Re: [PATCH] nvme: Fix nvme_setup_command metadata trace event for cdw10

[John Garry]

On 06/07/2022 17:44, Keith Busch wrote:
> On Wed, Jul 06, 2022 at 06:34:34PM +0200, Christoph Hellwig wrote:
> > On Wed, Jul 06, 2022 at 10:26:09AM -0600, Keith Busch wrote:
> > > On Wed, Jul 06, 2022 at 06:18:25PM +0200, Christoph Hellwig wrote:
> > > > On Wed, Jul 06, 2022 at 10:13:22AM -0600, Keith Busch wrote:
> > > > > Did you test what the trace looks like afte this? We're losing valuable trace
> > > > > data here. The field is supposed to get CDW's 10 - 15, so that's 24 bytes.

ok, I just thought it was a typo, but did not know why you were using an 
array macro.

> I
> > > > > don't know why it cares that the address of the field being read is only 4
> > > > > bytes; we want everything that comes after it too.
> > > >
> > > > Because accesses should not spawn boundaries of members in structs unless
> > > > copying the entire struct.  If we want to trace the various fields we
> > > > need to individually assign them.
> > > >
> > > > Anyway, I'm dropping this patch from nvme-5.19 for now to let the
> > > > discussion conclude.
> > >
> > > How about this instead?
> >
> > Maybe a better option would be to use struct_group().
>
> Good call, I'd never used that macro before. The result produces anonymous
> unions like I just proposed, so yes, I like that option.
> .

The warning hints at using struct_group() also ...

Anyway, Keith, do you want to write a new patch or shall I?

Thanks,
John