File path selection based on newest inode

[X-Ryl669]

On the main page, there's a example with both A and B having a file called file7. From what I've observed, it seems mergerfs will select the file from the first listed filesystem. Is it possible to have it select the newest file (the one with the highest mtime?)

This would be useful for me in the following case:

1. Mergerfs is used to mount A and B filesystems in this order
2. B is a readonly filesystem that's updated on system upgrade, but A is a R/W filesystem used to store configuration files and modification made by the user.
3. Let's say there's a version 1.0 of a software in B, but a bug is found and the user install version 2.0 (that'll go to A). Later, the system is upgraded (B evolves) and the software in B is now version 3.0. I want the software from version 3.0 to be used, not the version in A that's listed first in the FS list of the mount command.
4. Notice that if we switch A and B (so that the readonly is listed first), the user can't use version 2.0 on B, since A will be selected first.

The policy "newest" is for selecting which filesystem to write to, not which to read from, right?

[trapexit]

https://trapexit.github.io/mergerfs/latest/config/functions_categories_policies/#policy-descriptions

The policy "newest" is for selecting which filesystem to write to, not which to read from, right?

1. mergerfs as explained in the docs is not an overlay filesystem. If you want to put "new files over old readonly ones" you should use overlayfs
2. No, open is a function with its own policy.

[trapexit]

As I said previously you set the open policy.

Also, in the example on the main page, if one delete file7, which is deleted? A ? B? Do I need to delete it twice ?

It depends on your policy. Don't read into the docs. They are literal. If you set unlink to ff then it unlinks first found. If it's set to the default all then it unlinks all. It's exactly what it says on the tin.

[trapexit]

The policy "newest" is for selecting which filesystem to write to, not which to read from, right?

functions have policies. the policy selects the file/s to act on. And no... as shown in the docs there is no read or write policy because you don't read and write to files but file descriptors. You must open or create a file first.

[X-Ryl669]

Ok, it's clearer. What happens if policy is all and I'm unlinking a file that's on both FS and one FS is read only? Will it report success (but the file will still be listed, as expected) or will it report failure and actually delete one of the files on the R/W FS? You can't revert a deletion I guess, so is there heuristics here?

[trapexit]

Please, It's all explained in the docs. https://trapexit.github.io/mergerfs/latest/config/functions_categories_policies/#filtering