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From: David Howells <dhowells@redhat.com>
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References: <ZGcu6GVxOgYfy8x9@infradead.org> <20230519074047.1739879-1-dhowells@redhat.com> <20230519074047.1739879-6-dhowells@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH v20 05/32] splice: Make splice from a DAX file use direct_splice_read()
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Date: Fri, 19 May 2023 09:48:47 +0100
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Christoph Hellwig <hch@infradead.org> wrote:

> On Fri, May 19, 2023 at 08:40:20AM +0100, David Howells wrote:
> > +#ifdef CONFIG_FS_DAX
> > +	if (IS_DAX(in->f_mapping->host))
> 
> No need for the ifdef.  IS_DAX is compile-time false if CONFIG_FS_DAX
> is not set.

Ah - it's not that IS_DAX() is conditionalised, it's that S_DAX is.  There's a
bunch of places that use CONFIG_FS_DAX blocks, but I guess that's because they
include calls to functions that are conditionalised out.

I wonder if the dax_iomap_rw() declaration in the header can have a non-DAX
fallback that returns an error and then we can get rid of some of the other
conditionalisation.

David