Re: [PATCH 2/4] readv.2: Document RWF_ATOMIC flag

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On 03/10/2023 20:25, Bart Van Assche wrote:
On 9/29/23 02:37, John Garry wrote:
+.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
+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.

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?


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