mirror of
https://github.com/AuxXxilium/eudev.git
synced 2024-12-15 19:16:08 +07:00
97 lines
4.0 KiB
Plaintext
97 lines
4.0 KiB
Plaintext
|
|
We've got a couple goals for udev:
|
|
|
|
1) dynamic replacement for /dev
|
|
2) device naming
|
|
3) API to access info about current system devices
|
|
|
|
Splitting these goals into separate subsystems:
|
|
|
|
1) udev - dynamic replacement for /dev
|
|
2) namedev - device naming
|
|
3) libsysfs - a standard library for accessing device information on the
|
|
system.
|
|
|
|
Udev
|
|
------
|
|
|
|
Udev will be responsible for responding to /sbin/hotplug on device
|
|
events. It will receive the device class information along with
|
|
device's sysfs directory. Udev will call the name_device function from
|
|
the naming device subsystem with that information and receive a unique
|
|
device name in return. Udev will then query sysfs through the libsysfs
|
|
for specific device information required for creating the /dev node like
|
|
major and minor number. Once it has the important information, udev
|
|
will create a /dev entry for the device, add the device to the in memory
|
|
table of current devices, and send notification of the successful event
|
|
through a D-BUS message. On a remove call, udev will remove the /dev
|
|
entry, remove the device from the in memory table, and send
|
|
notification.
|
|
|
|
Udev will consist of a command udev - to be called from /sbin/hotplug.
|
|
It will require the in memory dynamic database/table for keeping track
|
|
of current system devices, and a library of routines for accessing that
|
|
database/table. Udev will not care about "how" devices are named, that
|
|
will be separated into the device naming subsystem. It's presented a
|
|
common device naming API by the device naming subsystem to use for
|
|
naming devices.
|
|
|
|
|
|
|
|
namedev
|
|
----------
|
|
|
|
From comments people have made, the device naming part of udev has been
|
|
pushed into its own "subsystem". The reason is to make this as flexible
|
|
and pluggable as possible. The device naming subsystem, or namedev, will
|
|
present a standard interface for udev to call for naming a particular
|
|
device. Under that interface, system administrators can plug in their
|
|
own methods for device naming.
|
|
|
|
We would provide a default naming scheme. The first prototype
|
|
implementation could simply take the sysfs directory passed in with the
|
|
device name function, query sysfs for the major and minor numbers, and
|
|
then look up in a static device name mapping file the name of the
|
|
device. The static device naming file could look just like devices.txt
|
|
in the Linux kernel's Documentation directory. Obviously, this isn't a
|
|
great implementation because eventually we'd like major an minor numbers
|
|
to be dynamic.
|
|
|
|
The default naming scheme in the future would have a set of policies to
|
|
go through in order to determine the name of the device. The device
|
|
naming subsystem would get the sysfs directory of the to be named device
|
|
and would use the following information in order to map the device's
|
|
name:
|
|
|
|
1) Label info - like SCSI's UUID
|
|
2) Bus Device Number
|
|
3) Topology on Bus
|
|
4) Kernel Name - DEFAULT
|
|
|
|
System administrators could use the default naming system or enterprise
|
|
computing environments could plug in their Universal Unique Identifier
|
|
(UUID) policies. The idea is to make the device naming as flexible and
|
|
pluggable as possible.
|
|
|
|
The device naming subsystem would require accessing sysfs for device
|
|
information. It will receive the device's sysfs directory in the call
|
|
from udev and use it to get more information to determine naming. The
|
|
namedev subsystem will include a standard naming API for udev to use.
|
|
The default naming scheme will include a set of functions and a static
|
|
device naming file, which will reside in /etc or /var.
|
|
|
|
|
|
|
|
libsysfs
|
|
--------
|
|
|
|
There is a need for a common API to access device information in sysfs.
|
|
The device naming subsystem and the udev subsystem need to take the
|
|
sysfs directory path and query device information. Instead of copying
|
|
code so each one will have to readdir, etc., splitting this logic of
|
|
sysfs calls into a separate library that will sit atop sysfs makes more
|
|
sense. Sysfs callbacks aren't standard across devices, so this is
|
|
another reason for creating a common and standard library interface for
|
|
querying device information.
|
|
|