Android5.0挂载NTFS为只读问题

一、问题描述

连接两个u盘；一个为NTFS，一个为FAT32；从NTFS可以向FAT32拷贝，反之报错“只读文件系统”。

二、问题原因

mount

/dev/block/vold/8:1 /mnt/usb/843E1E3A3E1E2628 ntfs ro,dirsync,nosuid,nodev,noexec,relatime,uid=1023,gid=1023,umask=02,nls=utf8,errors=continu
e,mft_zone_multiplier=1 0 0

ll /mnt/usb/

dr-xr-xr-x media_rw media_rw          2015-04-03 14:23 843E1E3A3E1E2628

问题有两个：

1.NTFS格式U盘挂载为READONLY；

2.挂载点目录权限问题

三、问题解决

1.修复问题1

移植fstype_support/android_external_ntfs-3g，使用ntfs-3g挂载。

NTFS_3G文件系统支持包

system/vold/Ntfs.cpp

#define  NTFS_3G_PATH  "/system/bin/ntfs-3g" //add by tank
int Ntfs::doMount(const char *fsPath, const char *mountPoint,
                 bool ro, bool remount, int ownerUid, int ownerGid,
                 int permMask) {
    int rc;
    unsigned long flags;
    char mountData[255];

    flags = MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_DIRSYNC;

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

#if 0
    char value[PROPERTY_VALUE_MAX];
    property_get("persist.sampling_profiler", value, "");
    if (value[0] == '1') {
        SLOGW("The SD card is world-writable because the"
            " 'persist.sampling_profiler' system property is set to '1'.");
        permMask = 0;
    }

    sprintf(mountData,
            "uid=%d,gid=%d,fmask=%o,dmask=%o,nls=utf8",
            ownerUid, ownerGid, permMask, permMask);

    rc = mount(fsPath, mountPoint, "ntfs3g", flags, mountData);
#else
    SLOGI("mount ntfs block device by tcl ntfs ntfs-3g");
    sprintf(mountData,"locale=utf8,uid=%d,gid=%d,fmask=%o,dmask=%o,inherit, atime",\
                        ownerUid, ownerGid, permMask, permMask);
    const char *args[16];
    args[0] = NTFS_3G_PATH;
    args[1] = fsPath;
    args[2] = mountPoint;
    args[3] = "-o";
    args[4] = mountData;
    args[5] = NULL;
    rc = logwrap(5, args, 1);
#endif
    if (rc) {
        SLOGE("%s appears to be a read only filesystem - retrying mount RO", fsPath);
        flags |= MS_RDONLY;
        rc = mount(fsPath, mountPoint, "ntfs", flags, mountData);
    }

    return rc;
}

2.修复问题2

system/vold/Volume.cpp

int Volume::mountVol() {
  if (isFatFs) {
    if (Fat::doMount(devicePath, getMountpoint(), false, false, false,
                /*AID_MEDIA_RW*/AID_SYSTEM, /*AID_MEDIA_RW*/AID_SDCARD_RW, /*permMask*/0002, true)) { //modify by tank
      SLOGE("%s failed to mount via VFAT (%s)\n", devicePath, strerror(errno));
      isFatFs = false;
    } else {
      isExtFs = false;
      isExfatFs = false;
    }
  }
}