automount.c

Android 一些工具

/*
 * 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.
 */

/*
** mountd automount support
*/

#include "mountd.h"

#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <ctype.h>
#include <pwd.h>
#include <stdlib.h>
#include <poll.h>

#include <sys/mount.h>
#include <sys/stat.h>
#include <linux/loop.h>
#include <sys/inotify.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <linux/netlink.h>

#define DEVPATH    "/dev/block/"
#define DEVPATHLENGTH 11    // strlen(DEVPATH)

// FIXME - only one loop mount is supported at a time
#define LOOP_DEVICE "/dev/block/loop0"

// timeout value for poll() when retries are pending
#define POLL_TIMEOUT    1000

#define MAX_MOUNT_RETRIES   3
#define MAX_UNMOUNT_RETRIES   5

typedef enum {
    // device is unmounted
    kUnmounted,
    
    // attempting to mount device
    kMounting,
    
    // device is unmounted
    kMounted,
    
    // attempting to unmount device
    // so the media can be removed
    kUnmountingForEject,
    
    // attempting to mount device
    // so it can be shared via USB mass storage
    kUnmountingForUms,
} MountState;

typedef struct MountPoint {
    // block device to mount
    const char* device;
    
    // mount point for device
    const char* mountPoint;
    
    // true if device can be shared via
    // USB mass storage
    boolean enableUms;
    
    // true if the device is being shared via USB mass storage
    boolean umsActive;
    
    // logical unit number (for UMS)
    int lun;
    
    // current state of the mount point
    MountState state;
    
    // number of mount or unmount retries so far, 
    // when attempting to mount or unmount the device
    int retryCount; 
 
    // next in sMountPointList linked list
    struct MountPoint* next;   
} MountPoint;

// list of our mount points (does not change after initialization)
static MountPoint* sMountPointList = NULL;
static int sNextLun = 0;
boolean gMassStorageEnabled = false;
boolean gMassStorageConnected = false;

static pthread_t sAutoMountThread = 0;

// number of mount points that have timeouts pending
static int sRetriesPending = 0;

// for synchronization between sAutoMountThread and the server thread
static pthread_mutex_t sMutex = PTHREAD_MUTEX_INITIALIZER;

// requests the USB mass_storage driver to begin or end sharing a block device
// via USB mass storage.
static void SetBackingStore(MountPoint* mp, boolean enable) 
{
    char path[PATH_MAX];
    int fd;

    LOG_MOUNT("SetBackingStore enable: %s\n", (enable ? "true" : "false"));
    snprintf(path, sizeof(path), "/sys/devices/platform/usb_mass_storage/lun%d/file", mp->lun);
    fd = open(path, O_WRONLY);
    if (fd < 0)
    {
        LOG_ERROR("could not open %s\n", path);
    }
    else
    {
        if (enable)
        {
            write(fd, mp->device, strlen(mp->device));
            mp->umsActive = true;
        }
        else
        {
            char ch = 0;
            write(fd, &ch, 1);
            mp->umsActive = false;
        }
        close(fd);
    }
}

static boolean ReadMassStorageState()
{
    FILE* file = fopen("/sys/class/switch/usb_mass_storage/state", "r");
    if (file)
    {
        char    buffer[20];
        fgets(buffer, sizeof(buffer), file);
        fclose(file);
        return (strncmp(buffer, "online", strlen("online")) == 0);
    }
    else
    {
        LOG_ERROR("could not read initial mass storage state\n");
        return false;
    }
}

static boolean IsLoopMounted(const char* path)
{
    FILE* f;
    int count;
    char device[256];
    char mount_path[256];
    char rest[256];
    int result = 0;
    int path_length = strlen(path);
       
    f = fopen("/proc/mounts", "r");
    if (!f) {
        LOG_ERROR("could not open /proc/mounts\n");
        return -1;
    }

    do {
        count = fscanf(f, "%255s %255s %255s\n", device, mount_path, rest);
        if (count == 3) {
            if (strcmp(LOOP_DEVICE, device) == 0 && strcmp(path, mount_path) == 0)
            {
                result = 1;
                break;
            }
        }
    } while (count == 3);

    fclose(f);
    LOG_MOUNT("IsLoopMounted: %s returning %d\n", path, result);
    return result;
}

static int DoMountDevice(const char* device, const char* mountPoint)
{
    LOG_MOUNT("mounting %s at %s\n", device, mountPoint);

#if CREATE_MOUNT_POINTS
    // make sure mount point exists
    mkdir(mountPoint, 0000);
#endif

    int flags = 0;
    
    if (device && strncmp(device, "/dev/", 5))
    {
        // mount with the loop driver if device does not start with "/dev/"
        int file_fd, device_fd;
        
        // FIXME - only one loop mount supported at a time
        file_fd = open(device, O_RDWR);
        if (file_fd < -1) {
            LOG_ERROR("open backing file %s failed\n", device);
            return 1;
        }
        device_fd = open(LOOP_DEVICE, O_RDWR);
        if (device_fd < -1) {
            LOG_ERROR("open %s failed", LOOP_DEVICE);
            close(file_fd);
            return 1;
        }
        if (ioctl(device_fd, LOOP_SET_FD, file_fd) < 0)
        {
            LOG_ERROR("ioctl LOOP_SET_FD failed\n");
            close(file_fd);
            close(device_fd);
            return 1;
        }

        close(file_fd);
        close(device_fd);
        device = "/dev/block/loop0";
    }

    int result = access(device, R_OK);
    if (result != 0)
        return result;

    // Extra safety measures:
    flags |= MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_DIRSYNC;
    // Also, set fmask = 711 so that files cannot be marked executable,
    // and cannot by opened by uid 1000 (system). Similar, dmask = 700
    // so that directories cannot be accessed by uid 1000.
    result = mount(device, mountPoint, "vfat", flags, 
                       "utf8,uid=1000,gid=1000,fmask=711,dmask=700");
    if (result && errno == EROFS) {
        LOG_ERROR("mount failed EROFS, try again read-only\n");
        flags |= MS_RDONLY;
        result = mount(device, mountPoint, "vfat", flags,
                       "utf8,uid=1000,gid=1000,fmask=711,dmask=700");
    }
    LOG_MOUNT("mount returned %d errno: %d\n", result, errno);

    if (result == 0) {
        NotifyMediaState(mountPoint, MEDIA_MOUNTED, (flags & MS_RDONLY) != 0);
    } else if (errno == EBUSY) {
    // ignore EBUSY, since it usually means the device is already mounted
        result = 0;
    } else {
#if CREATE_MOUNT_POINTS
        rmdir(mountPoint);
#endif
        LOG_MOUNT("mount failed, errno: %d\n", errno);
    }

    return result;
}

static int DoUnmountDevice(const char* mountPoint)
{
    boolean loop = IsLoopMounted(mountPoint);
    int result = umount(mountPoint);
    LOG_MOUNT("umount returned %d errno: %d\n", result, errno);

    if (result == 0)
    {
        if (loop)
        {
            // free the loop device
            int loop_fd = open(LOOP_DEVICE, O_RDONLY);
            if (loop_fd < -1) {
                LOG_ERROR("open loop device failed\n");
            }
            if (ioctl(loop_fd, LOOP_CLR_FD, 0) < 0) {
                LOG_ERROR("ioctl LOOP_CLR_FD failed\n");
            }

            close(loop_fd);
        }

#if CREATE_MOUNT_POINTS
        rmdir(mountPoint);
#endif
        NotifyMediaState(mountPoint, MEDIA_UNMOUNTED, false);
    }

    // ignore EINVAL and ENOENT, since it usually means the device is already unmounted
    if (result && (errno == EINVAL || errno == ENOENT))
        result = 0;

    return result;
}

static int MountPartition(const char* device, const char* mountPoint)
{
    char    buf[100];
    int i;
    
    // attempt to mount subpartitions of the device
    for (i = 1; i < 10; i++)
    {
        snprintf(buf, sizeof(buf), "%sp%d", device, i);
        if (DoMountDevice(buf, mountPoint) == 0)
            return 0;
    }

    return -1;
}

/*****************************************************
 * 
 * AUTO-MOUNTER STATE ENGINE IMPLEMENTATION
 * 
 *****************************************************/

static void SetState(MountPoint* mp, MountState state)
{
    mp->state = state;
}

// Enter a state that requires retries and timeouts.
static void SetRetries(MountPoint* mp, MountState state)
{
    SetState(mp, state);
    mp->retryCount = 0;

    sRetriesPending++;
    // wake up the automounter thread if we are being called 
    // from somewhere else with no retries pending
    if (sRetriesPending == 1 && sAutoMountThread != 0 && 
            pthread_self() != sAutoMountThread)
        pthread_kill(sAutoMountThread, SIGUSR1);
}

// Exit a state that requires retries and timeouts.
static void ClearRetries(MountPoint* mp, MountState state)
{
    SetState(mp, state);
    sRetriesPending--;
}

// attempt to mount the specified mount point.
// set up retry/timeout if it does not succeed at first.
static void RequestMount(MountPoint* mp)
{
    LOG_MOUNT("RequestMount %s\n", mp->mountPoint);

    if (mp->state != kMounted && mp->state != kMounting &&
            access(mp->device, R_OK) == 0) {
        // try raw device first
        if (DoMountDevice(mp->device, mp->mountPoint) == 0 ||
            MountPartition(mp->device, mp->mountPoint) == 0)
        {
            SetState(mp, kMounted);
        }
        else 
        {
            SetState(mp, kMounting);
            mp->retryCount = 0;
            SetRetries(mp, kMounting);
        }
    }
}

// Force the kernel to drop all caches.
static void DropSystemCaches(void)
{
    int fd;

    LOG_MOUNT("Dropping system caches\n");
    fd = open("/proc/sys/vm/drop_caches", O_WRONLY);

    if (fd > 0) {
        char ch = 3;
        int rc;

        rc = write(fd, &ch, 1);
        if (rc <= 0)
            LOG_MOUNT("Error dropping caches (%d)\n", rc);
        close(fd);
    }
}

// attempt to unmount the specified mount point.
// set up retry/timeout if it does not succeed at first.
static void RequestUnmount(MountPoint* mp, MountState retryState)
{
    int result;

    LOG_MOUNT("RequestUnmount %s retryState: %d\n", mp->mountPoint, retryState);
    
    if (mp->state == kMounted)
    {
        SendUnmountRequest(mp->mountPoint);

        // do this in case the user pulls the SD card before we can successfully unmount
        sync();
        DropSystemCaches();

        if (DoUnmountDevice(mp->mountPoint) == 0) 
        {
            SetState(mp, kUnmounted);
            if (retryState == kUnmountingForUms) 
            {
                SetBackingStore(mp, true);
                NotifyMediaState(mp->mountPoint, MEDIA_SHARED, false);
            }
        }
        else 
        {
            LOG_MOUNT("unmount failed, set retry\n");
            SetRetries(mp, retryState);
        }
    } 
    else if (mp->state == kMounting)
    {
        SetState(mp, kUnmounted);
    }
}

// returns true if the mount point should be shared via USB mass storage
static boolean MassStorageEnabledForMountPoint(const MountPoint* mp)
{
    return (gMassStorageEnabled && gMassStorageConnected && mp->enableUms);
}

// handles changes in gMassStorageEnabled and gMassStorageConnected
static void MassStorageStateChanged()
{
    MountPoint* mp = sMountPointList;

    boolean enable = (gMassStorageEnabled && gMassStorageConnected);
    LOG_MOUNT("MassStorageStateChanged enable: %s\n", (enable ? "true" : "false"));
    
    while (mp)
    {
        if (mp->enableUms)
        {
            if (enable)
            {
                if (mp->state == kMounting)
                    SetState(mp, kUnmounted);
                if (mp->state == kUnmounted) 
                {
                    SetBackingStore(mp, true);
                    NotifyMediaState(mp->mountPoint, MEDIA_SHARED, false);
                }
                else
                {
                    LOG_MOUNT("MassStorageStateChanged requesting unmount\n");
                    // need to successfully unmount first
                    RequestUnmount(mp, kUnmountingForUms);