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

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Date:   Mon, 28 Nov 2016 14:24:00 -0700
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Theodore Ts'o <tytso@....edu>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        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 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