LinuxQuestions.org - mmap problem

hi

i created a programme who use a library.
the library talk to a driver.

the library need to write in shared memory between the application and kernel.

i try to use mmap.

in my application, i do:

Code:

static const int _MAXMSGSIZE = 256;

static const int _MAXMSGNB = 256;

int fd;



static char *mapdev (const char *, int, int);



int main (int argc, char **argv)

{

        unsigned int offset, size, i;

        char *addr, *addr1, *maddr;



        if (argc != 4)

        {

                fprintf (stderr, "Usage: mapcmp dev1 offset pages\n");

                exit (1);

        }

        size = _MAXMSGSIZE * _MAXMSGNB;

        

        maddr = malloc(size);

        

        offset = 0;

        

        addr = mapdev (argv[1], offset, size);

        

        addr1 = addr;



        

        for (i = 0; i < size; i++){

                *addr1 = "a";

                addr1++;

        }

        

        addr1 = addr;

        

        

        for (i = 0; i < size; i++){

                printf("%c",*addr1); 

                addr1++;

        }



        munmap(addr,size);

        close(fd);

        

        exit (0);

}



static char *mapdev (const char *dev, int offset, int size)

{

        char *addr;

        fd = open (dev, O_RDWR);



        printf("Va utiliser mmap1\n");

        

        if (fd < 0)

        {

                perror (dev);

                return (1);

        }

        printf("Va utiliser mmap2\n");

        

        addr = mmap (0, size, PROT_READ, MAP_PRIVATE, fd, offset);

        if (addr == MAP_FAILED)

        {

                perror (dev);

                return (1);

        }

        printf ("Mapped %s (%d @ %d) at 0x%p\n", dev, size, offset, addr);

        return (addr);

}

they are a problem when i do:

Code:

*addr1 = "a";

the machine freeze

any idea?