platform_bootable_recovery/fuse_sdcard_provider.cpp

/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "fuse_sdcard_provider.h"

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <unistd.h>

#include <functional>

#include <android-base/file.h>

#include "fuse_sideload.h"

struct file_data {
  int fd;  // the underlying sdcard file

  uint64_t file_size;
  uint32_t block_size;
};

static int read_block_file(const file_data& fd, uint32_t block, uint8_t* buffer,
                           uint32_t fetch_size) {
  off64_t offset = static_cast<off64_t>(block) * fd.block_size;
  if (TEMP_FAILURE_RETRY(lseek64(fd.fd, offset, SEEK_SET)) == -1) {
    fprintf(stderr, "seek on sdcard failed: %s\n", strerror(errno));
    return -EIO;
  }

  if (!android::base::ReadFully(fd.fd, buffer, fetch_size)) {
    fprintf(stderr, "read on sdcard failed: %s\n", strerror(errno));
    return -EIO;
  }

  return 0;
}

bool start_sdcard_fuse(const char* path) {
  struct stat sb;
  if (stat(path, &sb) == -1) {
    fprintf(stderr, "failed to stat %s: %s\n", path, strerror(errno));
    return false;
  }

  file_data fd;
  fd.fd = open(path, O_RDONLY);
  if (fd.fd == -1) {
    fprintf(stderr, "failed to open %s: %s\n", path, strerror(errno));
    return false;
  }
  fd.file_size = sb.st_size;
  fd.block_size = 65536;

  provider_vtab vtab;
  vtab.read_block = std::bind(&read_block_file, fd, std::placeholders::_1, std::placeholders::_2,
                              std::placeholders::_3);
  vtab.close = [&fd]() { close(fd.fd); };

  // The installation process expects to find the sdcard unmounted. Unmount it with MNT_DETACH so
  // that our open file continues to work but new references see it as unmounted.
  umount2("/sdcard", MNT_DETACH);

  return run_fuse_sideload(vtab, fd.file_size, fd.block_size) == 0;
}