On 03/07/2011 10:27 AM, Kay Sievers wrote:
The usual enumeration in udev never uses the device tree in
/sys/devices/, only the subsystem lists /sys/{class,bus}/. We could
have something to enumerate all child devices of a given device. It's
not simple, but could be made working.
Hi Kay,
The documentation in Documentation/sysfs-rules.txt seems to warn against
using /sys/class and sys/bus:
- devices are only "devices"
There is no such thing like class-, bus-, physical devices,
interfaces, and such that you can rely on in userspace. Everything is
just simply a "device". Class-, bus-, physical, ... types are just
kernel implementation details which should not be expected by
applications that look for devices in sysfs.
...
- all elements of a devpath must be real directories. Symlinks
pointing to /sys/devices must always be resolved to their real
target and the target path must be used to access the device.
That way the devpath to the device matches the devpath of the
kernel used at event time.
- using or exposing symlink values as elements in a devpath string
is a bug in the application
...
- accessing attributes reached by a symlink pointing to another
device,
like the "device"-link, is a bug in the application
...
- Hierarchy in a single device tree
There is only one valid place in sysfs where hierarchy can be examined
and this is below: /sys/devices.
and more...
I figured that this document was probably out of date, since even
libudev uses /sys/class. What's your take on this document?
Alan.
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