On Wed, Oct 04, 2023 at 09:47:24AM +0100, John Garry wrote: > 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? Agreed - I was going to make that comment myself about using EINVAL instead of EIO... -Dave. -- Dave Chinner david@xxxxxxxxxxxxx
