directio.c

/* -*- mode: c; c-basic-offset: 8; indent-tabs-mode: nil; -*-
 * vim:expandtab:shiftwidth=8:tabstop=8:
 */
#define  _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>

int main(int argc, char **argv)
{
        int fd;
        char *rbuf, *wbuf;
        int blocks, seek_blocks;
        long len;
        off64_t seek;
        struct stat64 st;
        int rc;

        if (argc < 4 || argc > 5) {
                printf("Usage: %s file seek nr_blocks [blocksize]\n", argv[0]);
                return 1;
        }

        seek_blocks = strtoul(argv[2], 0, 0);
        blocks = strtoul(argv[3], 0, 0);

        fd = open(argv[1], O_LARGEFILE | O_DIRECT | O_RDWR | O_CREAT, 0644);
        if (fd == -1) {
                printf("Cannot open %s:  %s\n", argv[1], strerror(errno));
                return 1;
        }

        if (argc == 5)
                st.st_blksize = strtoul(argv[4], 0, 0);
        else if (fstat64(fd, &st) < 0) {
                printf("Cannot stat %s:  %s\n", argv[1], strerror(errno));
                return 1;
        }

        printf("directio on %s for %dx%lu bytes \n", argv[1], blocks,
               st.st_blksize);

        seek = (off64_t)seek_blocks * (off64_t)st.st_blksize;
        if (lseek64(fd, seek, SEEK_SET) < 0) {
                printf("lseek64 failed: %s\n", strerror(errno));
                return 1;
        }

        len = blocks * st.st_blksize;
        wbuf = mmap(0, len, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, 0, 0);
        if (wbuf == MAP_FAILED) {
                printf("No memory %s\n", strerror(errno));
                return 1;
        }

        rbuf = mmap(0, len, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, 0, 0);
        if (rbuf == MAP_FAILED) {
                printf("No memory %s\n", strerror(errno));
                return 1;
        }

        memset(wbuf, 0xba, len);
        rc = write(fd, wbuf, len);
        if (rc != len) {
                printf("Write error %s (rc = %d)\n", strerror(errno), rc);
                return 1;
        }

        if (lseek64(fd, seek, SEEK_SET) < 0) {
                printf("Cannot seek %s\n", strerror(errno));
                return 1;
        }

        rc = read(fd, rbuf, len);
        if (rc != len) {
                printf("Read error: %s (rc = %d)\n", strerror(errno), rc);
                return 1;
        }

        if (memcmp(wbuf, rbuf, len)) {
                printf("Data mismatch\n");
                return 1;
        }

        printf("PASS\n");
        return 0;
}