[PATCH v7 0/3] FDP and per-io hints

[Keith Busch]

On Fri, Oct 11, 2024 at 02:21:02PM +0200, Javier Gonzalez wrote:
> > That's a lot of marketing babble :)    What exact thing is missing
> > from the passthrough interface when using say spdx over io_uring?
> 
> The block layer provides a lot of functionality that passthru cannot
> provide. A simple example would be splits. You know this :)
> 
> I am sure Jens and Keith can give you more specifics on their particular
> reasons.

Splitting, merging, cgroups, iostats, error retries, failover.

We have a recent change staged in 6.13 to try to count iostats on
passthrough, but it doesn't do discards.

Passthrough to partitions requires root access and the slow CAP_SYSADMIN
check on every IO.

Page cache. Though that may not readily work with this io_uring proposal
as-is either.

The generic IO path is safe to changing formats; passthrough isn't.

And it's just generally more work to port existing applications to use
the passthrough interface. It causes duplicating solutions to scenarios
the kernel already handles.