Message-ID: <52EBD7BC.5020704@gmail.com>
Date: Fri, 31 Jan 2014 12:05:00 -0500
From: "Austin S. Hemmelgarn" <ahferroin7@gmail.com>
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To: Network Nut <sillystack@gmail.com>,
        "'Clemens Ladisch'" <clemens@ladisch.de>
CC: linux-kernel@vger.kernel.org
Subject: Re: WaitForMultipleObjects/etc. In Kernel
References: <00d901cf1a19$0ea62db0$2bf28910$@gmail.com> <52E554EC.3090900@ladisch.de> <012d01cf1ae3$6543e340$2fcba9c0$@gmail.com> <52E6219A.3020405@ladisch.de> <00d001cf1b99$026407d0$072c1770$@gmail.com> <52E77282.4030303@ladisch.de> <009701cf1c6c$fbfaff50$f3f0fdf0$@gmail.com> <95b6e508-1358-4f01-9687-344e25bd4b2b@email.android.com> <00f201cf1e15$f134ce70$d39e6b50$@gmail.com>
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On 01/30/2014 06:49 PM, Network Nut wrote:
>> -----Original Message-----
>> From: Clemens Ladisch [mailto:clemens@ladisch.de]
>> Sent: Wednesday, January 29, 2014 2:31 AM
>> To: Network Nut
>> Cc: linux-kernel@vger.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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