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From: "Dirk Bull" <dirkbull102@hotmail.com>
To: doug@mcnaught.org
Cc: linux-kernel@vger.kernel.org
Subject: Re: shmat problem
Date: Mon, 06 Jan 2003 14:53:41 +0000
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Doug, thanks for the reply. I've set SHM_RND in the call and used
"__attribute__ ((aligned(4096)))" during the the declaration of variable 
global01_
(as shown below) such that it is aligned on a page boundary. I'm porting 
code that was
written for a Unix system to Linux and the example shown below is how the 
code is
implemented on Unix.

The example included executed correctly on :
mandrake - ? (Can't remember, but it was an old version)

but fails to work on:
redhat - 2.2.14-5.0
debian - 2.2.9
mandrake - 2.4.19-16mdk



We are currently working on mandrake - kernel 2.4.19-16mdk.


Dirk

-------------------------------------------------------------------------------
Example program:
-------------------------------------------------------------------------------

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <errno.h>

#define SHM_MODE (SHM_R | SHM_W)

union {
	long IN[2048];
} global01_ __attribute__ ((aligned(4096)));

int main(void) {
	int shmid;
	char *shmptr;


	if ( (shmid = shmget(IPC_PRIVATE, sizeof(global01_), SHM_MODE)) < 0){
		printf("shmget error: %d %s\n",errno, strerror(errno));
		exit(0);
	}

	if ( (shmptr = shmat(shmid, &global01_, SHM_RND)) == (void *) -1)
		printf("shmat error: %d %s\n",errno, strerror(errno));
	else
		printf("shared memory attached from %x to %x\n",
				shmptr, shmptr+sizeof(global01_));

	if (shmctl(shmid, IPC_RMID, 0) < 0)
		printf("shmctl error: %d %s\n",errno, strerror(errno));

	exit(0);
}









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