fs/Vfat.cpp

/*
 * Copyright (C) 2008 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 <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#include <linux/fs.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>

#include <linux/kdev_t.h>

#include <android-base/logging.h>
#include <android-base/stringprintf.h>
#include <selinux/selinux.h>

#include <logwrap/logwrap.h>

#include "Utils.h"
#include "Vfat.h"
#include "VoldUtil.h"

using android::base::StringPrintf;

namespace android {
namespace vold {
namespace vfat {

static const char* kMkfsPath = "/system/bin/newfs_msdos";
static const char* kFsckPath = "/system/bin/fsck_msdos";

bool IsSupported() {
    return access(kMkfsPath, X_OK) == 0 && access(kFsckPath, X_OK) == 0 &&
           IsFilesystemSupported("vfat");
}

status_t Check(const std::string& source) {
    int pass = 1;
    int rc = 0;
    do {
        std::vector<std::string> cmd;
        cmd.push_back(kFsckPath);
        cmd.push_back("-p");
        cmd.push_back("-f");
        cmd.push_back("-y");
        cmd.push_back(source);

        // Fat devices are currently always untrusted
        rc = ForkExecvpTimeout(cmd, kUntrustedFsckSleepTime, sFsckUntrustedContext);
        if (rc < 0) {
            LOG(ERROR) << "Filesystem check failed due to fork error";
            errno = EIO;
            return -1;
        }

        switch (rc) {
            case 0:
                LOG(INFO) << "Filesystem check completed OK";
                return 0;

            case 1:
                LOG(INFO) << "Failed to check filesystem";
                return -1;

            case 2:
                LOG(ERROR) << "Filesystem check failed (not a FAT filesystem)";
                errno = ENODATA;
                return -1;

            case 4:
                if (pass++ <= 3) {
                    LOG(WARNING) << "Filesystem modified - rechecking (pass " << pass << ")";
                    continue;
                }
                LOG(ERROR) << "Failing check after too many rechecks";
                errno = EIO;
                return -1;

            case 8:
                LOG(ERROR) << "Filesystem check failed (no filesystem)";
                errno = ENODATA;
                return -1;

            case ETIMEDOUT:
                LOG(ERROR) << "Filesystem check timed out";
                errno = ETIMEDOUT;
                return -1;

            default:
                LOG(ERROR) << "Filesystem check failed (unknown exit code " << rc << ")";
                errno = EIO;
                return -1;
        }
    } while (0);

    return 0;
}

int16_t currentUtcOffsetMinutes() {
    time_t now = time(NULL);

    struct tm nowTm;
    localtime_r(&now, &nowTm);

    int32_t utcOffsetSeconds = nowTm.tm_gmtoff;
    return (int16_t)(utcOffsetSeconds / 60);
}

status_t Mount(const std::string& source, const std::string& target, bool ro, bool remount,
               bool executable, int ownerUid, int ownerGid, int permMask, bool createLost) {
    int rc;
    unsigned long flags;

    const char* c_source = source.c_str();
    const char* c_target = target.c_str();

    flags = MS_NODEV | MS_NOSUID | MS_DIRSYNC | MS_NOATIME;

    flags |= (executable ? 0 : MS_NOEXEC);
    flags |= (ro ? MS_RDONLY : 0);
    flags |= (remount ? MS_REMOUNT : 0);

    auto mountData =
        android::base::StringPrintf("utf8,uid=%d,gid=%d,fmask=%o,dmask=%o,shortname=mixed",
                                    ownerUid, ownerGid, permMask, permMask);

    // b/315058275: Set this to false if you don't want to use a fixed offset
    // determined at mount time. When this is false, the vfat driver will fall
    // back to using sys_tz, which Android does not set by default, then assume
    // local time == UTC.
    if (true) {
        // Calculate the offset to use to adjust FAT timestamps to convert them
        // from "local time" into unix epoch time. This assumes the current UTC
        // offset of this device is the same as the device that wrote them. User
        // space code, e.g. ls -l, will then apply the UTC offset for the UTC
        // time to convert times from unix epoch time to local time for display.
        // Before Android U (b/246256335), Android platform code informed the
        // Linux kernel about the UTC offset under some circumstances, but not
        // for all, e.g. DST changes. The kernel vfat driver is one of the few
        // things in the kernel that tries to use kernel UTC offset information.
        // Setting time zone offset in the Linux kernel is discouraged and so
        // Android no longer informs the kernel. Instead, the offset for vfat
        // to use is now set at volume mount time. This means that if the time
        // zone offset changes while the device is mounted, or if files were
        // written in opposing daylight saving time, then incorrect file times
        // will be displayed until the volume is remounted. Even then, the vfat
        // driver has to assume a fixed offset to apply to all files, so files
        // written at different times of the year can have incorrect times
        // calculated, e.g. offset incorrectly by one hour.
        int16_t timeOffsetArg = currentUtcOffsetMinutes();
        mountData += android::base::StringPrintf(",time_offset=%d", timeOffsetArg);
    }

    rc = mount(c_source, c_target, "vfat", flags, mountData.c_str());

    if (rc && errno == EROFS) {
        LOG(ERROR) << source << " appears to be a read only filesystem - retrying mount RO";
        flags |= MS_RDONLY;
        rc = mount(c_source, c_target, "vfat", flags, mountData.c_str());
    }

    if (rc == 0 && createLost) {
        auto lost_path = android::base::StringPrintf("%s/LOST.DIR", target.c_str());
        if (access(lost_path.c_str(), F_OK)) {
            /*
             * Create a LOST.DIR in the root so we have somewhere to put
             * lost cluster chains (fsck_msdos doesn't currently do this)
             */
            if (mkdir(lost_path.c_str(), 0755)) {
                PLOG(ERROR) << "Unable to create LOST.DIR";
            }
        }
    }

    return rc;
}

status_t Format(const std::string& source, unsigned long numSectors) {
    std::vector<std::string> cmd;
    cmd.push_back(kMkfsPath);
    cmd.push_back("-O");
    cmd.push_back("android");
    cmd.push_back("-A");

    if (numSectors) {
        cmd.push_back("-s");
        cmd.push_back(StringPrintf("%lu", numSectors));
    }

    cmd.push_back(source);

    int rc = ForkExecvp(cmd);
    if (rc < 0) {
        LOG(ERROR) << "Filesystem format failed due to logwrap error";
        errno = EIO;
        return -1;
    }

    if (rc == 0) {
        LOG(INFO) << "Filesystem formatted OK";
        return 0;
    } else {
        LOG(ERROR) << "Format failed (unknown exit code " << rc << ")";
        errno = EIO;
        return -1;
    }
    return 0;
}

}  // namespace vfat
}  // namespace vold
}  // namespace android