[jlokier]

> Byte range is support is interesting but also present in the Linux sync API: https://man7.org/linux/man-pages/man2/sync_file_range.2.html

Unfortunately, I think sync_file_range() provides much weaker guarantees than byte-range fsync() and even byte-range fdatasync().

As I understand it from historical behaviour and documentation, sync_file_range() doesn't push durability barriers down the underlying storage devices, nor does it ensure that all metadata needed to access the written pages is itself written and made durable, for example when writing to a hole in a sparse file, to the end-hole created by enlarging a file with ftruncate(), or to fallocate'd pages.

As a result, that means sync_file_range() can only be used as a performance tweak, and not for any durability guarantees that fdatasync() / fsync() are used for.

I'd be delighted to find this has improved since I last looked, but that's what I recall about sync_file_range().