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

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Date:	Fri, 31 Jan 2014 12:05:00 -0500
From:	"Austin S. Hemmelgarn" <ahferroin7@...il.com>
To:	Network Nut <sillystack@...il.com>,
	'Clemens Ladisch' <clemens@...isch.de>
CC:	linux-kernel@...r.kernel.org
Subject: Re: WaitForMultipleObjects/etc. In Kernel



On 01/30/2014 06:49 PM, Network Nut wrote:
>> -----Original Message-----
>> From: Clemens Ladisch [mailto:clemens@...isch.de]
>> Sent: Wednesday, January 29, 2014 2:31 AM
>> To: Network Nut
>> Cc: linux-kernel@...r.kernel.org
>> Subject: RE: WaitForMultipleObjects/etc. In Kernel
>>
>> Network Nut wrote:
>>> I was looking at POSIX because it allows naming of the primitives.
>>
>> Linux uses two orthogonal mechanisms for synchronization primitives and for
>> naming/sharing.
>>
>>> I need to epoll_wait on inter-process {mutex, event, semaphore}.
>>
>> Use eventfd.
>>
>>> I need to reference inter-process {mutex, event, semaphore}, each
>>> identified by string, if feasible.
>>
>> Send the fd through a Unix domain socket.
> 
> Hi Again,
> 
> 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.
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