| 1 | Purpose of rules file:
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| 2 |
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| 3 | The kernel does not always fully populate a given kobject's attributes before
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| 4 | sending the uevent for that kobject. This means that a given sysfs directory
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| 5 | may not have all the required files in it (each directory corresponds to a
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| 6 | kobject, and each file corresponds to an attribute).
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| 7 |
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| 8 | Therefore, we must sometimes wait for attributes to show up when devices are
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| 9 | discovered. This is accomplished by udev's WAIT_FOR_SYSFS rule types.
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| 10 |
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| 11 |
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| 12 | Description of rules:
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| 13 |
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| 14 | All rules in this file match ACTION="add", because none of them apply when
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| 15 | devices are being removed.
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| 16 |
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| 17 | SUBSYSTEM is the kernel subsystem that the device uses. Current kernels have
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| 18 | some issues with SCSI device attributes being created too late. For any device
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| 19 | with a SUBSYSTEM of scsi, we must wait for the ioerr_cnt attribute. (This is
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| 20 | the last attribute created for SCSI devices, so when this attribute appears,
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| 21 | the kobject is fully populated.)
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| 22 |
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| 23 | It is also possible to use SUBSYSTEMS in Udev rules. Using SUBSYSTEMS would
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| 24 | cause Udev to search up the device tree for a matching SUBSYSTEM value. (Note
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| 25 | that "the device tree" is not necessarily the same as the path under /sys (the
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| 26 | DEVPATH). Rather, "up the device tree" is the path followed by udevinfo when
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| 27 | it is given the argument "-a".)
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| 28 |
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| 29 | We do not use SUBSYSTEMS in this rule, because we only care about the SUBSYSTEM
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| 30 | of the kobject in question. We don't care about devices that are children of
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| 31 | SCSI devices, only the SCSI device itself. We will use SUBSYSTEMS in later
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| 32 | rules, though.
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| 33 |
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