[Buildroot] device_table & /dev/shm

Khem Raj raj.khem at gmail.com
Sat Jun 25 23:40:45 UTC 2011

On 06/25/2011 11:29 AM, Charles Krinke wrote:
> I have two issues I dont understand and am hoping for a few clues to
> help me navigate through the "Swamp of Confusion" to the "Ridge of
> Enlightment".
> 1. I can see the generic device_table.txt and it includes a /dev/shm
> node. I can also see the /dev structure in output/target and it
> matches the generic device_table.txt. But, ... when I build the jffs2
> and load it on my MPC8323 target, what I see in /dev does not include
> /dev/shm. In fact it is significantly different. So, my first question
> is:
> "What besides generic/device_table.txt can determine the contents of
> /dev on an MPC8323 target?"

I would check shm support in kernel is enabled or not
and /etc/mtab has /dev/shm entry or not.

> 2. I can see that named semaphores are not working. That is,
> sem_open() called from an application program fails with ENOSYS. In
> researching this, I can see that this depends on part on /dev/shm and
> linking with -lrt. It also appears that the default /etc/fstab does
> not use /dev/shm. My second question is:

I think its because of above problem.

> "What are the items that can go awry in an MPC8323 system that may
> cause named semaphores using the sem_open() call to fail?"

Depends if you are using applications that rely on shm_*

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