linux-kernel - Re: [PATCH] dax: try to avoid unused function warnings

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Message-ID: <20170110194408.GA14287@linux.intel.com>
Date:   Tue, 10 Jan 2017 12:44:08 -0700
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Theodore Ts'o <tytso@....edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...ux.intel.com>,
        Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Chinner <dchinner@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dax: try to avoid unused function warnings

On Tue, Jan 10, 2017 at 05:15:57PM +0100, Arnd Bergmann wrote:
> On Monday, November 28, 2016 2:24:00 PM CET Ross Zwisler wrote:
> > On Mon, Nov 28, 2016 at 10:12:17PM +0100, Arnd Bergmann wrote:
> > > Without the get_block based I/O, we get warnings when CONFIG_FS_IOMAP
> > > is disabled:
> > > 
> > > fs/dax.c:736:12: error: ‘dax_insert_mapping’ defined but not used [-Werror=unused-function]
> > > fs/dax.c:512:12: error: ‘copy_user_dax’ defined but not used [-Werror=unused-function]
> > > fs/dax.c:490:12: error: ‘dax_load_hole’ defined but not used [-Werror=unused-function]
> > > fs/dax.c:294:14: error: ‘grab_mapping_entry’ defined but not used [-Werror=unused-function]
> > > 
> > > This patch blindly marks those as __maybe_unused, which avoids the warnings.
> > > However, I suspect that there is actually more code in this file that should
> > > not be provided without CONFIG_FS_IOMAP even though we don't get a warning
> > > for it, and that we actually want a different rework, so please treat this
> > > as a bug report. I have applied the patch locally in my randconfig build
> > > setup to avoid seeing the warnings.
> > > 
> > > Fixes: 5ac65736f740 ("dax: rip out get_block based IO support")
> > > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > 
> > Thanks for the report.  I think the right way to deal with this is to just
> > select FS_IOMAP when we pull in the DAX code.  I sent out a patch last week
> > that does this:
> > 
> > https://lkml.org/lkml/2016/11/23/591
> 
> It seems we never got agreement on the approach, and we still get the
> warnings above in v4.10. Should we use my patch to fix up 4.10 and get
> a clean build again? It no longer applies, but I have a rebased version
> that I can send.
> 
> 	Arnd

Thanks for the reminder, this one slipped through the cracks.  I still think
the right way to go with this is to fix up DAX's dependence on FS_IOMAP.  I'll
send out an updated patch.