[PATCHv6 11/11] iomap: add support for dma aligned direct-io

[Eric Farman]

On Tue, 2022-06-28 at 21:52 -0600, Keith Busch wrote:
> On Tue, Jun 28, 2022 at 11:18:34PM -0400, Eric Farman wrote:
> > Sort of. In the working case, I see a set of iovecs come through
> > with
> > different counts:
> > 
> > base	count
> > 0000	0001
> > 0000	0200
> > 0000	0400
> > 0000	0800
> > 0000	1000
> > 0001	1000
> > 0200	1000 << Change occurs here
> > 0400	1000
> > 0800	1000
> > 1000	1000
> > 
> > EINVAL was being returned for any of these iovecs except the page-
> > aligned ones. Once the x200 request returns 0, the remainder of the
> > above list was skipped and the requests continue elsewhere on the
> > file.
> > 
> > Still not sure how our request is getting us into this process.
> > We're
> > simply asking to read a single block, but that's somewhere within
> > an
> > image file.
> 
> I thought this was sounding like some kind of corruption. I tested
> ext4 on
> various qemu devices with 4k logical block sizes, and it all looks
> okay there.
> 
> What block driver are you observing this with?

s390 dasd

This made me think to change my rootfs, and of course the problem goes
away once on something like a SCSI volume.

So crawling through the dasd (instead of virtio) driver and I finally
find the point where a change to dma_alignment (which you mentioned
earlier) would actually fit.

Such a change fixes this for me, so I'll run it by our DASD guys.
Thanks for your help and patience.

Eric