Re: [PATCH] [RFC] iomap: Use FUA for pure data O_DSYNC DIO writes

[Christoph Hellwig <hch@lst.de>]

On Fri, Mar 02, 2018 at 11:20:31PM +0100, Christoph Hellwig wrote:
> > --- a/fs/xfs/xfs_file.c
> > +++ b/fs/xfs/xfs_file.c
> > @@ -732,6 +732,11 @@ xfs_file_write_iter(
> >  		ret = xfs_file_dio_aio_write(iocb, from);
> >  		if (ret == -EREMCHG)
> >  			goto buffered;
> > +		/*
> > +		 * Direct IO handles sync type writes internally on I/O
> > +		 * completion.
> > +		 */
> > +		return ret;
> >  	} else {
> >  buffered:
> >  		ret = xfs_file_buffered_aio_write(iocb, from);
> 
> The else is not needed and you can now have a much more sensible
> code flow here:
> 
> 		ret = xfs_file_dio_aio_write(iocb, from);
> 		if (ret != -EREMCHG))
> 			return ret;
> 	}
> 
> 	ret = xfs_file_buffered_aio_write(iocb, from);

Actually a little more complicated due to the DAX case, and the fact
that both your original and this new version miss the XFS_STATS_ADD
call.  But you get the idea.  While we're at it we should probably
also skil the generic_write_sync call for DAX pure overwrites while
we're at it.