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Diffstat (limited to 'udev-config/doc/80-drivers.txt')
| -rw-r--r-- | udev-config/doc/80-drivers.txt | 69 |
1 files changed, 0 insertions, 69 deletions
diff --git a/udev-config/doc/80-drivers.txt b/udev-config/doc/80-drivers.txt deleted file mode 100644 index e5cfcefb3..000000000 --- a/udev-config/doc/80-drivers.txt +++ /dev/null @@ -1,69 +0,0 @@ -Purpose of rules file: - -The rules in this file allow Udev to fully replace the old /sbin/hotplug -script. They automatically load kernel modules as devices are discovered. - - -Description of rules: - -All rules in this file match ACTION=="add", so they only run when devices are -being added. - -ENV{MODALIAS} is the value of the environment variable named MODALIAS. This -environment variable is sent by the kernel when it sends a uevent for any -device that has a modalias. Modaliases are strings that can be used to load -the appropriate kernel module driver. - -Generally a modalias will contain information like vendor ID, device ID, and -possibly other IDs depending on the bus the device is connected to. (USB, for -instance, has the concept of a "device class" and a "device interface", which -are basically just ways to standardize the USB protocol for various types of -devices. This is what allows a single kernel module such as hid.ko to drive -many different vendors' USB input devices: all devices that support the USB -HID interface expose the HID interface number in their modalias, and so the -hid.ko driver can be loaded for each device. When it loads, hid.ko attaches -to the HID interface and does whatever is needed to work with each device.) - -Kernel modules that drive hardware expose a list of modaliases. These -modaliases are matched against the device modalias by /sbin/modprobe (after -shell-style expansion), with the help of /sbin/depmod's modules.alias file. -The upshot of all this is, you can tell Udev to run "/sbin/modprobe modalias", -and it will load the module that claims it can drive the "modalias" device. - -The rule that does this inspects ENV{MODALIAS} to ensure it is not empty. It -does this by comparing it to "?*" -- inside a match, "*" would match *any* -string, including the empty string, so to ensure MODALIAS is not empty, we need -to match against "?*" instead. ("?" matches any one character.) - -The Udev RUN+="" option adds a program to run when the rule matches. In this -case, we tell Udev to run "/sbin/modprobe $env{MODALIAS}". Note that Udev does -not do path searches; if the executable is not specified with a fully-qualified -path, it *must* be located under the /lib/udev directory. If it is not, you -*must* specify a fully-qualified path, as we do here. Also, "$env{string}" is -replaced by the value of the environment variable "string" when the command -runs, so this adds the modalias to the modprobe command. The modprobe program -will do the rest. Finally, the {ignore_error} option is added to the RUN key; -this prevents Udev from failing the uevent if the modprobe command fails. (The -modprobe command will fail when run during cold-plugging, if the driver was -configured into the kernel instead of as a module, for instance.) - -There is still one feature of the old hotplug shell-script system that Udev -cannot provide: blacklisting modules from being auto-loaded. To accomplish -this, we must use module-init-tools. In /etc/modprobe.conf, if you use the -"blacklist <module-name>" syntax, modprobe will not load <module-name> under -any name except its real module name. Any modaliases exposed by that module -will not be honored. - - -There are also rules in this file for various other types of driver loading. -PNP-BIOS devices, for instance, expose a list of PNP IDs in their sysfs "id" -attribute, instead of exposing a single MODALIAS, so one rule loops through -each ID and tries to load the appropriate module. Several other types of -devices require an extra module before they will work properly; one example -of this is IDE tapes, which require the ide-scsi module. Finally, whenever -any SCSI device is found, the file uses the TEST key to check whether the -/sys/module/sg directory exists. If not, then the "sg" module -- the SCSI -generic driver -- is loaded. (That driver creates the module/sg directory, -so the module/sg test is just to see whether the driver has already been -loaded.) - |