rwf-sync · shipping · also per-write file-integrity completion

RWF_SYNC

RWF_SYNC is a Linux per-write flag that requests synchronized file-integrity completion for the range written by pwritev2().

Documented since Linux 4.7, this is the per-call counterpart of O_SYNC, and does not change the synchronization mode stored in the open file description. Within the preadv2/pwritev2 pair, the flag affects writes, not reads; check the returned byte count for a short transfer. [1]

File-integrity completion includes associated file metadata as well as data. It does not require cache bypass or turn several writes into one failure-atomic transaction. [2]

Linux v6.12 combines per-call synchronization bits with inherited open-mode bits: flags=0 does not disable O_SYNC or O_DSYNC. This is source inspection, not a power-loss test. [3]

Relations

related

RWF_DSYNC, O_SYNC, fsync, Directory fsync, Short write, RWF_ATOMIC, Open file description

Advantages

• Requests file-integrity completion for a selected write without changing the open mode.

Limitations

• Does not provide torn-write protection or a multi-file transaction.
• Does not establish persistence of a new directory entry.
• Does not promise a smaller physical flush or lower latency.

Citations

1. Linux man-pages: readv(2), per-write flags and short transfers (accessed 2026-11-12)
2. Linux man-pages: open(2), synchronized I/O completion (accessed 2026-11-12)
3. Linux v6.12: init_sync_kiocb, iocb_flags, kiocb_set_rw_flags and generic_write_sync (accessed 2026-11-12)

Further reading

4. Hesela: Per-write flags add requirements; they do not downgrade the open mode (accessed 2026-11-12)
5. Linux man-pages: fsync(2), file and directory persistence (accessed 2026-11-12)

JSON: /data/terms/rwf-sync.json