请教rm.c的源代码

jeanne

我下了一个rm命令的源代码，看不明白，请高手详细讲解一下，不胜感激！#include <config.h>
#include <stdio.h>
#include <getopt.h>
#include <sys/types.h>
#include <assert.h>

#include "system.h"
#include "dirname.h"
#include "error.h"
#include "quote.h"
#include "remove.h"
#include "root-dev-ino.h"
#include "save-cwd.h"

/* The official name of this program (e.g., no `g' prefix).  */
#define PROGRAM_NAME "rm"

#define AUTHORS \
  "Paul Rubin", "David MacKenzie, Richard Stallman", "Jim Meyering"

/* Name this program was run with.  */
char *program_name;

/* For long options that have no equivalent short option, use a
   non-character as a pseudo short option, starting with CHAR_MAX + 1.  */
enum
{
  NO_PRESERVE_ROOT = CHAR_MAX + 1,
  PRESERVE_ROOT,
  PRESUME_INPUT_TTY_OPTION
};

static struct option const long_opts[] =
{
  {"directory", no_argument, NULL, 'd'},
  {"force", no_argument, NULL, 'f'},
  {"interactive", no_argument, NULL, 'i'},

  {"no-preserve-root", no_argument, 0, NO_PRESERVE_ROOT},
  {"preserve-root", no_argument, 0, PRESERVE_ROOT},

  /* This is solely for testing.  Do not document.  */
  /* It is relatively difficult to ensure that there is a tty on stdin.
     Since rm acts differently depending on that, without this option,
     it'd be harder to test the parts of rm that depend on that setting.  */
  {"presume-input-tty", no_argument, NULL, PRESUME_INPUT_TTY_OPTION},

  {"recursive", no_argument, NULL, 'r'},
  {"verbose", no_argument, NULL, 'v'},
  {GETOPT_HELP_OPTION_DECL},
  {GETOPT_VERSION_OPTION_DECL},
  {NULL, 0, NULL, 0}
};

void
usage (int status)
{
  if (status != EXIT_SUCCESS)
    fprintf (stderr, _("Try `%s --help' for more information.\n"),
             program_name);
  else
    {
      char *base = base_name (program_name);
      printf (_("Usage: %s [OPTION]... FILE...\n"), program_name);
      fputs (_("\
Remove (unlink) the FILE(s).\n\
\n\
  -d, --directory       unlink FILE, even if it is a non-empty directory\n\
                          (super-user only; this works only if your system\n\
                           supports `unlink' for nonempty directories)\n\
  -f, --force           ignore nonexistent files, never prompt\n\
  -i, --interactive     prompt before any removal\n\
"), stdout);
      fputs (_("\
      --no-preserve-root do not treat `/' specially (the default)\n\
      --preserve-root   fail to operate recursively on `/'\n\
  -r, -R, --recursive   remove the contents of directories recursively\n\
  -v, --verbose         explain what is being done\n\
"), stdout);
      fputs (HELP_OPTION_DESCRIPTION, stdout);
      fputs (VERSION_OPTION_DESCRIPTION, stdout);
      printf (_("\
\n\
To remove a file whose name starts with a `-', for example `-foo',\n\
use one of these commands:\n\
  %s -- -foo\n\
\n\
  %s ./-foo\n\
"),
              base, base);
      fputs (_("\
\n\
Note that if you use rm to remove a file, it is usually possible to recover\n\
the contents of that file.  If you want more assurance that the contents are\n\
truly unrecoverable, consider using shred.\n\
"), stdout);
      printf (_("\nReport bugs to <%s>.\n"), PACKAGE_BUGREPORT);
    }
  exit (status);
}

static void
rm_option_init (struct rm_options *x)
{
  x->unlink_dirs = 0;
  x->ignore_missing_files = 0;
  x->interactive = 0;
  x->recursive = 0;
  x->root_dev_ino = NULL;
  x->stdin_tty = isatty (STDIN_FILENO);
  x->verbose = 0;
}

int
main (int argc, char **argv)
{
  bool preserve_root = false;
  struct rm_options x;
  int fail = 0;
  int c;

  initialize_main (&argc, &argv);
  program_name = argv[0];
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);

  atexit (close_stdout);

  rm_option_init (&x);

  while ((c = getopt_long (argc, argv, "dfirvR", long_opts, NULL)) != -1)
    {
      switch (c)
        {
        case 0:                /* Long option.  */
          break;

        case 'd':
          x.unlink_dirs = 1;
          break;

        case 'f':
          x.interactive = 0;
          x.ignore_missing_files = 1;
          break;

        case 'i':
          x.interactive = 1;
          x.ignore_missing_files = 0;
          break;

        case 'r':
        case 'R':
          x.recursive = 1;
          break;

        case NO_PRESERVE_ROOT:
          preserve_root = false;
          break;

        case PRESERVE_ROOT:
          preserve_root = true;
          break;

        case PRESUME_INPUT_TTY_OPTION:
          x.stdin_tty = 1;
          break;

        case 'v':
          x.verbose = 1;
          break;

        case_GETOPT_HELP_CHAR;
        case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
        default:
          usage (EXIT_FAILURE);
        }
    }

  if (argc <= optind)
    {
      if (x.ignore_missing_files)
        exit (EXIT_SUCCESS);
      else
        {
          error (0, 0, _("too few arguments"));
          usage (EXIT_FAILURE);
        }
    }

  if (x.recursive && preserve_root)
    {
      static struct dev_ino dev_ino_buf;
      x.root_dev_ino = get_root_dev_ino (&dev_ino_buf);
      if (x.root_dev_ino == NULL)
        error (EXIT_FAILURE, errno, _("failed to get attributes of %s"),
               quote ("/"));
    }

  {
    size_t n_files = argc - optind;
    char const *const *file = (char const *const *) argv + optind;

    enum RM_status status = rm (n_files, file, &x);
    assert (VALID_STATUS (status));
    if (status == RM_ERROR)
      fail = 1;
  }

  exit (fail);
}
请大家不吝赐教！

Dragonfly

1) this is not kernel code
2) which line u can not understand? u can not ask people to comment every line for u.

jeanne

主要是以下这两段不太明白，而且它是通过什么系统调用来完成删除操作的呢？if (x.recursive && preserve_root)
{
static struct dev_ino dev_ino_buf;
x.root_dev_ino = get_root_dev_ino (&dev_ino_buf);
if (x.root_dev_ino == NULL)
error (EXIT_FAILURE, errno, _("failed to get attributes of %s"),
quote ("/"));
}

{
size_t n_files = argc - optind;
char const *const *file = (char const *const *) argv + optind;

enum RM_status status = rm (n_files, file, &x);
assert (VALID_STATUS (status));
if (status == RM_ERROR)
fail = 1;
}