On 5/12/06, Rajat Jain <rajat.noida.india@xxxxxxxxx> wrote:
thanks Rajat for the idea
but if your application is interested in knowing the error happened then you've to make the call back application write some value somewhere and lets your application read it .. or you have to go IPC
this solution might help for cases where a certain user job must be executed when a certain kernel event happens like for hot plug .. but IMO it's not a good communication model for error checking cases
hope this helps
On 5/11/06, Christian Boon <c.boon@xxxxxxxxxxxxxxxxxxxx> wrote:
> Hi,
>
> i know it is possible with an ioctl to change a value in a kernel module.
> Is it possible to let a kernel module change a value in user space when
> some kind of error occurs?
> so that i dont need to check 'if' an error occured.
>
> Christian.
>
Hi,
Checkout the function "call_usermodehelper" in kmod.c.
/**
* call_usermodehelper - start a usermode application
* @path: pathname for the application
* @argv: null-terminated argument list
* @envp: null-terminated environment list
* @wait: wait for the application to finish and return status.
*
* Runs a user-space application. The application is started
* asynchronously if wait is not set, and runs as a child of keventd.
* (ie. it runs with full root capabilities).
*
* Must be called from process context. Returns a negative error code
* if program was not execed successfully, or 0.
*/
int call_usermodehelper(char *path, char **argv, char **envp, int wait)
This function can be used to call a user space application from
kernel. So kernel won't be actually calling a "call back function" but
a "call back application". However, you can write this application to
perform whatever you want to do.
thanks Rajat for the idea
but if your application is interested in knowing the error happened then you've to make the call back application write some value somewhere and lets your application read it .. or you have to go IPC
this solution might help for cases where a certain user job must be executed when a certain kernel event happens like for hot plug .. but IMO it's not a good communication model for error checking cases
hope this helps
(This mechanism is actually used to call hot plug agent scripts when a
hot-plug event is detected by the kernel).
Hope that helps,
Rajat
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