libguestfs/daemon/9p.c

/* libguestfs - the guestfsd daemon
 * Copyright (C) 2011 Red Hat Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <config.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <limits.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>
#include <fcntl.h>

#include "daemon.h"
#include "actions.h"

#define BUS_PATH "/sys/bus/virtio/drivers/9pnet_virtio"

static char *read_whole_file (const char *filename);

/* https://bugzilla.redhat.com/show_bug.cgi?id=714981#c1 */
char **
do_list_9p (void)
{
  char **r = NULL;
  int size = 0, alloc = 0;

  DIR *dir;
  int err = 0;

  dir = opendir (BUS_PATH);
  if (!dir) {
    perror ("opendir: " BUS_PATH);
    if (errno != ENOENT)
      return NULL;

    /* If this directory doesn't exist, it probably means that
     * the virtio driver isn't loaded.  Don't return an error
     * in this case, but return an empty list.
     */
    if (add_string (&r, &size, &alloc, NULL) == -1)
      return NULL;

    return r;
  }

  while (1) {
    errno = 0;
    struct dirent *d = readdir (dir);
    if (d == NULL) break;

    if (STRPREFIX (d->d_name, "virtio")) {
      char mount_tag_path[256];
      snprintf (mount_tag_path, sizeof mount_tag_path,
                BUS_PATH "/%s/mount_tag", d->d_name);

      /* A bit unclear, but it looks like the virtio transport allows
       * the mount tag length to be unlimited (or up to 65536 bytes).
       * See: linux/include/linux/virtio_9p.h
       */
      char *mount_tag = read_whole_file (mount_tag_path);
      if (mount_tag == 0)
        continue;

      if (add_string (&r, &size, &alloc, mount_tag) == -1) {
        free (mount_tag);
        free_stringslen (r, size);
        closedir (dir);
        return NULL;
      }

      free (mount_tag);
    }
  }

  /* Check readdir didn't fail */
  if (errno != 0) {
    reply_with_perror ("readdir: /sys/block");
    free_stringslen (r, size);
    closedir (dir);
    return NULL;
  }

  /* Close the directory handle */
  if (closedir (dir) == -1) {
    reply_with_perror ("closedir: /sys/block");
    free_stringslen (r, size);
    return NULL;
  }

  /* Sort the tags.  Note that r might be NULL if there are no tags. */
  if (r != NULL)
    sort_strings (r, size);

  /* NULL terminate the list */
  if (add_string (&r, &size, &alloc, NULL) == -1)
    return NULL;

  return r;
}

/* Read whole file into dynamically allocated array.  If there is an
 * error, DON'T call reply_with_perror, just return NULL.  Returns a
 * \0-terminated string.
 */
static char *
read_whole_file (const char *filename)
{
  char *r = NULL;
  size_t alloc = 0, size = 0;
  int fd;

  fd = open (filename, O_RDONLY);
  if (fd == -1) {
    perror (filename);
    return NULL;
  }

  while (1) {
    alloc += 256;
    char *r2 = realloc (r, alloc);
    if (r2 == NULL) {
      perror ("realloc");
      free (r);
      return NULL;
    }
    r = r2;

    /* The '- 1' in the size calculation ensures there is space below
     * to add \0 to the end of the input.
     */
    ssize_t n = read (fd, r + size, alloc - size - 1);
    if (n == -1) {
      perror (filename);
      free (r);
      return NULL;
    }
    if (n == 0)
      break;
    size += n;
  }

  if (close (fd) == -1) {
    perror (filename);
    free (r);
    return NULL;
  }

  r[size] = '\0';

  return r;
}