如何让安卓挂载 EXT4 格式的 SD 卡？

突发奇想，既然内核支持 EXT4 ，为什么不把外置储存卡格式化成 EXT4 ？我把 SD 卡格式化成 EXT4 后插入手机，结果提示 SD 卡受损，必须重新格式化。

shell@android:/ $ mount
rootfs / rootfs ro,relatime 0 0
tmpfs /dev tmpfs rw,nosuid,relatime,mode=755 0 0
devpts /dev/pts devpts rw,relatime,mode=600 0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,relatime 0 0
none /acct cgroup rw,relatime,cpuacct 0 0
tmpfs /mnt/secure tmpfs rw,relatime,mode=700 0 0
tmpfs /mnt/asec tmpfs rw,relatime,mode=755,gid=1000 0 0
tmpfs /mnt/obb tmpfs rw,relatime,mode=755,gid=1000 0 0
none /dev/cpuctl cgroup rw,relatime,cpu 0 0
/emmc@android /system ext4 ro,noatime,noauto_da_alloc,commit=1,data=ordered 0 0
/emmc@usrdata /data ext4 rw,nosuid,nodev,noatime,discard,noauto_da_alloc,data=ordered 0 0
/emmc@cache /cache ext4 rw,nosuid,nodev,noatime,discard,noauto_da_alloc,data=ordered 0 0
/dev/block/loop0 /mnt/cd-rom iso9660 ro,relatime 0 0
/emmc@protect_f /protect_f ext4 rw,nosuid,nodev,noatime,nodelalloc,noauto_da_alloc,commit=1,data=ordered 0 0
/emmc@protect_s /protect_s ext4 rw,nosuid,nodev,noatime,nodelalloc,noauto_da_alloc,commit=1,data=ordered 0 0
/dev/block/vold/179:8 /storage/sdcard1 vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0

外置的 SD 卡应给是 /dev/block/vold/179:7 ，看得出没有挂载。

查看 vold.fstab

shell@android:/ $ cat /system/etc/vold.fstab
## Vold 2.0 Generic fstab
## - San Mehat ([email protected])
##

#######################
## Regular device mount
##
## Format: dev_mount <label> <mount_point> <part> <sysfs_path1...>
## label - Label for the volume
## mount_point - Where the volume will be mounted
## part - Partition # (1 based), or 'auto' for first usable partition.
## <sysfs_path> - List of sysfs paths to source devices
######################

## Example of a standard sdcard mount for the emulator / Dream
# Mounts the first usable partition of the specified device --phone: sdcard2(path: /storage/sdcard1); external sd card: sdcard(path: /storage/sdcard0)
dev_mount sdcard2 /storage/sdcard1 emmc@fat /devices/platform/goldfish_mmc.0 /devices/platform/mtk-msdc.0/mmc_host
dev_mount sdcard /storage/sdcard0 auto /devices/platform/goldfish_mmc.1 /devices/platform/mtk-msdc.1/mmc_host
## Example of a dual card setup
# dev_mount left_sdcard /mnt/sdcard1 auto /devices/platform/goldfish_mmc.0 /devices/platform/mtk-sd.0/mmc_host/mmc0
# dev_mount right_sdcard /mnt/sdcard2 auto /devices/platform/goldfish_mmc.1 /devices/platform/mtk-sd.2/mmc_host/mmc2

## Example of specifying a specific partition for mounts
# dev_mount sdcard /mnt/sdcard 2 /devices/platform/goldfish_mmc.0 /devices/platform/msm_sdcc.2/mmc_host/mmc1


这该怎么改呢，才能实现自动挂载 EXT4 ？