#include <stdio.h>
#include <stdint.h>
#include <unistd.h>
#include <sys/types.h>
#include <errno.h>

#define RW_MAX_SIZE    0x7ffff000


ssize_t read_from_buffer(char *fname, int fd, char *buffer, uint64_t size, uint64_t base) {
    ssize_t rc;
    char *buf = buffer;
    off_t offset = base;
    size_t count = 0;
    int loop = 0;

    while (count < size) {
        uint64_t bytes = size - count;

        if (bytes > RW_MAX_SIZE) {
            bytes = RW_MAX_SIZE;
        }
        if (offset) {
            rc = lseek(fd, offset, SEEK_SET);
            if (rc != offset) {
                fprintf(stderr, "%s, seek off 0x%lx != 0x%lx\n", fname, rc, offset);
                perror("seek file");
                return -EIO;
            }
        }
        /* Read data from file into buffer */
        rc = read(fd, buf, bytes);
        if (rc < 0) {
            fprintf(stderr, "%s, read failed\n", fname);
            perror("read file");
            return -EIO;
        }
        count += rc;
        if (rc != bytes) {
            fprintf(stderr, "%s, read failed, rc=%ld, bytes=%ld\n", fname, rc, bytes);
            break;
        }
        buf += bytes;
        offset += bytes;
        loop++;
    }
    if (count != size && loop) {
        fprintf(stderr, "%s, read failed, count=%ld, size=%ld\n", fname, count, size);
        return -EIO;
    }
    return count;
}

ssize_t write_to_buffer(char *fname, int fd, char *buffer, uint64_t size, uint64_t base) {
    ssize_t rc;
    char *buf = buffer;
    off_t offset = base;
    size_t count = 0;
    int loop = 0;

    while (count < size) {
        uint64_t bytes = size - count;

        if (bytes > RW_MAX_SIZE) {
            bytes = RW_MAX_SIZE;
        }
        if (offset) {
            rc = lseek(fd, offset, SEEK_SET);
            if (rc != offset) {
                fprintf(stderr, "%s, seek off 0x%lx != 0x%lx\n", fname, rc, offset);
                perror("seek file");
                return -EIO;
            }
        }
        /* Write data from buffer into file */
        rc = write(fd, buf, bytes);
        if (rc < 0) {
            fprintf(stderr, "%s,write 0x%lx @ 0x%lx @ 0x%lx failed %ld.\n", fname, bytes, offset, rc);
            perror("write file");
            return -EIO;
        }
        count += rc;
        printf("count = %ld, bytes = %ld\n", count, size);
        if (rc != bytes) {
            fprintf(stderr, "%s, write underflow 0x%lx/0x%lx @ 0x%lx.\n", fname, rc, bytes, offset);
            break;
        }
        buf += bytes;
        offset += bytes;
        loop++;
    }
    if (count != size && loop) {
        fprintf(stderr, "%s, write underflow, 0x%lx/0x%lx.\n", fname, count, size);
        return -EIO;
    }
    return count;
}