linux-kernel - mmap issue.

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Date:	Fri, 17 Sep 2010 18:30:42 +0530
From:	naveen yadav <yad.naveen@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: mmap issue.

Hi All,

I am facing some issue while using mmap .

Issue 1.msync(ptr, PageSize, MS_ASYNC) if i pass MS_SYNC it fail with
bad option.
Issue 2. If i run the above program on target(ARM). the value is not changing

parent leaving critical section: -369098746
parent leaving critical section: -369098746
msync completed successfully
parent leaving critical section: -369098746
parent entered critical section -369098746



Thanks

But same program work well on Host machine.

parent leaving critical section: 12344
parent leaving critical section: 1000
msync completed successfully
parent leaving critical section: 1000
parent leaving critical section: 1000



#include <stdio.h>
#include <semaphore.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <errno.h>
#define SEM_NAME "mysem"
#define _SC_PAGE_SIZE 4096
int count = 100;


int main()
{
    int i, nloop = 1;
    sem_t *mutex;
    int fd, *ptr=NULL;
    int PageSize;
    fd = open ("/dev/mem", O_RDWR|O_SYNC);
    if (fd < 0) {
        printf("Failed while opening the memory descriptor\n");
        printf("Error is = %d\n", errno);
    }
    printf("\n============ PRIOR MAPPING ===========\n");
    char comm[50];
    sprintf(comm,"cat /proc/%d/maps",(int)getpid());
    system(comm);
    printf("============== PRIOR MAPPING =========\n\n");

/*    if ( (PageSize = sysconf(_SC_PAGE_SIZE)) < 0) {
       printf("sysconf() Error=");
       return -1;
   }
*/
       PageSize=4096;

    printf("\n============ PRIOR MAPPIN1 ===========\n");
    ptr = (int*)(mmap(NULL, PageSize, PROT_READ|PROT_WRITE,
MAP_SHARED, fd, 0));

    printf("\n============ PRIOR MAPPIN2 ===========\n");
    if (ptr == MAP_FAILED) {
        printf("MMAP failed\n");
        printf("value of errno is %d\n", errno);
        exit(0);
    }


  printf ("[%s] Mapped_buff_addr: [%8p]\n", __FUNCTION__, ptr);
    printf("\n============ NEW MAPPING ===========\n");
    //char comm[20];
    sprintf(comm,"cat /proc/%d/maps",(int)getpid());
    system(comm);
    printf("============== NEW MAPPING =========\n\n");
    printf("parent leaving critical section: %d\n", *ptr);
    *ptr = 1000;
    printf("parent leaving critical section: %d\n", *ptr);
    mutex = sem_open((SEM_NAME), O_CREAT | O_EXCL, S_IRWXU, 1);
    sem_unlink(SEM_NAME);
    setbuf(stdout, NULL); /* stdout is unbuffered */
    if (msync(ptr, PageSize, MS_ASYNC) < 0) { //naveen change to Async
        printf("Value of errno is %d\n", errno);
        printf("Value of page size is %d\n", PageSize);
        perror ("msync failed:");
        exit(0);
    }
    else {
        printf("msync completed successfully\n");
    }
    /* parent */
    for (i = 0; i < nloop; i++) {
        sem_wait(mutex);
       printf("parent leaving critical section: %d\n", *ptr);
        sleep(2);
        printf("parent leaving critical section: %d\n", *ptr);
        sem_post(mutex);
    }
    close(fd);
    return 0;
}
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