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

int main(int argc, char **argv) {
    struct stat st;
    int fd = open(argv[1], O_RDWR|O_CREAT|O_TRUNC, 0600);
    if (fd == -1) {
        exit(1);
    }
    fstat(fd, &st);
    int rows = strtol(argv[2], NULL, 10), colls = strtol(argv[3], NULL, 10);
    int sz = rows * colls;
    ftruncate(fd, sz*sizeof(int));
    int *buf = mmap(NULL, sz*sizeof(int), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
    int i=0, j, k = 0, p=1;
    while (i !=  sz) {
        ++k;
        for (j=k-1;j!= colls-k+1; ++j) {
            buf[colls*(k-1)+j]=p++;
            ++i;
        }
        for (j=k;j!= rows-k+1; ++j) {
            buf[colls*(j)+colls-k]=p++;
            ++i;
        }
        for (j=colls-k-1;j>=k-1; --j) {
            buf[colls*(rows-k)+j]=p++;
            ++i;
        }
        for (j=rows-k-1;j>=k; --j) {
            buf[colls*(j)+k-1]=p++;
            ++i;
        }
    }
    munmap(buf, sz * sizeof(int));
}