Reading or mmaping from /dev/kmem

[embedded linux developer developer <em_li_de@xxxxxxxxxxx>]

Hi All,

 

I am using the Linux kernel 2.6.11 and I am having problems reading from /dev/kmem (though /dev/mem works fine). Both mmap and read on kmem is having problem. On my i386 machine I am trying to execute the following code and I am getting the errors

 

mmap failed: Input/output error

lseek returns c04a6000

read returns -1

read: Invalid argument

 

Would appreciate if someone could point out the problem.

 

Regards

Don

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

main()
{
	int fd;
	int addr;
	int x;

	fd = open("/dev/kmem", O_RDWR | O_SYNC );
	if(fd < 0)
	{
		perror("opening /dev/mem error:");
		exit(1);
	}

	addr = (int) mmap(NULL, 4096 , PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0xC04a6000);
	if(addr == -1)
	{
		perror("mmap failed:");
		//exit(1);
	}
	else 
		 printf("addreass read is %x\n",*(unsigned int *) (addr ));

	printf("lseek returns %x\n",lseek(fd, 0xC04a6000,SEEK_SET));
	printf("read returns %d\n",read(fd, (char *)&x, 4));
}