Android 技术专题系列之十七 －－ volume 服务

Android 的volume服务主要是用来管理usb/sd卡 等外部存储设备。平台可以对外部存储设备进行操作和轮询状态，当外部存储设备状态发生变化时，volume 服务也会即时报告平台。

相关代码主要位于：
system/core/vold
frameworks/base/services/java/com/android/server/MountListener.java
frameworks/base/services/java/com/android/server/MountService.java
frameworks/base/core/java/android/os/IMountService.aidl
hardware/libhardware_legacy/mount/IMountService.cpp
hardware/libhardware_legacy/include/hardware_legacy/IMountService.h

下图概述了这些组件之间的关系。但是没有搞清楚IMountService.h/cpp是干什么用的。

还有一点值得注意，MountService被一个Android内部类ServiceManager注册(SystemServer.java):
ServiceManager.addService("mount", new MountService(context))
以这种方式注册有名服务（named service），所注册的服务是一个实现了aidl产生的stub类的派生类，并不需要实现一个Service的派生类。ServiceManager仅供Android平台内部使用。

 

Rockie's Android Porting Guide（4）——Add SD card to your system Rockie Cheng Andorid use vold to manage SD card and it is easy to use. But I meet many troubles and finally find that the real problem is in the Linux Kernel. Thanks to the Android Mail List. Part I (kernel) (1)make sure thus kernel configuration in MMC driver CONFIG_MMC=y # CONFIG_MMC_DEBUG is not set CONFIG_MMC_UNSAFE_RESUME=y # CONFIG_MMC_EMBEDDED_SDIO is not set CONFIG_MMC_PARANOID_SD_INIT=y # # MMC/SD Card Drivers # CONFIG_MMC_BLOCK=y CONFIG_MMC_BLOCK_BOUNCE=y # CONFIG_MMC_BLOCK_PARANOID_RESUME is not set # CONFIG_SDIO_UART is not set # CONFIG_MMC_TEST is not set # # MMC/SD Host Controller Drivers # CONFIG_MMC_SDHCI=y (2)Disable this option  General Setup -> Create deprecated sysfs layout for older userspace tools Before I did this,vold showed a lot of trouble. And ,my media_path is not right  media_path /devices/platform/s3c-sdhci.0/mmc_host:mmc0<--my path before turn off that option media_path /devices/platform/s3c-sdhci.0/mmc_host/mmc0 <--this is the right one Vold may be unhappy to accept my old path,and it didn't work. D/vold    (   42): Accepted connection from framework D/vold    (   42): dispatch_cmd(send_ums_status): D/vold    (   42): dispatch_cmd(mount_volume:/sdcard): E/vold    (   42): Cannot start volume '/sdcard' (volume is not bound) D/MountListener(   59): handleEvent volume_nomedia:/sdcard D/MountListener(   59): handleEvent ums_disabled D/MountListener(   59): handleEvent ums_disconnected (3) rebuild your linux kernel PART II(android system) (1) creat a vold.conf in build/target/board/idea6410 ## vold configuration file for idea6410 volume_sdcard {     ## This is the direct uevent device path to the SD slot on the device media_path /devices/platform/s3c-sdhci.0/mmc_host/mmc0     media_type     mmc     mount_point    /sdcard     ums_path       /devices/platform/usb_mass_storage/lun0 } (2)add those below to AndroidBoard.mk include $(CLEAR_VARS) LOCAL_MODULE_CLASS := ETC LOCAL_MODULE := vold.conf LOCAL_SRC_FILES := $(LOCAL_MODULE) include $(BUILD_PREBUILT) (3)rebuild the system and check init.rc service vold /system/bin/vold     socket vold stream 0660 root mount (4)enjoy D/vold    (   42): Accepted connection from framework D/vold    (   42): dispatch_cmd(send_ums_status): D/vold    (   42): dispatch_cmd(mount_volume:/sdcard): I/vold    (   42): Evaluating dev '/devices/platform/s3c-sdhci.0/mmc_host/mmc0/mmc0:e624/block/mmcblk0' for mountable filesystems for '/sdcard' D/MountListener(   61): handleEvent volume_unmounted:/sdcard D/MountListener(   61): handleEvent ums_disabled D/MountListener(   61): handleEvent ums_disconnected D/MountListener(   61): handleEvent volume_checking:/sdcard   Rockie Cheng