Re: [PATCH] iomap: enforce DIO alignment check in iomap]

[Keith Busch <kbusch@kernel.org>]

On Wed, Jun 10, 2026 at 06:58:13PM +0200, Carlos Maiolino wrote:
> On Wed, Jun 10, 2026 at 09:37:17AM -0600, Keith Busch wrote:
> > On Wed, Jun 10, 2026 at 05:27:42PM +0200, Carlos Maiolino wrote:
> > > The DIO alignment check has been lifted from iomap layer to rely on the
> > > block layer to enforce proper alignment when issuing direct IO
> > > operations. This though, depending on the IO size and buffer address
> > > passed to the IO operation may lead to user-visible behavior change.
> > > 
> > > This has been caught initially by LTP test diotest4 running on
> > > PPC architecture, where the test fails because a read() operation
> > > with a supposedly misaligned buffer succeeds instead of an expected
> > > -EINVAL.
> > 
> > It's not supposed to matter where in the stack we determined this be an
> > invalid request: it should still fail if it's misaligned. Could you
> > clarify how this is succeeding?
> 
> Fair enough, can you point me to where the alignment is supposed to be
> checked? 

https://elixir.bootlin.com/linux/v7.1-rc7/source/block/blk-merge.c#L352

It does require that someone calls the bio split-to-limits routine,
which I had taken for granted as a given, but I realize that some
drivers don't do that. What block device are you using for your test?