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

[Ross Zwisler]

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: âdax_insert_mappingâ defined but not used [-Werror=unused-function]
> fs/dax.c:512:12: error: âcopy_user_daxâ defined but not used [-Werror=unused-function]
> fs/dax.c:490:12: error: âdax_load_holeâ defined but not used [-Werror=unused-function]
> fs/dax.c:294:14: error: âgrab_mapping_entryâ 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@xxxxxxxx>

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