[Moto E6 Questions & Answers] gwgw:
It happens on my XT2005-5, as well.

Once the file is gone, I could not make any other file, either.

Right after mounting:

surfna:/ # ls -altr /oem

total 52

drwxr-xr-x 21 root root 4096 2009-01-01 01:00 ..

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 usc

-rw-r--r-- 1 root root 272 2021-01-27 16:15 oem.prop

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 comcast

drwxr-xr-x 9 root root 4096 2021-01-27 16:16 .

drwxr-xr-x 6 root root 4096 2021-01-27 16:16 app

drwxr-xr-x 7 root root 4096 2021-01-27 16:16 overlay

drwxr-xr-x 12 root root 4096 2021-01-27 16:16 priv-app

drwxr-xr-x 7 root root 4096 2021-01-27 16:17 etc

drwx------ 2 root root 16384 2021-01-27 16:17 lost+found

Creating a file (TTT):

surfna:/ # touch /oem/TTT

surfna:/ # ls -altr /oem/

total 52

drwxr-xr-x 21 root root 4096 2009-01-01 01:00 ..

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 usc

-rw-r--r-- 1 root root 272 2021-01-27 16:15 oem.prop

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 comcast

drwxr-xr-x 6 root root 4096 2021-01-27 16:16 app

drwxr-xr-x 7 root root 4096 2021-01-27 16:16 overlay

drwxr-xr-x 12 root root 4096 2021-01-27 16:16 priv-app

drwxr-xr-x 7 root root 4096 2021-01-27 16:17 etc

drwx------ 2 root root 16384 2021-01-27 16:17 lost+found

-rw-r--r-- 1 root root 0 2021-05-30 03:58 TTT

drwxr-xr-x 9 root root 4096 2021-05-30 03:58 .

And it disappered:

surfna:/ # ls -altr /oem/

total 52

drwxr-xr-x 21 root root 4096 2009-01-01 01:00 ..

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 usc

-rw-r--r-- 1 root root 272 2021-01-27 16:15 oem.prop

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 comcast

drwxr-xr-x 6 root root 4096 2021-01-27 16:16 app

drwxr-xr-x 7 root root 4096 2021-01-27 16:16 overlay

drwxr-xr-x 12 root root 4096 2021-01-27 16:16 priv-app

drwxr-xr-x 7 root root 4096 2021-01-27 16:17 etc

drwx------ 2 root root 16384 2021-01-27 16:17 lost+found

drwxr-xr-x 9 root root 4096 2021-05-30 03:58 .

I did touch and then chmod 700, without error.

But no TTT. The time stamp of oem stayed unchanged.

surfna:/ # touch /oem/TTT

surfna:/ # chmod 700 /oem/TTT

surfna:/ # ls -altr /oem/

total 52

drwxr-xr-x 21 root root 4096 2009-01-01 01:00 ..

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 usc

-rw-r--r-- 1 root root 272 2021-01-27 16:15 oem.prop

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 comcast

drwxr-xr-x 6 root root 4096 2021-01-27 16:16 app

drwxr-xr-x 7 root root 4096 2021-01-27 16:16 overlay

drwxr-xr-x 12 root root 4096 2021-01-27 16:16 priv-app

drwxr-xr-x 7 root root 4096 2021-01-27 16:17 etc

drwx------ 2 root root 16384 2021-01-27 16:17 lost+found

drwxr-xr-x 9 root root 4096 2021-05-30 03:58 .

Same thing, but without delay. No effect.

surfna:/ # touch /oem/TTT; chmod 700 /oem/TTT

surfna:/ # ls -altr /oem/

total 52

drwxr-xr-x 21 root root 4096 2009-01-01 01:00 ..

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 usc

-rw-r--r-- 1 root root 272 2021-01-27 16:15 oem.prop

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 comcast

drwxr-xr-x 6 root root 4096 2021-01-27 16:16 app

drwxr-xr-x 7 root root 4096 2021-01-27 16:16 overlay

drwxr-xr-x 12 root root 4096 2021-01-27 16:16 priv-app

drwxr-xr-x 7 root root 4096 2021-01-27 16:17 etc

drwx------ 2 root root 16384 2021-01-27 16:17 lost+found

drwxr-xr-x 9 root root 4096 2021-05-30 03:58 .

Trying to create more files ==> I/O error.

surfna:/ # touch /oem/TTT2

touch: '/oem/TTT2': I/O error

1|surfna:/ # touch /oem/123

touch: '/oem/123': I/O error

Repeating same thing. This time, time stamp of oem changed!

surfna:/ # touch /oem/TTT23

touch: '/oem/TTT23': I/O error

1|surfna:/ # touch /oem/TTT23

surfna:/ # touch /oem/T12

touch: '/oem/T12': I/O error

1|surfna:/ # touch /oem/TDD

touch: '/oem/TDD': I/O error

1|surfna:/ # ls -altr /oem/

total 52

drwxr-xr-x 21 root root 4096 2009-01-01 01:00 ..

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 usc

-rw-r--r-- 1 root root 272 2021-01-27 16:15 oem.prop

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 comcast

drwxr-xr-x 6 root root 4096 2021-01-27 16:16 app

drwxr-xr-x 7 root root 4096 2021-01-27 16:16 overlay

drwxr-xr-x 12 root root 4096 2021-01-27 16:16 priv-app

drwxr-xr-x 7 root root 4096 2021-01-27 16:17 etc

drwx------ 2 root root 16384 2021-01-27 16:17 lost+found

drwxr-xr-x 9 root root 4096 2021-05-30 04:03 .

Using echo instead of touch to create a file.

Error for TDD, but no error for TTT, the original file, somehow.

But it doesn't show up is ls.

surfna:/ # echo 123 > /oem/TDD

/system/bin/sh: can't create /oem/TDD: I/O error

1|surfna:/ # echo 123 > /oem/TTT

surfna:/ # ls -altr /oem/

total 52

drwxr-xr-x 21 root root 4096 2009-01-01 01:00 ..

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 usc

-rw-r--r-- 1 root root 272 2021-01-27 16:15 oem.prop

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 comcast

drwxr-xr-x 6 root root 4096 2021-01-27 16:16 app

drwxr-xr-x 7 root root 4096 2021-01-27 16:16 overlay

drwxr-xr-x 12 root root 4096 2021-01-27 16:16 priv-app

drwxr-xr-x 7 root root 4096 2021-01-27 16:17 etc

drwx------ 2 root root 16384 2021-01-27 16:17 lost+found

drwxr-xr-x 9 root root 4096 2021-05-30 04:03 .

But it shows up with full path.

surfna:/ # ls -altr /oem/TTT

-rwx------ 1 root root 4 2021-05-30 04:03 /oem/TTT

I rebooted (recoverly) and checked original mount parameters.

surfna:/ # mount |grep oem

/dev/block/dm-1 on /oem type ext4 (ro,context=u:object_r:oemfs:s0,nosuid,nodev,relatime,block_validity,delalloc,barrier,user_xattr)

Remounting as "rw" doesn't change other parameters.

surfna:/ # mount -o rw,remount /oem

surfna:/ # mount |grep oem

/dev/block/dm-1 on /oem type ext4 (rw,context=u:object_r:oemfs:s0,nosuid,nodev,relatime,block_validity,delalloc,barrier,user_xattr)

This time, the file didn't stay.

surfna:/ # touch /oem/TTT;chmod 700 /oem/TTT;ls -altr /oem/;mount |grep oem

total 52

drwxr-xr-x 21 root root 4096 2009-01-01 01:00 ..

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 usc

-rw-r--r-- 1 root root 272 2021-01-27 16:15 oem.prop

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 comcast

drwxr-xr-x 6 root root 4096 2021-01-27 16:16 app

drwxr-xr-x 7 root root 4096 2021-01-27 16:16 overlay

drwxr-xr-x 12 root root 4096 2021-01-27 16:16 priv-app

drwxr-xr-x 7 root root 4096 2021-01-27 16:17 etc

drwx------ 2 root root 16384 2021-01-27 16:17 lost+found

drwxr-xr-x 9 root root 4096 2021-05-30 04:40 .

/dev/block/dm-1 on /oem type ext4 (rw,context=u:object_r:oemfs:s0,nosuid,nodev,relatime,block_validity,delalloc,barrier,user_xattr)

But it's there when I used full path, again.

surfna:/ # touch /oem/TTT;chmod 700 /oem/TTT;ls -altr /oem/TTT ;mount |grep oem

-rwx------ 1 root root 0 2021-05-30 04:41 /oem/TTT

Writing to the file did not change the time stamp of oem, but touching it changed.

surfna:/ # touch /oem; ls -altr /oem/

total 52

drwxr-xr-x 21 root root 4096 2009-01-01 01:00 ..

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 usc

-rw-r--r-- 1 root root 272 2021-01-27 16:15 oem.prop

drwxr-xr-x 3 root root 4096 2021-01-27 16:15 comcast

drwxr-xr-x 6 root root 4096 2021-01-27 16:16 app

drwxr-xr-x 7 root root 4096 2021-01-27 16:16 overlay

drwxr-xr-x 12 root root 4096 2021-01-27 16:16 priv-app

drwxr-xr-x 7 root root 4096 2021-01-27 16:17 etc

drwx------ 2 root root 16384 2021-01-27 16:17 lost+found

drwxr-xr-x 9 root root 4096 2021-05-30 04:53 .

It's a block device (rw) and special block.

It's small. Too small to contain all directories.

surfna:/ # ls -al /dev/block/dm-1

brw------- 1 root root 252, 1 1970-01-27 08:20 /dev/block/dm-1

surfna:/ # file /dev/block/dm-1

/dev/block/dm-1: block special