How to mount a USB drive on Android Things? - linux

Question

I'm attempting to read files off of a USB drive for an Android Things app on a Raspberry Pi. I'm able to scan the list of mounted devices like so:
public static List<File> ScanForFiles(Context context){
ArrayList<File> files = new ArrayList<>();
try{
BufferedReader reader = new BufferedReader(new FileReader("/proc/self/mountinfo"));
String line;
while ((line = reader.readLine()) != null) {
String[] columns = line.split(" ");
Log.i(TAG, "Mounted: " + columns[4]);
//files.addAll(getListFiles(new File(columns[4])));
}
} catch (Exception ex){
ex.printStackTrace();
}
printFileInformation("/proc/partitions");
return files;
}
private static void printFileInformation(String fileName){
Log.i("TitanTV", "Reading contents of " + fileName);
try{
BufferedReader reader = new BufferedReader(new FileReader(fileName));
String line;
while ((line = reader.readLine()) != null){
Log.i("TitanTV", line);
}
} catch (Exception ex){
ex.printStackTrace();
}
}
Which displays the following output:
I: Mounted: /
I: Mounted: /dev
I: Mounted: /dev
I: Mounted: /dev/pts
I: Mounted: /dev/memcg
I: Mounted: /dev/cpuctl
I: Mounted: /proc
I: Mounted: /sys
I: Mounted: /sys/fs/selinux
I: Mounted: /sys/fs/pstore
I: Mounted: /acct
I: Mounted: /mnt
I: Mounted: /mnt/runtime/default/emulated
I: Mounted: /mnt/runtime/read/emulated
I: Mounted: /mnt/runtime/write/emulated
I: Mounted: /config
I: Mounted: /data
I: Mounted: /oem
I: Mounted: /gapps
I: Mounted: /storage
I: Mounted: /storage/emulated
I: Mounted: /storage/self
I: Reading contents of /proc/partitions
I: major minor #blocks name
I: 1 0 8192 ram0
I: 1 1 8192 ram1
I: 1 2 8192 ram2
I: 1 3 8192 ram3
I: 1 4 8192 ram4
I: 1 5 8192 ram5
I: 1 6 8192 ram6
I: 1 7 8192 ram7
I: 1 8 8192 ram8
I: 1 9 8192 ram9
I: 1 10 8192 ram10
I: 1 11 8192 ram11
I: 1 12 8192 ram12
I: 1 13 8192 ram13
I: 1 14 8192 ram14
I: 1 15 8192 ram15
I: 179 0 7761920 mmcblk0
I: 179 1 65536 mmcblk0p1
I: 179 2 1024 mmcblk0p2
I: 179 3 1024 mmcblk0p3
I: 179 4 32768 mmcblk0p4
I: 179 5 32768 mmcblk0p5
I: 179 6 524288 mmcblk0p6
I: 179 7 524288 mmcblk0p7
I: 179 8 64 mmcblk0p8
I: 179 9 64 mmcblk0p9
I: 179 10 1024 mmcblk0p10
I: 179 11 32768 mmcblk0p11
I: 179 12 32768 mmcblk0p12
I: 179 13 262144 mmcblk0p13
I: 179 14 262144 mmcblk0p14
I: 179 15 2683736 mmcblk0p15
I: 8 0 7847935 sda
I: 8 1 7845888 sda1
However, my thumb drive isn't apart of the list. So I'm guessing I need to mount it in some way. How can I mount the thumb drive and access the files on it?

Answer 1

ADB ONLY SOLUTION
Seem like as of now USB drives aren't mounted automatically. In order to make your code work I had to mount it manually.
As you can see (from /proc/partitions) in the /proc partition the USB drive is detected as sda.
ADB mounting
Make a directory to mount to
mkdir /mnt/usb
Mount the device
mount -t vfat -o rw /dev/block/sda1 /mnt/usb
Now you should be able to list (and manage) the files on the USB drive both via ADB and from within the app (/mnt/usb will also be logged).

Answer 2

I think the only solution is to create a service in init.rc to be able to execute the script with root permisions on Boot.
Apparently Android things doesnt have a solution right know.
Something like:
on property:dev.bootcomplete=1
start bootcomplete_handler
service bootcomplete_handler /system/bin/sh /system/bin/bc_handler.sh
class late_start
user root
group root
disabled
oneshot
But dont know if this will work

Answer 3

I have made an script that every 10 seconds if detects a usb storage units mounts it automatically, the only problem is to launch it on Boot, maybe this could help you, I have my post here:
Execute Script on Boot Android Things
And the script:
while true; do
if [ "$( ls -l /dev/block/sd* | wc -l)" -ge 1 ];
then echo "partition available"
if [ "$( mount | grep "usbAlv" -c)" -ge 1 ]; #if partition not mounted
then echo " Unit Mounted"
else
echo "not mounted"
//if folder where we mount the partition doesnt exist
if [ !"$( ls -l /sdcard/usbAlv | wc -l)" -ge 1 ];
then mkdir /sdcard/usbAlv
fi
su root << EOSU
mount -t vfat -o rw /dev/block/sd* /sdcard/usbAlv
EOSU
fi
else
echo "not partition available"
fi
sleep 10;
done
Hope it helps, i guess now is the only posible way to do it programatically

Answer 4

Working and discarded options
1. Use ADB (working)
As answerer by Onik in this post
2. Use USB API (working)
As Android API for USB allows bulkTransfer, you can code SCSI compatible commands.
You can also try existing libraries such as libaums, posted by Phaestion in response to this similar question
3. Inject shell commands at init.rc at boot.img (NOT working)
Shell commands can be injected to the init.rc file inside the boot.img (not the init.rc file that you can find in the /root directory). However, given the A-B boot nature of the AndroidThings compilation, I have been unable to make it work.
4. Add advanced app permissions (NOT working)
The following permissions seem promising to execute root commands from the app. However, permission denied error continues to block the root command execution.
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" tools:ignore="ProtectedPermissions" />
<uses-permission android:name="android.permission.CALL_PRIVILEGED" tools:ignore="ProtectedPermissions" />
<uses-permission android:name="android.permission.MOUNT_FORMAT_FILESYSTEMS" tools:ignore="ProtectedPermissions" />
<uses-permission android:name="android.permission.MANAGE_DEVICE_ADMINS" tools:ignore="ProtectedPermissions" />
<uses-permission android:name="android.permission.MANAGE_USB" tools:ignore="ProtectedPermissions" />
I even tried to compile an AndroidThings distribution with an app with such permissions but the Android Things console does NOT allow to include the app to the compilation
5. White list the app (NOT working)
There is a white list for priviledged apps. However, this white list is placed in a priviledged directory and cannot be overwritten even from the shell command with root user
6. Install the app at a priviledged location (NOT working)
Apps installed in priviledged directories can execute root commands. However, AndroidThings does NOT allow to install apps at such locations (even from the shell with root user)