linux-kernel - RE: WaitForMultipleObjects/etc. In Kernel

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Message-ID: <007d01cf1ed4$b0e659a0$12b30ce0$@gmail.com>
Date:	Fri, 31 Jan 2014 16:35:05 -0600
From:	"Network Nut" <sillystack@...il.com>
To:	"'Austin S. Hemmelgarn'" <ahferroin7@...il.com>,
	"'Clemens Ladisch'" <clemens@...isch.de>
Cc:	<linux-kernel@...r.kernel.org>
Subject: RE: WaitForMultipleObjects/etc. In Kernel

> -----Original Message-----
> From: Austin S. Hemmelgarn [mailto:ahferroin7@...il.com]
> Sent: Friday, January 31, 2014 11:05 AM
> To: Network Nut; 'Clemens Ladisch'
> Cc: linux-kernel@...r.kernel.org
> Subject: Re: WaitForMultipleObjects/etc. In Kernel

> >> Network Nut wrote:
> > I was thinking that, rather than as for specifics, I should present my general
> problem, and ask how long-time Linux experts would solve it.
> >
> > I have a master process M, that executes continually, from the birth to
> death of user-session.
> >
> > I have many (distinct) processes that will be launched, and these
> processes, P1, P2, ...Pn, expect to see that M is executing. These processes:
> >
> > 1. expect to have access to a shared-memory section that already exists
> because M created it
> > 2. expect to use a semaphore that already exists because M created it
> > 3. expect to use a mutex that exists because M created it
> >
> > P1, P2, ...Pn all know the path of image on disk of M. They are also
> permitted to maintain a fixed string that can be used to "get at" the mutex
> and semaphore.
> >
> > How would P1, P2, ...Pn get at the semaphore that M created?
> >
> > Please note that M cannot have any prior knowledge at all of P1, P2, ...Pn.
> P1...etc. must initiate  communication with M.
> >
> > [I don't want to misuse/abuse linux-kernel with my personal questions, so
> if there is a more appropriate group, please let me know.]
> >
> > Regards,
> >
> > -Net
> Assuming that you're porting to mainline distributions (and not embedded
> devices), named SHM segments are accessible (providing the accessing
> process has correct permissions) under /dev/shm.  You just need to make
> sure that you create the segment with the right permissions for the
> other processes to access it.

Thanks, Austin.

I already know how to do named shared memory between two processes. I only included that to describe my overall problem.

The problem that I am having is how I can make three totally-independent processes interact:

1. M is a master process that creates a semaphore.
2. P1 is a process that operates against the semaphore.
3. P2 is a process that operates against the semaphore.
4. It is not permissible that M be responsible for launching P1 or P2.
5.  The semaphore, one way or another, must allow itself to be specified as one of the synchronization primitives in epoll_wait()

How do I do this?

-Nut

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