File changes do not always sync

[alpgarcia]

When a file is modified either in the sd card or in the userdata partition, changes are not always persisted.

As a workaround, forcing sync explicitly works.

It is worth exploring whether the filesystems are mounted using the sync flag and if they aren't, test whether it could solve the problem without affecting performance.

[alpgarcia]

I did some tests. I added the following script to the sd card: create_files.sh:

#!/bin/sh

for i in 1 2 3 4 5; do
  echo ${i} >> ${i}
done

The test consisted of the following steps:

1. Power on the console.
2. cd /sdcard
3. ./created_files.sh
4. Check the files with ls and cat.
5. Power off via button.
6. Power on the console again.
7. cd /sdcard
8. Check the files with ls and cat.
9. Reset the test, rm 1 2 3 4 5 (or whatever files were actually created).
10. Power off the console.

I repeated it 5 times. Step 4 always returned 5 files with their expected content. Step 8 returned a different set of unexpected results:

• 3 times the 5 files were there, but empty.
• 1 time only one file remained there, and it was empty.
• Once all the files were there with the expected content.

Then, I did the same but instead of powering off via button in step 5, I powered off the console via poweroff command. Again 5 times:

• 5 times all the files were there with the expected content.
• I executed it a 6th time skipping step 4 and worked well too.

At this point seems to be clear that poweroff command works as expected and the buffers are flushed during the shutdown process.

Next test was repeating the same initial steps as described above, but adding the following one before step 2:

1. Power on the console. 1.1. mount -o remount,sync /mnt/sdcard/
2. cd /sdcard
3. ./created_files.sh
4. Check the files with ls and cat.
5. Power off via button.
6. Power on the console again.
7. cd /sdcard
8. Check the files with ls and cat.
9. Reset the test, rm 1 2 3 4 5 (or whatever files were actually created).
10. Power off the console.

The results were:

• 5 times the files were there with the expected content.

So the next steps are:

• Mount the filesystems (sd card and userdata) with the sync flag.
• Add the poweroff command when exiting RetroArch, this way we make sure there is a proper way of triggering an ordered shutdown.
• Test, test, and test again to see if there is any noticeable performance loss due to the sync flag.