linux-kernel - Re: Signal from kernel space to user space

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Message-ID: <4B1533B0.1030007@compro.net>
Date:	Tue, 01 Dec 2009 10:18:08 -0500
From:	Mark Hounschell <markh@...pro.net>
To:	Clemens Ladisch <clemens@...isch.de>
CC:	Mai Daftedar <mai.daftedar@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: Signal from kernel space to user space

Clemens Ladisch wrote:
> Mai Daftedar wrote:
>>    Im still new to the kernel development world :)and  I was wondering
>> what functions I can use in the kernel space for a signal to be sent
>> to the userspace
> 

I have some interest in this. Might I inject a couple of probably stupid related questions?

> kill_pid_(info) is to be preferred over send_sig_info because it ensures
> that the destination process has the same identity (a plain pid number
> might have wrappend around and be in use by another process).
> 

Does that mean I can't assume my process pid will unique for the life of the process?

> However, why are you using a signal? What information are you trying to
> send, and why wouldn't eventfd or a plain device thaz becomes readable
> be a better solution?
> 

If no "information" is required, which of these are the fastest, say from an interrupt handler?
I have a PCI card that handles external interrupts from the outside world and does nothing but
report those external interrupts to userland. We use send_sig or wake_up_process depending
on whether userland is going to wait for it or not. If there is a better/faster way I would be
very interested.

Thanks and sorry for butting in
Mark

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