Develop Reference

How to verify whether I could create a file in a specific folder or not on Android by C++\C?

At my first thought, I should know how to check the permissions of a folder in the Linux system(since the kernel of Android is linux) by C or C++.
Since C++17 is not available for me, so std::filesystem could not be used. And I searched on SO, I found access may be a solution. So I wrote the code snippet below:
if (access(folder_path, W_OK | X_OK) == 0) {
SDK_LOG_ERROR("folder is not writable");
}
But it seems not work as expected, I can manually create new files in a specific folder:
C:\tools>adb root
adbd is already running as root
C:\tools>adb remount
remount succeeded
C:\tools>adb shell
promotion:/system/etc/some_folder/.../config # ls -lhd .
drwxrwxrwx 2 root root 4.0K 2022-05-31 21:14 .
promotion:/system/etc/some_folder/.../config # touch a
promotion:/system/etc/some_folder/.../config # touch b
promotion:/system/etc/some_folder/.../config # ls -lh
total 14K
-rw-rw-rw- 1 root root 0 2022-05-31 21:14 a
-rw-rw-rw- 1 root root 0 2022-05-31 21:14 b
Before running the said code snippet, I call adb root; adb remount first, and then I call whoami in the terminal, the output is root.
But when I run the aforementioned code snippet on Android, the program tells me folder is not writable". What a surprise!

How to send HDMI-CEC commands from Amlogic 905x board to the TV using sysfs

I want to send raw HDMI-CEC commands (adb shell) from an Amlogic 905x ARM board (Android 6) to test the functionality. The board is rooted (tested, 'adb root' works) and connected to a TV with CEC capabilities (enabled, tested with video game console too).
First of all I want to clarify if the core functionality is built in, so I guess that if the right CEC command is sent to the right channel, I should notice a change of any kind to the TV set.
I want to test it at a lower abstraction level (sysfs i guess is ok and http://www.cec-o-matic.com/ is pretty straightforward on how to build the command strings) to avoid the complexity of a system library as of this step.
I noticed that some guys had positive results on turning the TV on, by using:
#echo 0x40 0x04 > /sys/class/cec/cmd
It didn't work on my end.
I think that I might have a different class file allocated for this purpose and I found '/sys/class/amhdmitx/amhdmitx0' which has a lot of endpoints/files that offers IO capabilities.
I got back from the device the details of the TV set connected to (EDID - Extended Display Identification Data), by using:
#cat /sys/class/amhdmitx/amhdmitx0/edid
That means there has to be a way to send commands to the TV too, like turning the TV on/off, changing source ...
Tried by sending to debug file because there is no cmd file available like in '/sys/class/cec/cmd':
#echo 0x40 0x04 > /sys/class/amhdmitx/amhdmitx0/debug
Does anyone know how can I do this, to test the sending procedure (device)-->(TV)?
Why there is no activity on the TV when using '/sys/class/cec/cmd'?
Which is the right file to use to send hex data to the TV?
The result of
cat /system/build.prop |grep hdmi && ls -l /dev/cec && ls -laht /sys/class/cec/ && settings list global |grep hdmi && echo 0x40 0x04 > /sys/class/cec/cmd && sleep 0.1 && cat /sys/class/cec/dump_reg && sleep 1 && cat /sys/class/cec/dump_reg
is
ro.sys.hdmiin.enable=true
mbx.hdmiin.switchfull=false
mbx.hdmiin.videolayer=false
ubootenv.var.hdmimode=
ro.hdmi.device_type=4
persist.sys.hdmi.keep_awake=false
crw-rw-rw- root root 222, 0 2014-12-31 16:00 cec
-r--r--r-- root root 4096 2018-05-08 08:47 arc_port
lrwxrwxrwx root root 2018-05-08 08:47 cec -> ../../devices/aocec/cec
--w------- root root 4096 2018-05-08 08:47 cmd
-rw-rw-r-- root root 4096 2018-05-08 08:47 dbg_en
-rw-rw-r-- root root 4096 2018-05-08 08:47 device_type
-r--r--r-- root root 4096 2018-05-08 08:47 dump_reg
-rw-rw-r-- root root 4096 2018-05-08 08:47 fun_cfg
-rw-rw-r-- root root 4096 2018-05-08 08:47 menu_language
-r--r--r-- root root 4096 2018-05-08 08:47 osd_name
-rw-rw-r-- root root 4096 2018-05-08 08:47 physical_addr
-r--r--r-- root root 4096 2018-05-08 08:47 port_num
-r--r--r-- root root 4096 2018-05-08 08:47 port_seq
-r--r--r-- root root 4096 2018-05-08 08:47 port_status
-rw-rw-r-- root root 4096 2018-05-08 08:47 vendor_id
-r--r--r-- root root 4096 2018-05-08 08:47 wake_up

Are you simply missing how to write to file? It is
echo "0x40 0x04" > /sys/class/cec/cmd
That works for me on s905x3 unit.

Managing files in Android terminal

Using a terminal emulator in my android phone I accidentally copied /proc directory into another user directory. Now I want to delete the copy but I don't have the permissions to do so. I tried to change ownership and permissions to 777 but with no success. I am using Oneplus 2 and termux application. Any suggestions?
Edit:
The original /proc directory :
dr-xr-xr-x 459 root root 0 Jan 1 1970 proc/
it was copied to /.../line/proc:
Line:
drwxrwxrwx 4 u0_a45 u0_a45 4096 Oct 17 12:23 line/
Line/proc:
dr-xr-xr-x 52 u0_a45 u0_a45 4096 Jan 1 1970
proc/
The new proc directories are not removable:
rm -rf line/proc
rm: can't remove 'line/proc/12159/task/12247': Permission denied
...

File not found in /data/media/0, but found in /storage/emulated/0

I use the smartphone emulator in Android Studio for a Nexus 4, API 23.
I took a picture through its camera, and I can check that the file is present at this different paths through the Android Device Monitor:
/data/media/0/DCIM/Camera/IMG_20160408_143726.jpg (rw-rw-r)
/storage/emulated/0/DCIM/Camera/IMG_20160408_143726.jpg (rw-rw)
Nevertheless, in my Activity I got different behaviors when I try to read the file:
new File("/data/media/0/DCIM/Camera/IMG_20160408_143726.jpg");
// isFile at false, canRead at false, length at 0
new File("/storage/emulated/0/DCIM/Camera/IMG_20160408_143726.jpg");
// isFile at true, canRead at true, length with a real value
Why is it so?

it depends on contructor, use this method to get the sdcard path instead, that will find the correct path for all devices
new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/DCIM/Camera/IMG_20160408_143726.jpg")

You probably would like to grant your app root permission so as to let it work properly. Take a look at this example:
u0_a1#android:/ $ toolbox ls -l /storage/emulated/0/UPDATE*
-rw-rw---- root sdcard_r 4997896 2016-09-08 20:08 UPDATE-SuperSU-v2.78.zip
u0_a1#android:/ $ toolbox ls -l /data/media/0/UPDATE*
/data/media/0/*: Permission denied
1|u0_a1#android:/ $ su
root#android:/ # toolbox ls -l /data/media/0/UPDATE*
-rw-rw-r-- media_rw media_rw 4997896 2016-09-08 20:08 UPDATE-SuperSU-v2.78.zip

Using ADB : How to get file modification date command

I have following command to get file date with time
adb shell ls -l /sdcard/sample.txt
Result of this command :
-rwxrwxr-x system sdcard_rw 676 2013-09-24 11:23 sample.txt
Now, I want 2013-09-24 11:23 time with seconds as well. like 2013-09-24 11:23:11
How I will get file modification date including seconds.
Thanks.. :)

If you have a stat command:
stat -c %y /sdcard/sample.txt
Seconds since Epoch
stat -c %Y /sdcard/sample.txt

By tweaking the code posted, I was able to get it worked using this command :
adb -d shell ls -l time-style="+%Y-%m-%d %H:%M:%S" path_to_file_in_device
The output is :
-rw-rw-r-- root sdcard_rw 22357385 2013-09-25 22:42 launcher.apk

ls -l --time-style="+%Y-%m-%d %H:%M:%S" /sdcard/sample.txt