/*
   Wei-keng Liao, EECS Department, Northwestern University
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#include <mpi.h>

#define NUM_INT 8

int main(int argc, char **argv) {
    int           i, err, rank, nprocs, blocklength, stride, *buffer;
    MPI_File      fh;
    MPI_Status    status;
    MPI_Datatype  fileType;
    MPI_Offset    disp;

    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &nprocs);

    if (argc != 2) {
        if (rank == 0) printf("Usage: %s filename\n",argv[0]);
        MPI_Finalize();
        return 1;
    }
    blocklength = 2 * NUM_INT;

    /* initialize the file contents to integers in increasing order */
    if (rank == 0) {
        char *fname = argv[1];
        if (0 == strncmp(argv[1], "ufs:", 4)) fname = argv[1]+4;
        int fd = open(fname, O_CREAT | O_RDWR, 0666);
        if (fd == -1) {
            printf("Error open() %s (error: %s)\n",fname,strerror(errno));
            MPI_Abort(MPI_COMM_WORLD, 1);
        }
        int total_int = nprocs*3*blocklength;
        buffer = (int*) malloc(total_int*sizeof(int));
        for (i=0; i<total_int; i++) buffer[i] = i;
        write(fd, buffer, total_int*sizeof(int));
        fsync(fd);
        close(fd);
        free(buffer);
    }
    MPI_Barrier(MPI_COMM_WORLD);

    /* open the file for read ------------------------------------------*/
    err = MPI_File_open(MPI_COMM_WORLD, argv[1], MPI_MODE_RDONLY, 
                        MPI_INFO_NULL, &fh);
    if (err != MPI_SUCCESS) {
        char err_string[MPI_MAX_ERROR_STRING+1];
        int  err_len;
        MPI_Error_string(err, err_string, &err_len);
        printf("Error: MPI_File_open() filename %s (%s)\n",argv[1],err_string);
        MPI_Finalize();
        exit(1);
    }

    /* define a non-contiguous file type -------------------------------*/
    /* illustration of this vector type:
     *   xxxxxxxxxx__________xxxxxxxxxx
     * when NUM_INT == 5 && blocklength == 10
     *
     * illustration of fileview:
     *   xxxxxxxxxx__________xxxxxxxxxxyyyyyyyyyy__________yyyyyyyyyy
     * when nprocs == 2, p0 reads xxxxx, p1 reads yyyyy (5 ints at a time)
     */
    disp   = 3 * blocklength * rank * sizeof(int);  /* in bytes */
    stride = 2 * blocklength * 2;
    MPI_Type_vector(2, blocklength, stride, MPI_INT, &fileType);
    MPI_Type_commit(&fileType);
    MPI_File_set_view(fh, disp, MPI_INT, fileType, "native", MPI_INFO_NULL);
    MPI_Type_free(&fileType);

    buffer = (int*) malloc(NUM_INT * sizeof(int));

    MPI_File_read_all(fh, buffer, NUM_INT, MPI_INT, &status);

    MPI_File_close(&fh);

    /* verify the read contents ------------------------------------------*/
    disp = 3 * blocklength * rank;
    for (i=0; i<NUM_INT; i++) {
        if (buffer[i] != i + disp) {
            printf("Read content error buffer[%d] = %d != %d\n",
                   i,buffer[i],i+disp);
            break;
        }
    }
    if (i == NUM_INT) printf("%2d: read verification succeed\n",rank);

    free(buffer);
    MPI_Finalize();

    return 0;
}