Android recognition/mounting of USB flash drives

The author directly mounted the USB flash drive to the SD card. My machine is a MTK6575 platform that supports sdcard and sdcard2. You can manually mount the USB flash disk to sdcard2 to identify the USB flash disk, but this is only a temporary solution, because sdcard2 and usb may conflict with each other. For example, if two devices have files of the same name in the same directory, only one file can be identified.
To mount a USB flash drive, you need to modify several files:

1. Modify vold. fstab
Add a dev_mount udisk/mnt/udisk auto/devices/platform/mt_usb/usb1
Ii. Modify init. rc
1,
In
# Create mountpoints
Add one
Mkdir/mnt/udisk 0076 system
2,
In
# Backwards Compat
Add one
Symlink/mnt/udisk
3. Modify storage_list.xml. This file is called in the readStorageList method of frameworks/base/services/java/com/android/server/MountService. java.

[Java]
Private void readStorageList (Resources resources ){
MVolumes. clear ();
MVolumeMap. clear ();
Int id = com. android. internal. R. xml. storage_list;
XmlResourceParser parser = resources. getXml (id );
AttributeSet attrs = Xml. asAttributeSet (parser );
// Storage_list.xml will be parsed here, and the device path (such as "mnt/sdcard") of the external storage room will be broadcast to the upper layer, after receiving the broadcast, the upper layer scans the device based on the path.
...
}

The storage_list.xml file that comes with the system is in the frameworks/base/core/res/xml directory. The content is as follows:
[Html]
<StorageList xmlns: android = "http://schemas.android.com/apk/res/android">
<! -- Removable is not set in nosdcard product -->
<Storage android: mountPoint = "/mnt/sdcard"
Android: storageDescription = "@ string/storage_sd_card"
Android: removable = "true"
Android: primary = "true"/>
 
</StorageList>
For the first time, I added
[Html]
<Storage android: mountPoint = "/mnt/udisk"
Android: storageDescription = "@ string/storage_sd_card"
Android: removable = "true"
Android: primary = "false"/>
The test is invalid after re-compilation. Because MTK platform code is used, storage_list.xml may be overwritten by MTK code. Therefore, storage_list.xml is searched in the source code and found in the following directory.
./Mediatek/custom/{project name}/resource_overlay/generic/frameworks/base/core/res/xml/storage_list.xml

./Mediatek/custom/{project name}/resource_overlay/generic_emmc/frameworks/base/core/res/xml/storage_list.xml

./Mediatek/custom/{project name}/resource_overlay/generic_nand/frameworks/base/core/res/xml/storage_list.xml
For the sake of security, I added the following code to these three files:
[Html]
<Storage android: mountPoint = "/mnt/udisk"
Android: storageDescription = "@ string/storage_usb"
Android: removable = "true"
Android: primary = "false"/>
After you try again, you can identify the USB flash drive. There will be some differences in the modification methods of different platforms. The method here is for reference only.