Re: Is shared memory now only for use by the kernel in 2.3.x????

From: Tigran Aivazian (
Date: Thu Apr 27 2000 - 15:28:43 EST

On Thu, 27 Apr 2000 wrote:
> Using 2.3.99pre6-6, I noticed that SHMMAX has been moved to linux/shm.h and
> that this file is only useable if you have __KERNEL__ defined, otherwise
> the headers it includes basically blow up due to symbols such as kdev_t not
> getting defined. Was this on purpose? If not, maybe we can fix this,
> because otherwise app builders using shared memory and trying to honor
> system boundaries are going to have some problems.

SHMMAX is a default value of kernel variable called shm_ctlmax which
happens to be a sysctl tunable and therefore is available by reading from
/proc/sys/kernel/shmmax. What's wrong with reading that file (apart from
being incompatible with other OSes)?

and, obviously, including <linux/shm.h> in a user app is a very bad idea,
but nobody stops you from doing so.


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