Re: shmget with SHM_HUGETLB flag: Operation not permitted

[Jochen Roemling]

William Lee Irwin III wrote:

> It's capable(CAP_IPC_LOCK) || in_group_p(0), not current->uid == 0.
> It will barf if you ask for more than either one of those limits. It
> will also barf if you ask for an amount not a multiple of the hugepage
> size. Please show the test program's code and strace the test program
> to determine what response it's getting.
>
>  
I attached the test pgm. It is nearly the same as shown
in Documentation/vm/hugetlbpage.txt

If you run it as root, it allocates 1 Hugepage, if run as user, it fails.

roesrv01:~ # ./a.out
shmid: 0x220004
shmaddr: 0x40167000
Starting the writes:
....
Starting the Check...Done.
roesrv01:~ # su - jochen
jochen@roesrv01:~> ./a.out
Failure:: Operation not permitted

I guess, a strace is not necessary.
The pgm has only the main function and only one position where it says 
"Failure"

What do I have to do to make this pgm run as an ordinary user with a 
stock kernel?

Curious...
Jochen
/* Example of using hugepage in user application using Sys V shared memory
 * system calls.  In this example, app is requesting memory of size 256MB that
 * is backed by huge pages.  Application uses the flag SHM_HUGETLB in shmget
 * system call to informt the kernel that it is requesting hugepages.  For
 * IA-64 architecture, Linux kernel reserves Region number 4 for hugepages.
 * That means the addresses starting with 0x800000....will need to be
 * specified.
 */
#include <sys/types.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <errno.h>

extern int errno;
#define SHM_HUGETLB 04000
#define LPAGE_SIZE      (4UL*1024UL*1024UL)
#define         dprintf(x)  printf(x)
#define ADDR (0x8000000000000000UL)
main()
{
        int shmid;
        int     i, j, k;
        volatile        char    *shmaddr;

	if ((shmid =shmget(IPC_PRIVATE, LPAGE_SIZE, SHM_HUGETLB|IPC_CREAT|SHM_R|SHM_W )) < 0) {
                perror("Failure:");
                exit(1);
        }
        printf("shmid: 0x%x\n", shmid);
        shmaddr = shmat(shmid, (void *)ADDR, SHM_RND) ;
        if (errno != 0) {
                perror("Shared Memory Attach Failure:");
                exit(2);
        }
        printf("shmaddr: %p\n", shmaddr);

        dprintf("Starting the writes:\n");
        for (i=0;i<LPAGE_SIZE;i++) {
                shmaddr[i] = (char) (i);
                if (!(i%(1024*1024))) dprintf(".");
        }
        dprintf("\n");
        dprintf("Starting the Check...");
        for (i=0; i<LPAGE_SIZE;i++)
                if (shmaddr[i] != (char)i)
                        printf("\nIndex %d mismatched.");
        dprintf("Done.\n");
        if (shmdt((const void *)shmaddr) != 0) {
                perror("Detached Failure:");
                exit (3);
        }
}