使用getdents（）转到代码以列出Linux目录中的文件

Question

As an exercise, I wanted to translate some C code that used many syscalls into Golang. I found this nice code example on Unix & Linux StackExchange:

/*
 * List directories using getdents() because ls, find and Python libraries
 * use readdir() which is slower (but uses getdents() underneath.
 *
 * Compile with 
 * ]$ gcc  getdents.c -o getdents
 */
#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>

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

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

#define BUF_SIZE 1024*1024*5

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

   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;

       for (bpos = 0; bpos < nread;) {
           d = (struct linux_dirent *) (buf + bpos);
           d_type = *(buf + bpos + d->d_reclen - 1);
           if( d->d_ino != 0 && d_type == DT_REG ) {
              printf("%s
", (char *)d->d_name );
           }
           bpos += d->d_reclen;
       }
   }

   exit(EXIT_SUCCESS);
}

I have only been able to code this using ioutil.ReadDir which defeats the purpose. Does anyone have an idea on how to translate this?

Answer 1

I would avoid using this code. As written, it's wrong: on 32-bit systems and maybe even some 64-bit ones, SYS_getdents is the legacy syscall that doesn't provide d_type and lacks support for 64-bit inode numbers, which means you get gratuitous errors on modern filesystems. Even if you fix it, it's no better than inlining readdir, which does basically exactly the same thing internally.