However, they are definitely 
two different things.

The first is an IDE device. It has attributes common to IDE devices, 
like DMA/PIO mode, cable type, bus speed, etc.

The second is a block device. A _generic_ block device. It has 
attributes like length, dev (its device number), I/O scheduler settings, 
etc.

These are two wildly differing views, but yes, they are the same device. 
These differing attributes do _not_ belong in the same directory. An 
application looking at your IDE devices does not really care how the 
block subsystem perceives those devices (i.e. hdparm). Conversely, an 
application looking at your block devices should not care about what 
underlying physical devices (if any :-) they are associated with.