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- 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.
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