O_SYNC

Posted May 21, 2019 23:03 UTC (Tue) by nix (subscriber, #2304)
In reply to: O_SYNC by rweikusat2
Parent article: DAX semantics

It's outstanding modifications to a certain open file, this referring to a per-process data structure referred to by a file descriptor

That's not actually true (though in practice it usually is). It's outstanding modifications to a certain open file, this referring to a file description (not descriptor). This is not a single-process entity but can be shared among processes, all of which can be writing to the file description simultaneously: all that data needs synchronous flushing if O_SYNC is on, and the other writing processes will all be blocked if they try to write to it while that write is ongoing.