[PATCH] erofs-utils: avoid PAGE_SIZE redefinition

[Gao Xiang]

Buildroot autobuild reported a PAGE_SIZE redefinition with some
configrations on i586 toolchain [1] (I didn't notice such report
from erofs-utils travis CI or distribution builds before.)

In file included from config.c:11:
../include/erofs/internal.h:27: error: "PAGE_SIZE" redefined [-Werror]
 #define PAGE_SIZE  (1U << PAGE_SHIFT)

In file included from ../include/erofs/defs.h:17,
                 from ../include/erofs/config.h:12,
                 from ../include/erofs/print.h:12,
                 from config.c:10:
.../sysroot/usr/include/limits.h:89: note: this is the location of the previous definition
 #define PAGE_SIZE PAGESIZE

cc1: all warnings being treated as errors

Fix it now.

[1] http://autobuild.buildroot.net/results/340b98caa45bafd43f109002be9da59ba7f6d971
Signed-off-by: Gao Xiang <hsiangkao at aol.com>
---
 include/erofs/internal.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/erofs/internal.h b/include/erofs/internal.h
index e7d5a64..41da189 100644
--- a/include/erofs/internal.h
+++ b/include/erofs/internal.h
@@ -23,8 +23,18 @@ typedef unsigned short umode_t;
 #define PATH_MAX        4096    /* # chars in a path name including nul */
 #endif
 
+#ifndef PAGE_SHIFT
 #define PAGE_SHIFT		(12)
+#endif
+
+#ifndef PAGE_SIZE
 #define PAGE_SIZE		(1U << PAGE_SHIFT)
+#endif
+
+/* no obvious reason to support explicit PAGE_SIZE != 4096 for now */
+#if PAGE_SIZE != 4096
+#error incompatible PAGE_SIZE is already defined
+#endif
 
 #define LOG_BLOCK_SIZE          (12)
 #define EROFS_BLKSIZ            (1U << LOG_BLOCK_SIZE)
-- 
2.20.1