Re: [PATCH v6 00/10] block atomic writes

[John Garry]

On 05/04/2024 11:20, Kent Overstreet wrote:
> > > The thing is that there's no requirement for an interface as complex as
> > > the one you're proposing here.  I've talked to a few database people
> > > and all they want is to increase the untorn write boundary from "one
> > > disc block" to one database block, typically 8kB or 16kB.
> > >
> > > So they would be quite happy with a much simpler interface where they
> > > set the inode block size at inode creation time, and then all writes to
> > > that inode were guaranteed to be untorn.  This would also be simpler to
> > > implement for buffered writes.
> > You're conflating filesystem functionality that applications will use
> > with hardware and block-layer enablement that filesystems and
> > filesystem utilities need to configure the filesystem in ways that
> > allow users to make use of atomic write capability of the hardware.
> >
> > The block layer functionality needs to export everything that the
> > hardware can do and filesystems will make use of. The actual
> > application usage and setup of atomic writes at the filesystem/page
> > cache layer is a separate problem.  i.e. The block layer interfaces
> > need only support direct IO and expose limits for issuing atomic
> > direct IO, and nothing more. All the more complex stuff to make it
> > "easy to use" is filesystem level functionality and completely
> > outside the scope of this patchset....
> A CoW filesystem can implement atomic writes without any block device
> support. It seems to me that might have been the easier place to start -
> start by getting the APIs right, then do all the plumbing for efficient
> untorn writes on non CoW filesystems...

03/10 and 04/10 in this series define the user API, i.e. RWF_ATOMIC and 
statx updates.

Any filesystem-specific changes - like in 
https://lore.kernel.org/linux-xfs/20240304130428.13026-1-john.g.garry@xxxxxxxxxx/ 
- are just for enabling this API for that filesystem.