[PATCH] erofs-utils: mkfs: Use extended inodes when ctime is set

[David Anderson]

On Mon, Feb 28, 2022 at 10:14 PM Gao Xiang <hsiangkao at linux.alibaba.com> wrote:
>
>
> (Or maybe just "--preserve-mtime" if it's supposed to be used frequently in
>  specific use cases...)

Looking at this again - is a new flag needed?

If -T is specified, the build will be reproducible. All timestamps
will be equal, and we'll never force an extended inode due to
mismatching timestamps. The patch has no effect in this case.

If -T is *not* specified, inode mtime *could* be reproducible
(depending on how the user creates the files), but sbi.build_time
isn't. Any of these inodes that gets the compact layout will use the
unreproducible build time instead. So, switching to extended inodes
here strictly improves reproducibility and determinism.

That said, it is a change in behavior, so maybe that warrants a flag anyway.

For what it's worth, in AOSP, "-T" is specified for production builds.
Non-production builds have "mtime" preserved for pushing incremental
changes.

Best,

-David