/* MZM - memory mapped disk baked toy allocator.
 *
 * Copyright 2010 Salvatore Sanfilippo, BSD licensed. */

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

#define MEMORYZM_INITIAL_SIZE (4096*1024*8)
#define MZM_BASE_ADDR 0x10000000

static unsigned long cursize, curoff;

/* Returns NULL if there was no pre-existing state.
 * Otherwise the address of the first allocation is returned. */
void *zmzInit(void) {
    int fd = open("memory.zm",O_CREAT|O_RDWR,0644);
    struct stat buf;
    /* The first allocation is at base address plus a first long value
     * used to store the current offset, plus a second long value that
     * is the header of every allocation. */
    void *retval = (void*)(MZM_BASE_ADDR+(sizeof(long)*2));

    if (fd == -1) {
        perror("opening memory.zm");
        exit(1);
    }
    if (fstat(fd, &buf) == -1) {
        perror("fstat(2) against memory.zm");
        exit(1);
    }

    /* Mmap the file starting from our base address */
    cursize = buf.st_size;

    /* If there was not pre-existing state initalize it, otherwise
     * just read the old offset. */
    printf("cursize: %lu\n",cursize);
    if (cursize == 0) {
        long *x;

        retval = NULL;
        if (ftruncate(fd,MEMORYZM_INITIAL_SIZE) == -1) {
            perror("ftruncate(2) against memory.zm");
            exit(1);
        }
        cursize = MEMORYZM_INITIAL_SIZE;
        printf("Mmap-ping...\n");
        if (mmap((void*)MZM_BASE_ADDR,cursize,PROT_READ|PROT_WRITE,
                 MAP_FILE|MAP_FIXED|MAP_SHARED,fd,0) == MAP_FAILED) {
            perror("mmap(2) in MZM");
            exit(1);
        }
        printf("OK\n"); fflush(stdout);

        curoff = (unsigned long) (MZM_BASE_ADDR+sizeof(long));
        x = (long*) MZM_BASE_ADDR;
        *x = curoff;
    } else {
        long *x;

        if (mmap((void*)MZM_BASE_ADDR,cursize,PROT_READ|PROT_WRITE,
                 MAP_FILE|MAP_FIXED|MAP_SHARED,fd,0) == MAP_FAILED) {
            perror("mmap(2) in MZM");
            exit(1);
        }

        x = (long*) MZM_BASE_ADDR;
        curoff = *x;
    }
    return retval;
}

void *zmalloc(size_t size) {
    unsigned long *x = (unsigned long*) curoff;
    unsigned long *curoffp = (unsigned long*) MZM_BASE_ADDR;

    curoff += sizeof(unsigned long)+size;
    *curoffp = curoff;
    *x = (unsigned long) size;
    x++;
    return x;
}

#include <string.h>
int main(void) {
    void *firstalloc = zmzInit();
    char *p;

    if (firstalloc == NULL) {
        printf("First allocation\n");
        p = zmalloc(7);
        memcpy(p,"foobar\0",7);
    } else {
        printf("Second run\n");
        p = firstalloc;
    }
    printf("String is: %s\n", p);
    return 0;
}