[PATCH] mm/damon: Fix missing-prototype build warning for 'damon_pa_apply_scheme()'

[SeongJae Park]

Kernel test robot found[1] commit ccd554f15bb1 ("mm/damon/paddr: support
the pageout scheme") on the -mm tree[2], which is introduced by the
patch titled 'mm-damon-paddr-support-the-pageout-scheme.patch'[3]
introduces following build warning, and therefore the build fails if
'CONFIG_WERROR=y'.

    linux/mm/damon/paddr.c:216:5: error: no previous prototype for ‘damon_pa_apply_scheme’ [-Werror=missing-prototypes]
     int damon_pa_apply_scheme(struct damon_ctx *ctx, struct damon_target *t,
         ^~~~~~~~~~~~~~~~~~~~~
    cc1: all warnings being treated as errors
    linux/scripts/Makefile.build:277: recipe for target 'mm/damon/paddr.o' failed

This commit fixes the warning by adding the missed prototype in the
header file.

Note: Because the reported '.config' introduces warnings on not only
DAMON but also other subsystems, I tested for only DAMON by adding the
below compiler flag in mm/damon/Makefile.

    ccflags-$(CONFIG_DAMON_PADDR)  += -Werror -Wmissing-prototypes

[1] https://lore.kernel.org/lkml/202110250029.5rftt73s-lkp@xxxxxxxxx/
[2] https://github.com/hnaz/linux-mm/commit/ccd554f15bb1cd977d740c1ea8241ecf95108c94
[3] https://lore.kernel.org/mm-commits/20211019213137.91_rr1GrX%25akpm@xxxxxxxxxxxxxxxxxxxx/

Fixes: ccd554f15bb1 ("mm/damon/paddr: support the pageout scheme") in -mm tree
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
---
 include/linux/damon.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 715dadd21f7c..9a327bc787b5 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -357,6 +357,8 @@ void damon_va_set_primitives(struct damon_ctx *ctx);
 void damon_pa_prepare_access_checks(struct damon_ctx *ctx);
 unsigned int damon_pa_check_accesses(struct damon_ctx *ctx);
 bool damon_pa_target_valid(void *t);
+int damon_pa_apply_scheme(struct damon_ctx *context, struct damon_target *t,
+		struct damon_region *r, struct damos *scheme);
 void damon_pa_set_primitives(struct damon_ctx *ctx);
 
 #endif	/* CONFIG_DAMON_PADDR */
-- 
2.17.1