android中system/etc/vold.fstab文件疑惑

## 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
dev_mount sdcard /mnt/sdcard 3 /devices/platform/mmci-omap-hs.0/mmc_host/mmc0

## 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


以上代码为android文件系统：android_fs里面的system/etc/vold.fstab的全部内容，其中实际上也只有如下一行其他为注释：
  dev_mount sdcard /mnt/sdcard 3 /devices/platform/mmci-omap-hs.0/mmc_host/mmc0
我知道这个是类似pc机上的开机自动挂载分区的配置文件，但是这个看不懂，请详细解释一下这几个的作用和代表的意思：
  (1) dev_mount sdcard  
  (2) /sdcard 2  
  (3) /devices/platform/goldfish_mmc.0 
  (4) /devices/platform/msm_sdcc.2/mmc_host/mmc1

(2) /sdcard 2  
  挂载点
  (3) /devices/platform/goldfish_mmc.0  
  (4) /devices/platform/msm_sdcc.2/mmc_host/mmc1
  设备文件名称， 第一个应该时模拟器的sd设备文件， 第二个时msm芯片sd设备的名称吧