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

[John Garry]

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
> > +.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.

> 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?

Thanks,
John