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1c4800743d
Updated Makefile to automatically generate bootscript and udev-config tarballs Updated licesnse to be the same as BLFS git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@8548 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689
87 lines
4.5 KiB
Plaintext
87 lines
4.5 KiB
Plaintext
Purpose of rules file:
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This rules file provides nonvolatile, unique names (in the form of symlinks)
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for input devices that cooperate.
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Description of rules:
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This file starts off with a few rules that make Udev skip the entire file if
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the current uevent is not input related. If ACTION is not "add", or SUBSYSTEM
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is not "input", or KERNEL (the device node) matches "input[0-9]*", then Udev
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will GOTO the LABEL named "persistent_input_end", which is the last rule in
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this file. (input[0-9]* uevents are skipped because they do not create device
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nodes.)
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This type of "skip this list of rules if X" operation is done in both the
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persistent input and persistent storage rules files. The reason is efficiency
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-- if Udev had to go run the usb_id and/or path_id programs for non-input and
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non-storage rules, those rules would take much longer to process for no good
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reason.
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First in this file is a set of rules for by-ID style symlinks. These attempt
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to uniquely identify a device based on its serial number, but there are some
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issues with this. Many USB manufacturers do not provide a unique serial number
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for each device -- for instance, my Microsoft Intellimouse Optical has a USB
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serial number of "Microsoft_Microsoft_IntelliMouse_Optical". This kind of
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nonsensical "serial number" means that if you plug in two Intellimouse Optical
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devices, they will both get the same by-id symlink, and the device that the
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symlink points to will be random. This defeats the purpose of by-ID symlinks.
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(However, I believe this behavior is technically valid according to the USB
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standard. I believe it is not recommended, though.)
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Anyway, first in the by-ID rules, we have a rule that runs for any (input)
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device hanging anywhere off a USB bus. It uses the IMPORT{program} option to
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run the "/lib/udev/usb_id -x" program. usb_id looks at the environment to find
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out which device to look at, generates a list of environment-variable VAR=value
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pairs, and prints them. Udev stores this output away while the process is
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running. After the process exits, Udev modifies the current environment to
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include the VARs that usb_id printed. (It assigns the "value"s that usb_id
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printed to each of those VARs.) Specifically, usb_id prints ID_VENDOR,
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ID_MODEL, ID_REVISION, ID_SERIAL, ID_TYPE, and ID_BUS (at least in the case of
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the aforementioned USB optical mouse). These variable names will all be set in
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the environment.
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Then, we have a set of rules to set ID_CLASS for various types of devices. The
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rules first check for a "usb"-bus device that has a "bInterfaceClass" of 03 and
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a "bInterfaceProtocol" of 01. If the interface class is 03, this is an HID
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device. If the protocol is 01, it's a keyboard device. So we set ID_CLASS to
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"kbd". The next rule checks whether the interface protocol is 02, and if so,
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sets ID_CLASS to "mouse" (HID devices with a protocol of 02 are mice).
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Any input device that the "pcspkr" driver claims must be a speaker. Any input
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device that the "atkbd" driver claims must be a keyboard. Any input device
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that the "psmouse" driver claims must be a mouse. If there's a sysfs attribute
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named "name", whose contents contain "dvb", "DVB", or " IR ", then we set
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ID_CLASS to "ir".
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Then, we have a rule to search the tree and find the first parent that has a
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modalias. If that modalias matches the big long ugly string in the rules file,
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we assume this is a joystick device, and set ID_CLASS appropriately. (This
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parent should be the kobject for the joystick device itself. The reason we
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search the tree is that the current uevent is for a device node, not the
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physical joystick device.)
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Once the ID_CLASS variable is set properly, we have one more modification to
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perform: if the ID_SERIAL variable was not set at all by the usb_id program, we
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set it to "noserial".
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Now that all the environment variables are set up properly, we start generating
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the by-ID symlinks in /dev/input/by-id/. If the current device node's name
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starts with "event", we add "event" into the symlink name. Otherwise, we don't
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add anything for mice. (Other device types don't get a persistent by-ID
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symlink.)
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Next, we create by-path symlinks. The /lib/udev/path_id program takes the path
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of the device as an argument, and prints out "ID_PATH=string", where "string"
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is the "shortest physical path" to the device. We import this value into the
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environment.
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If the path is non-empty, and the device node name starts with "mouse" or
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"event", we add a by-path symlink based on the path and the device class (and
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we also add "event" if it's an event device). This symlink should be stable as
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long as the device never moves to a different port.
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