如何安装允许读取和写入任何应用程序的TMPFS目录？ （root可用） -- storage 领域 和 permissions 领域 和 mount 领域 和 magisk 领域 和 selinux 领域 android 相关 的问题

I am trying to create some volatile (tmpfs) storage for my Android, to avoid clutter.

I am trying to follow the previous questions:

making manually mounted partition folders write accessible to all apps

and

How to bind mount a folder inside /sdcard with correct permissions?

The way I am doing is by adding an "init script" into a magisk "service.d" directory:

# cat /sbin/.magisk/img/.core/service.d/001-tmpfs.sh                               #!/system/bin/sh while [ "$(getprop sys.boot_completed)" != 1 ]; do   sleep 1 done  su -mm -c mount -v none -t tmpfs -o size=4g,nosuid,nodev,noexec,noatime,context=u:object_r:sdcardfs:s0,uid=0,gid=9997,mode=0777 /mnt/runtime/write/emulated/0/Download/tmpfs-cleared-on-reboot  

Seems plain and simple, only doesn't work in the sense that the folder is mounted successfully, and files disappear after a reboot, if copied there by root. But an ordinary app cannot copy anything there. FX Explorer, for example, says "Access was denied."

It does work though if I set setenforce 0, which seems to indicate that there is a SELinux problem.

The only relevant error in dmesg looks the following:

[ 3181.763111] [20200731_13:36:57.002188]@1 type=1400 audit(1596173815.897:12245): avc: denied { create } for pid=5870 comm="Thread-139" name=233339202D5370656E63657220477265656E62657267206F6E20696E7472696E7369632076732E20696E737472756D656E74616C2076616C7565732C206F766572636F6E666964656E63652C20616E6420686F7720746F2061637475616C6C79207570646174652062656C6965667320696D70726F76656420617564696F2E6D7033 scontext=u:r:untrusted_app:s0:c104,c256,c512,c768 tcontext=u:object_r:sdcardfs:s0 tclass=file permissive=0 

It appears if I try to copy some file into this directory.

ls -lahZ /mnt/runtime/write/emulated/0/Download/ gives

drwxrwxrwx   2 root everybody u:object_r:sdcardfs:s0   40 2020-07-31 13:25 tmpfs-cleared-on-reboot 

ls -larhtZ /storage/emulated/0/Download/

drwxrwxrwx   2 root everybody u:object_r:sdcardfs:s0   40 2020-07-31 13:25 tmpfs-cleared-on-reboot 

Which is strange, because the other files in the directory have permissions like this:

drwxrwx--x   2 root sdcard_rw u:object_r:sdcardfs:s0 4.0K 2020-07-30 20:04 pdfs-scientific_papers-toread 

the group is different. I am not sure whether this is related or not.

But anyway, I cannot copy anything into this directory as a normal app.

I can copy stuff there as root, and it disappears on reboot, as expected. But where is the permissions problem?

This is Android 9 on OnePlus 5t.