Newbie question about usage of mmap
 

Hi there,

I have a PCI device and I tried to write a short code to access it in user space with mmap.

first I "cat /proc/bus/pci/devices" and get the device's address: 0x00001800.

then I write the following code:

#include <sys/mman.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>

int main(void)
{
void *map;
int fd;
int src = 0;
ulong base;
ulong length;

base = 0x00001800;
length = 0xFF;

fd = open("/dev/mem", O_RDWR);
printf("%d\n",fd);
map = mmap(NULL, (size_t)length, (PROT_READ | PROT_WRITE), MAP_SHARED, fd,(off_t)base);
if (map == MAP_FAILED)
{
printf("map failed: %s\n",strerror(errno));
exit(1);
}

memcpy(map+0x85,&src, 1);

return 0;
}

I run the code and got the error says that "Invalid Argument", I guess that is because of some misuse of mmap, but where is the error?

TIA

justin

The offset (the last arg to mmap) must be multiple of the page size (4K on x86, 8K on 64-bit archs). Try just using an offset of zero and taking the 0x1800 into account when accessing the memory.