Re: [PATCH 1/1] xfs: introduce new file range commit ioctls

Jeff Layton
2024-08-23T13:20:17Z

On Thu, 2024-08-22 at 21:12 -0700, Christoph Hellwig wrote:
> On Thu, Aug 22, 2024 at 05:01:22PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> >
> > This patch introduces two more new ioctls to manage atomic updates to
> > file contents -- XFS_IOC_START_COMMIT and XFS_IOC_COMMIT_RANGE. The
> > commit mechanism here is exactly the same as what XFS_IOC_EXCHANGE_RANGE
> > does, but with the additional requirement that file2 cannot have changed
> > since some sampling point. The start-commit ioctl performs the sampling
> > of file attributes.
>
> The code itself looks simply enough now, but how do we guarantee
> that ctime actually works as a full change count and not just by
> chance here?
>

With current mainline kernels it won't, but the updated multigrain
timestamp series is in linux-next and is slated to go into v6.12. At
that point it should be fine for this purpose.

--
Jeff Layton <jlayton@kernel.org>