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Diffstat (limited to 'udev-config/doc/60-persistent-input.txt')
-rw-r--r-- | udev-config/doc/60-persistent-input.txt | 86 |
1 files changed, 0 insertions, 86 deletions
diff --git a/udev-config/doc/60-persistent-input.txt b/udev-config/doc/60-persistent-input.txt deleted file mode 100644 index 45030723f..000000000 --- a/udev-config/doc/60-persistent-input.txt +++ /dev/null @@ -1,86 +0,0 @@ -Purpose of rules file: - -This rules file provides nonvolatile, unique names (in the form of symlinks) -for input devices that cooperate. - - -Description of rules: - -This file starts off with a few rules that make Udev skip the entire file if -the current uevent is not input related. If ACTION is not "add", or SUBSYSTEM -is not "input", or KERNEL (the device node) matches "input[0-9]*", then Udev -will GOTO the LABEL named "persistent_input_end", which is the last rule in -this file. (input[0-9]* uevents are skipped because they do not create device -nodes.) - -This type of "skip this list of rules if X" operation is done in both the -persistent input and persistent storage rules files. The reason is efficiency --- if Udev had to go run the usb_id and/or path_id programs for non-input and -non-storage rules, those rules would take much longer to process for no good -reason. - - -First in this file is a set of rules for by-ID style symlinks. These attempt -to uniquely identify a device based on its serial number, but there are some -issues with this. Many USB manufacturers do not provide a unique serial number -for each device -- for instance, my Microsoft Intellimouse Optical has a USB -serial number of "Microsoft_Microsoft_IntelliMouse_Optical". This kind of -nonsensical "serial number" means that if you plug in two Intellimouse Optical -devices, they will both get the same by-id symlink, and the device that the -symlink points to will be random. This defeats the purpose of by-ID symlinks. -(However, I believe this behavior is technically valid according to the USB -standard. I believe it is not recommended, though.) - -Anyway, first in the by-ID rules, we have a rule that runs for any (input) -device hanging anywhere off a USB bus. It uses the IMPORT{program} option to -run the "/lib/udev/usb_id -x" program. usb_id looks at the environment to find -out which device to look at, generates a list of environment-variable VAR=value -pairs, and prints them. Udev stores this output away while the process is -running. After the process exits, Udev modifies the current environment to -include the VARs that usb_id printed. (It assigns the "value"s that usb_id -printed to each of those VARs.) Specifically, usb_id prints ID_VENDOR, -ID_MODEL, ID_REVISION, ID_SERIAL, ID_TYPE, and ID_BUS (at least in the case of -the aforementioned USB optical mouse). These variable names will all be set in -the environment. - -Then, we have a set of rules to set ID_CLASS for various types of devices. The -rules first check for a "usb"-bus device that has a "bInterfaceClass" of 03 and -a "bInterfaceProtocol" of 01. If the interface class is 03, this is an HID -device. If the protocol is 01, it's a keyboard device. So we set ID_CLASS to -"kbd". The next rule checks whether the interface protocol is 02, and if so, -sets ID_CLASS to "mouse" (HID devices with a protocol of 02 are mice). - -Any input device that the "pcspkr" driver claims must be a speaker. Any input -device that the "atkbd" driver claims must be a keyboard. Any input device -that the "psmouse" driver claims must be a mouse. If there's a sysfs attribute -named "name", whose contents contain "dvb", "DVB", or " IR ", then we set -ID_CLASS to "ir". - -Then, we have a rule to search the tree and find the first parent that has a -modalias. If that modalias matches the big long ugly string in the rules file, -we assume this is a joystick device, and set ID_CLASS appropriately. (This -parent should be the kobject for the joystick device itself. The reason we -search the tree is that the current uevent is for a device node, not the -physical joystick device.) - -Once the ID_CLASS variable is set properly, we have one more modification to -perform: if the ID_SERIAL variable was not set at all by the usb_id program, we -set it to "noserial". - -Now that all the environment variables are set up properly, we start generating -the by-ID symlinks in /dev/input/by-id/. If the current device node's name -starts with "event", we add "event" into the symlink name. Otherwise, we don't -add anything for mice. (Other device types don't get a persistent by-ID -symlink.) - - -Next, we create by-path symlinks. The /lib/udev/path_id program takes the path -of the device as an argument, and prints out "ID_PATH=string", where "string" -is the "shortest physical path" to the device. We import this value into the -environment. - -If the path is non-empty, and the device node name starts with "mouse" or -"event", we add a by-path symlink based on the path and the device class (and -we also add "event" if it's an event device). This symlink should be stable as -long as the device never moves to a different port. - |