通过adb修改Android etc下的vold.fstab，调测vold.fstab

一、修改vold.fstab

/etc link到system/etc，需要修改/etc/vold.fstab，但vold.fstab为只读，在命令行下无法修改

使用adb来实现更改的目的，步骤：

1. 获取root权限，adb root（若终端上后台有运行adbd，则插上usb至PC时，终端命令行下会打印出android_usb gadget: high speed config #1: android）

2. 更改system为读写，adb remount（此命令后，终端命令行下会打印EXT4-fs (mmcblk0p2): re-mounted. Opts: (null)）

3. 通过adb下载/system/etc/vold.fstab到PC本地，adb pull /system/etc/vold.fstab vold.fstab

4. 在PC本地修改vold.fstab

5. 通过adb上传vold.fstab至终端/system/etc目录，adb push vold.fstab /system/etc/vold.fstab

以上则可完成后，重启即可见到修改后的效果

二、调测vold.fstab

调试自动加载U盘时，需要配置vold.fstab，原来的vold.fstab如下：

## Vold 2.0 Generic fstab
## - San Mehat ([e-mail])
## 
#######################
## Regular device mount
##
## Format: dev_mount  
## label        - Label for the volume
## mount_point  - Where the volume will be mounted
## part         - Partition # (1 based), or 'auto' for first usable partition.
## - 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
dev_mount sdcard /mnt/sdcard auto /devices/platform/mxsdhci.0/mmc_host/mmc1
#used for usb host
dev_mount udisk /mnt/udisk auto /devices/platform/fsl-ehci.0/usb

## Example of a dual card setup
# dev_mount left_sdcard  /sdcard1  auto /devices/platform/goldfish_mmc.0 /devices/platform/msm_sdcc.2/mmc_host/mmc1
# dev_mount right_sdcard /sdcard2  auto /devices/platform/goldfish_mmc.1 /devices/platform/msm_sdcc.3/mmc_host/mmc1

## Example of specifying a specific partition for mounts
# dev_mount sdcard /sdcard 2 /devices/platform/goldfish_mmc.0 /devices/platform/msm_sdcc.2/mmc_host/mmc1
只针对usb部分修改，由于手里的板子上需要两个usb host，实际实际中使用fsl-ehci.0/usb1和fsl-ehci.0/usb2，所以加入下面两行：

dev_mount disk /data/udisk auto /devices/platform/fsl-ehci.0/usb1
dev_mount udisk /mnt/udisk auto /devices/platform/fsl-ehci.1/usb2

(PS:手动加载在命令行下直接运行mount -t vfat /dev/block/sda1 /mnt/udisk -o rw,dmask=0000,fmask=0000,noatime)
这样，分别插入两个usb端口后，使用mount查看到自动mount的节点，如下：

rootfs / rootfs ro,relatime 0 0
tmpfs /dev tmpfs rw,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
tmpfs /sqlite_stmt_journals tmpfs rw,relatime,size=4096k 0 0
none /acct cgroup rw,relatime,cpuacct 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
tmpfs /mnt/shm tmpfs rw,relatime,size=1024k,mode=775,uid=1000,gid=1003 0 0
none /dev/cpuctl cgroup rw,relatime,cpu 0 0
/dev/block/mmcblk0p2 /system ext4 ro,relatime,barrier=1,data=ordered 0 0
/dev/block/mmcblk0p5 /data ext4 rw,nosuid,nodev,relatime,barrier=1,nodelalloc,data=ordered 0 0
/dev/block/mmcblk0p6 /cache ext4 rw,nosuid,nodev,relatime,barrier=1,data=ordered 0 0
/dev/block/mmcblk0p7 /auth ext4 rw,relatime,barrier=1,data=ordered 0 0
/dev/block/mmcblk0p8 /soft ext4 rw,relatime,barrier=1,data=ordered 0 0
/dev/block/mmcblk0p11 /inand vfat rw,relatime,fmask=0000,dmask=0000,allow_utime=0022,codepage=cp437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro 0 0

/dev/block/vold/8:1 /mnt/udisk vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0002,dmask=0002,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0

/dev/block/vold/8:1 /data/udisk vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0002,dmask=0002,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0

注意：可能由于system/bin/vold的bebug，如果同时mount两个节点于同一个目录，好像只能自动加载第一个mount点，而第二个节点没法自动加载