On Wed, Oct 04, 2023 at 09:47:24AM +0100, John Garry wrote:

On 03/10/2023 20:25, Bart Van Assche wrote:

quoted

On 9/29/23 02:37, John Garry wrote:

quoted

+.BR RWF_ATOMIC " (since Linux 6.7)"
+Allows block-based filesystems to indicate that write operations
will be issued
+with torn-write protection. Torn-write protection means that for a
power or any
+other hardware failure, all or none of the data from the write will
be stored,
+but never a mix of old and new data. This flag is meaningful only for
+.BR pwritev2 (),
+and its effect applies only to the data range written by the system
call.
+The total write length must be power-of-2 and must be sized between
+stx_atomic_write_unit_min and stx_atomic_write_unit_max, both
inclusive. The
+write must be at a natural offset within the file with respect to
the total
+write length. Torn-write protection only works with
+.B O_DIRECT
+flag, i.e. buffered writes are not supported. To guarantee
consistency from
+the write between a file's in-core state with the storage device,

It seems wrong to me to start the first sentence with "Allows". Atomic
behavior should be mandatory if RWF_ATOMIC has been set.

Yes, I agree that this has been poorly worded. Flag RWF_ATOMIC does not
indicate anything. I will fix it.

quoted

Additionally, shouldn't it be documented what value will be stored in
errno if the atomic write has been rejected?

So I was treating all atomic writes errors which don't follow the "rules" as
low-level I/O errors, which is -EIO. However, yes, I can document this.
Further to that, based on description of an error for O_DIRECT, which is to
return -EINVAL for misaligned, I think that -EINVAL may be better for any
atomic write rule violations. OK?

Agreed - I was going to make that comment myself about using EINVAL
instead of EIO...

-Dave.
-- 
Dave Chinner
david@fromorbit.com