rwf-noappend · shipping · also per-write append override

RWF_NOAPPEND

RWF_NOAPPEND is a Linux pwritev2 flag that suppresses O_APPEND placement for one write operation.

Documented since Linux 6.9, it overrides append placement for the call, not the shared file-status flag. A nonnegative offset selects the position; offset -1 still uses and updates the shared current offset. [1] [2] [3]

In v6.17, kiocb_set_rw_flags returns EPERM when suppressing append would violate an append-only inode, and EINVAL for simultaneous append/noappend flags. It is not a bypass of append-only inode protection. [2]

A zero-total-length write can finish before flag validation. EOPNOTSUPP can mean an unsupported flag or write path, not only an old kernel. Test a nonempty disposable-file operation and inspect placement and errors. [3]

Relations

related

RWF_APPEND, O_APPEND, pwrite, File offset, Open file description, Short write, writev, fsync

Advantages

• Keeps per-call positioning separate from later writes through the same open file description.

Limitations

• Availability must be checked for the actual kernel and target, not inferred from a successful empty write. [3]
• Does not replace synchronization, short-write handling or protection against overlapping writers. [1]

Citations

1. Linux man-pages: readv(2), pwritev2 per-call flags and offset semantics (accessed 2026-11-11)
2. Linux v6.17: kiocb_set_rw_flags validation and per-operation append state (accessed 2026-11-11)
3. Linux v6.17: pwritev2 dispatch, current offsets and zero-length write handling (accessed 2026-11-11)

Further reading

4. Hesela: Atomic rename is not a durable commit, per-write positioning (accessed 2026-11-11)

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