/* getdents test program.
 * Just read a single directory entry, using
 * a buffer exactly big enough.
 * This is the test program from the Linux getdents manpage,
 * with a few tweaks.
 */

#define _GNU_SOURCE
#include <dirent.h>     /* Defines DT_* constants */
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <string.h>

struct linux_dirent {
    long           d_ino;
    off_t          d_off;
    unsigned short d_reclen;
    char           d_name[];
};

#define BUF_SIZE 32

#define handle_error(msg) \
    do { perror(msg); exit(EXIT_FAILURE); } while (0)

#define CANARY 0xff

int main(int argc, char **argv)
{
    int fd, nread;
    char buf[BUF_SIZE * 2];
    struct linux_dirent *d;
    int bpos;
    char d_type;

    printf("linux_dirent struct size %ld bytes\n", sizeof(struct linux_dirent));
    printf("buffer space %d bytes\n", BUF_SIZE);
    memset(buf, CANARY, sizeof(buf));

    fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY);
    if (fd == -1)
        handle_error("open");

    for ( ; ; ) {
        nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
        if (nread == -1)
            handle_error("getdents");

        if (nread == 0)
            break;

        printf("--------------- nread=%d ---------------\n", nread);
        printf("inode#    file type  d_reclen  d_off   d_name\n");
        for (bpos = 0; bpos < nread;) {
            d = (struct linux_dirent *) (buf + bpos);
            printf("%8ld  ", d->d_ino);
            d_type = *(buf + bpos + d->d_reclen - 1);
            printf("%-10s ", (d_type == DT_REG) ?  "regular" :
                   (d_type == DT_DIR) ?  "directory" :
                   (d_type == DT_FIFO) ? "FIFO" :
                   (d_type == DT_SOCK) ? "socket" :
                   (d_type == DT_LNK) ?  "symlink" :
                   (d_type == DT_BLK) ?  "block dev" :
                   (d_type == DT_CHR) ?  "char dev" : "???");
            printf("%4d %10lld  %s\n", d->d_reclen,
                   (long long) d->d_off, d->d_name);
            bpos += d->d_reclen;
        }

        if ((unsigned char)buf[BUF_SIZE] != CANARY) {
            printf("Buffer overrun: syscall wrote past end of buffer\n");
            exit(1);
        }
    }

    exit(EXIT_SUCCESS);
}