mirror of
https://git.linuxfromscratch.org/lfs.git
synced 2025-01-19 05:27:39 +00:00
34 lines
1.5 KiB
Plaintext
34 lines
1.5 KiB
Plaintext
|
Purpose of rules file:
|
||
|
|
|
||
|
|
The kernel does not always fully populate a given kobject's attributes before
|
||
|
|
sending the uevent for that kobject. This means that a given sysfs directory
|
||
|
|
may not have all the required files in it (each directory corresponds to a
|
||
|
|
kobject, and each file corresponds to an attribute).
|
||
|
|
|
||
|
|
Therefore, we must sometimes wait for attributes to show up when devices are
|
||
|
|
discovered. This is accomplished by udev's WAIT_FOR_SYSFS rule types.
|
||
|
|
|
||
|
|
|
||
|
|
Description of rules:
|
||
|
|
|
||
|
|
All rules in this file match ACTION="add", because none of them apply when
|
||
|
|
devices are being removed.
|
||
|
|
|
||
|
|
SUBSYSTEM is the kernel subsystem that the device uses. Current kernels have
|
||
|
|
some issues with SCSI device attributes being created too late. For any device
|
||
|
|
with a SUBSYSTEM of scsi, we must wait for the ioerr_cnt attribute. (This is
|
||
|
|
the last attribute created for SCSI devices, so when this attribute appears,
|
||
|
|
the kobject is fully populated.)
|
||
|
|
|
||
|
|
It is also possible to use SUBSYSTEMS in Udev rules. Using SUBSYSTEMS would
|
||
|
|
cause Udev to search up the device tree for a matching SUBSYSTEM value. (Note
|
||
|
|
that "the device tree" is not necessarily the same as the path under /sys (the
|
||
|
|
DEVPATH). Rather, "up the device tree" is the path followed by udevinfo when
|
||
|
|
it is given the argument "-a".)
|
||
|
|
|
||
|
|
We do not use SUBSYSTEMS in this rule, because we only care about the SUBSYSTEM
|
||
|
|
of the kobject in question. We don't care about devices that are children of
|
||
|
|
SCSI devices, only the SCSI device itself. We will use SUBSYSTEMS in later
|
||
|
|
rules, though.
|
||
|
|
|