As you noted, Apple's fsync() behavior is defensible if PLP is assumed. Committing through the PLP cache isn't how these drives are meant to operate - hence the poor behavior of F_FULLSYNC.

But this isn't specific to Macs and iDevices. Some non-PLP drives also struggle with sync writes on FreeBSD [1]. Most enterprises running RDBMS mandate PLP for both performance and reliability. I understand why this is frustrating for porting Linux, but Apple is allowed to make strong assumptions about how their hardware interoperates.

[1] https://www.truenas.com/community/threads/slog-and-power-los...