mmap problem

os2 · 06-20-2004, 07:58 PM

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?

Dark_Helmet · 06-20-2004, 08:12 PM

I don't know if this will solve your problem, but you're trying to assign a string to a character.

*addr1 is the location of a single character in memory.
"a" is a string (not a single character; use single quotes to specify a character)

Try:

Code:

*addr1 = 'a';

infamous41md · 06-20-2004, 09:14 PM

when u say 'the machine freezes', do u mean the entire machine hangs and u have to reboot?? if so, can u plz tell me what device it is you are trying to open?

os2 · 06-21-2004, 03:39 PM

no not need to reboot... i can kill the application

i got the same problem, Dark_Helmet with your solution

infamous41md · 06-21-2004, 05:24 PM

you are only specifying PROT_READ, and u r trying to write to the memory.