Android下开机启动后U盘经常不能自动挂载

原因大致为状态机混乱：

Initializing No-Media Idle-Unmounted Pending Mounted Unmounting Checking Formatting Shared-Unmounted Shared-Mounted Unknown-Error

一、问题描述

挂U盘开机正常；开机后挂U盘不正常。经常出现状态混乱。

二、正确流程

1.挂载

D/Vold    ( 1148): Volume 1214-9D53 state changing -1 (Initializing) -> 0 (No-Media)
D/Vold    ( 1148): Volume 1214-9D53 state changing 0 (No-Media) -> 1 (Idle-Unmounted)
D/Vold    ( 1148): Volume 1214-9D53 state changing 1 (Idle-Unmounted) -> 3 (Checking)
D/Vold    ( 1148): Volume 1214-9D53 state changing 3 (Checking) -> 4 (Mounted)

2.卸载

D/Vold    ( 1148): Volume 1214-9D53 state changing 4 (Mounted) -> 5 (Unmounting)
D/Vold    ( 1148): Volume 1214-9D53 state changing 5 (Unmounting) -> 1 (Idle-Unmounted)
D/Vold    ( 1148): Volume 1214-9D53 state changing 1 (Idle-Unmounted) -> 0 (No-Media)

MountService启动：

private void readStorageListLocked();

3.MountService启动时U盘已经挂上

D/MountService( 2044): got storage path: null description: SD卡 primary: false removable: false emulated: true mtpReserve: 0 allowMassStorage: false maxFileSize: 0
D/MountService( 2044): addVolumeLocked() StorageVolume:
D/MountService( 2044):     mStorageId=65537 mPath=/storage/emulated/0 mDescriptionId=17040783 
D/MountService( 2044):     mPrimary=true mRemovable=false mEmulated=true mMtpReserveSpace=0 
D/MountService( 2044):     mAllowMassStorage=false mMaxFileSize=0 mOwner=UserHandle{0} mUuid=null 
D/MountService( 2044):     mUserLabel=null mState=null 
D/MountService( 2044): got storage path: /mnt/sdcard description: SD卡 primary: true removable: false emulated: false mtpReserve: 0 allowMassStorage: false maxFileSize: 0
D/MountService( 2044): addVolumeLocked() StorageVolume:
D/MountService( 2044):     mStorageId=0 mPath=/mnt/sdcard mDescriptionId=17040783 mPrimary=true 
D/MountService( 2044):     mRemovable=true mEmulated=false mMtpReserveSpace=0 mAllowMassStorage=false 
D/MountService( 2044):     mMaxFileSize=0 mOwner=null mUuid=null mUserLabel=null mState=null 
D/MountService( 2044): got storage path: null description: USB存储器 primary: false removable: false emulated: false mtpReserve: 0 allowMassStorage: false maxFileSize: 0
I/MountService( 2044): Updating valid state unmounted
D/MountService( 2044): addVolumeLocked() StorageVolume:
D/MountService( 2044):     mStorageId=0 mPath=/mnt/usb/1214-9D53 mDescriptionId=17040784 
D/MountService( 2044):     mPrimary=false mRemovable=true mEmulated=false mMtpReserveSpace=0 
D/MountService( 2044):     mAllowMassStorage=false mMaxFileSize=0 mOwner=null mUuid=null 
D/MountService( 2044):     mUserLabel=null mState=null 
D/MountService( 2044): volume state changed for /mnt/usb/1214-9D53 (removed -> unmounted)
W/MountService( 2044): getSecureContainerList() called when storage not mounted
W/MountService( 2044): getSecureContainerList() called when storage not mounted
I/MountService( 2044): doMountVolume: Mouting /mnt/sdcard
E/MountService( 2044): Boot-time mount failed (-1)
I/MountService( 2044): doMountVolume: Mouting /mnt/usb/1214-9D53

4.MountService启动时U盘没有挂上

D/MountService( 2015): got storage path: null description: SD卡 primary: false removable: false emulated: true mtpReserve: 0 allowMassStorage: false maxFileSize: 0
D/MountService( 2015): addVolumeLocked() StorageVolume:
D/MountService( 2015):     mStorageId=65537 mPath=/storage/emulated/0 mDescriptionId=17040783 
D/MountService( 2015):     mPrimary=true mRemovable=false mEmulated=true mMtpReserveSpace=0 
D/MountService( 2015):     mAllowMassStorage=false mMaxFileSize=0 mOwner=UserHandle{0} mUuid=null 
D/MountService( 2015):     mUserLabel=null mState=null 
D/MountService( 2015): got storage path: /mnt/sdcard description: SD卡 primary: true removable: false emulated: false mtpReserve: 0 allowMassStorage: false maxFileSize: 0
D/MountService( 2015): addVolumeLocked() StorageVolume:
D/MountService( 2015):     mStorageId=0 mPath=/mnt/sdcard mDescriptionId=17040783 mPrimary=true 
D/MountService( 2015):     mRemovable=true mEmulated=false mMtpReserveSpace=0 mAllowMassStorage=false 
D/MountService( 2015):     mMaxFileSize=0 mOwner=null mUuid=null mUserLabel=null mState=null 
D/MountService( 2015): got storage path: null description: USB存储器 primary: false removable: false emulated: false mtpReserve: 0 allowMassStorage: false maxFileSize: 0
W/MountService( 2015): getSecureContainerList() called when storage not mounted
W/MountService( 2015): getSecureContainerList() called when storage not mounted
I/MountService( 2015): doMountVolume: Mouting /mnt/sdcard
E/MountService( 2015): Boot-time mount failed (-1)
W/MountService( 2015): Duplicate state transition (mounted -> mounted) for /storage/emulated/0

三、问题解决

该问题不是逻辑问题；而是creash问题。

后来发现公司添加一个新增接口，对指针没有做判断；存在野指针问题，同时没有在析构函数中做指针为null的free判断，导致vold进程不定时creash、导致mount状态混乱。

通过在free后至null、解决野指针问题；在析构函数中做null判断，显示调用free后；问题解决。