nilfs2: do not use unexported cpu_to_le32()/le32_to_cpu() in uapi header

cpu_to_le32/le32_to_cpu is defined in include/linux/byteorder/generic.h,
which is not exported to user-space.

UAPI headers must use the ones prefixed with double-underscore.

Detected by compile-testing exported headers:

  include/linux/nilfs2_ondisk.h: In function `nilfs_checkpoint_set_snapshot':
  include/linux/nilfs2_ondisk.h:536:17: error: implicit declaration of function `cpu_to_le32' [-Werror=implicit-function-declaration]
    cp->cp_flags = cpu_to_le32(le32_to_cpu(cp->cp_flags) |  \
                   ^
  include/linux/nilfs2_ondisk.h:552:1: note: in expansion of macro `NILFS_CHECKPOINT_FNS'
   NILFS_CHECKPOINT_FNS(SNAPSHOT, snapshot)
   ^~~~~~~~~~~~~~~~~~~~
  include/linux/nilfs2_ondisk.h:536:29: error: implicit declaration of function `le32_to_cpu' [-Werror=implicit-function-declaration]
    cp->cp_flags = cpu_to_le32(le32_to_cpu(cp->cp_flags) |  \
                               ^
  include/linux/nilfs2_ondisk.h:552:1: note: in expansion of macro `NILFS_CHECKPOINT_FNS'
   NILFS_CHECKPOINT_FNS(SNAPSHOT, snapshot)
   ^~~~~~~~~~~~~~~~~~~~
  include/linux/nilfs2_ondisk.h: In function `nilfs_segment_usage_set_clean':
  include/linux/nilfs2_ondisk.h:622:19: error: implicit declaration of function `cpu_to_le64' [-Werror=implicit-function-declaration]
    su->su_lastmod = cpu_to_le64(0);
                     ^~~~~~~~~~~

Link: http://lkml.kernel.org/r/20190605053006.14332-1-yamada.masahiro@socionext.com
Fixes: e63e88bc ("nilfs2: move ioctl interface and disk layout to uapi separately")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Joe Perches <joe@perches.com>
Cc: <stable@vger.kernel.org>	[4.9+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/uapi/linux/nilfs2_ondisk.h

@@ -29,7 +29,7 @@
 
 #include <linux/types.h>
 #include <linux/magic.h>
-
+#include <asm/byteorder.h>
 
 #define NILFS_INODE_BMAP_SIZE	7
 
@@ -533,19 +533,19 @@ enum {
 static inline void							\
 nilfs_checkpoint_set_##name(struct nilfs_checkpoint *cp)		\
 {									\
-	cp->cp_flags = cpu_to_le32(le32_to_cpu(cp->cp_flags) |		\
-				   (1UL << NILFS_CHECKPOINT_##flag));	\
+	cp->cp_flags = __cpu_to_le32(__le32_to_cpu(cp->cp_flags) |	\
+				     (1UL << NILFS_CHECKPOINT_##flag));	\
 }									\
 static inline void							\
 nilfs_checkpoint_clear_##name(struct nilfs_checkpoint *cp)		\
 {									\
-	cp->cp_flags = cpu_to_le32(le32_to_cpu(cp->cp_flags) &		\
+	cp->cp_flags = __cpu_to_le32(__le32_to_cpu(cp->cp_flags) &	\
 				   ~(1UL << NILFS_CHECKPOINT_##flag));	\
 }									\
 static inline int							\
 nilfs_checkpoint_##name(const struct nilfs_checkpoint *cp)		\
 {									\
-	return !!(le32_to_cpu(cp->cp_flags) &				\
+	return !!(__le32_to_cpu(cp->cp_flags) &				\
 		  (1UL << NILFS_CHECKPOINT_##flag));			\
 }
 
@@ -595,20 +595,20 @@ enum {
 static inline void							\
 nilfs_segment_usage_set_##name(struct nilfs_segment_usage *su)		\
 {									\
-	su->su_flags = cpu_to_le32(le32_to_cpu(su->su_flags) |		\
+	su->su_flags = __cpu_to_le32(__le32_to_cpu(su->su_flags) |	\
 				   (1UL << NILFS_SEGMENT_USAGE_##flag));\
 }									\
 static inline void							\
 nilfs_segment_usage_clear_##name(struct nilfs_segment_usage *su)	\
 {									\
 	su->su_flags =							\
-		cpu_to_le32(le32_to_cpu(su->su_flags) &			\
+		__cpu_to_le32(__le32_to_cpu(su->su_flags) &		\
 			    ~(1UL << NILFS_SEGMENT_USAGE_##flag));      \
 }									\
 static inline int							\
 nilfs_segment_usage_##name(const struct nilfs_segment_usage *su)	\
 {									\
-	return !!(le32_to_cpu(su->su_flags) &				\
+	return !!(__le32_to_cpu(su->su_flags) &				\
 		  (1UL << NILFS_SEGMENT_USAGE_##flag));			\
 }
 
@@ -619,15 +619,15 @@ NILFS_SEGMENT_USAGE_FNS(ERROR, error)
 static inline void
 nilfs_segment_usage_set_clean(struct nilfs_segment_usage *su)
 {
-	su->su_lastmod = cpu_to_le64(0);
-	su->su_nblocks = cpu_to_le32(0);
-	su->su_flags = cpu_to_le32(0);
+	su->su_lastmod = __cpu_to_le64(0);
+	su->su_nblocks = __cpu_to_le32(0);
+	su->su_flags = __cpu_to_le32(0);
 }
 
 static inline int
 nilfs_segment_usage_clean(const struct nilfs_segment_usage *su)
 {
-	return !le32_to_cpu(su->su_flags);
+	return !__le32_to_cpu(su->su_flags);
 }
 
 /**