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KERNELD

Section: Linux Extensions (8)
Updated: May 14, 1995
Index

NAME

kerneld - perform kernel action in user space (such as on-demand loading of modules)

SYNOPSIS

kerneld[ debug ] [ keep ] [ delay=<seconds> ] [ type=<message number> ]

DESCRIPTION

Apart from automatically removing unused modules,kerneldalso performs specific kernel tasks in user space by responding to requestsfrom the kernel via a dedicated IPC message queue.Access to this queue can be made from user space by opening the queuewith:

qid = msgget(IPC_PRIVATE, 0600 | IPC_KERNELD);

A specific task is requested with the message type,as specified in <linux/kerneld.h>.

The structure of a kerneld message is:

        struct kerneld_msg {                long mtype;                long id;                char text[1];        };

where the id field is used as the number of the response messagefrom kerneld back to the kernel.If the id field is zero, there will be no response from kerneld.
(Note that a new structure is proposed that will include the pid ofthe requestor into the protocol header.)

If a response was requested, the exit status of the kerneld actionwill be stored in the id field.

The text field us used to hold the parameters from the kernelto the specified kerneld action.In return messages, this field can contain the output from the action,to be used (if wanted) by the kernel.

The options are as follows:

debug: Whith debugging enabled, you will be able to see the current statusof kerneld as it performs its tasks. Note that you can controldebugging, as well as all the other parameters via the utility kdstat.
keep: The keep option makes kerneld ignore all requests for unloading modules.This option might be usable for systems where the modules should neverbe unloaded at all (for some reason or other).This option also inhibits the automatic removal of unused modulesthat kerneld performs every minute (or <delay> seconds).
delay=<seconds>: The delay option will change the timeout in kerneld for delayedremoval of modules from the default 60 seconds to whatever the choice was.
type=<message type>: The default type is -255, which means that kerneld will listen forall messages where the type is less than or equal to 255.If a positive number is given, kerneld will only listen for that message type.

kerneld sends error messages to the syslog facility LOG_DAEMON.

HISTORY

The kerneld support was inspired by discussions with Jacques Gelinas <jackAATTsolucorp.qc.ca>

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