[PATCH] erofs-utils: support detecting maximum block size

[Gao Xiang]

Previously PAGE_SIZE was actually unset for most cases so that it was
always hard-coded 4096.

In order to set EROFS_MAX_BLOCK_SIZE correctly, let's detect the real
page size when configuring.

Cc: Kelvin Zhang <zhangkelvin at google.com>
Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
---
 configure.ac             | 38 ++++++++++++++++++++++++++++++++++++++
 include/erofs/internal.h |  8 +++-----
 lib/namei.c              |  2 +-
 mkfs/main.c              |  4 ++--
 4 files changed, 44 insertions(+), 8 deletions(-)

diff --git a/configure.ac b/configure.ac
index 4dbe86f..2ade490 100644
--- a/configure.ac
+++ b/configure.ac
@@ -59,6 +59,8 @@ AC_DEFUN([EROFS_UTILS_PARSE_DIRECTORY],
  fi
 ])
 
+AC_ARG_VAR([MAX_BLOCK_SIZE], [The maximum block size which erofs-utils supports])
+
 AC_ARG_ENABLE([debug],
     [AS_HELP_STRING([--enable-debug],
                     [enable debugging mode @<:@default=no@:>@])],
@@ -202,6 +204,35 @@ AC_CHECK_FUNCS(m4_flatten([
 	tmpfile64
 	utimensat]))
 
+# Detect maximum block size if necessary
+AS_IF([test "x$MAX_BLOCK_SIZE" = "x"], [
+  AC_CACHE_CHECK([sysconf (_SC_PAGESIZE)], [erofs_cv_max_block_size],
+               AC_RUN_IFELSE([AC_LANG_PROGRAM(
+[[
+#include <unistd.h>
+#include <stdio.h>
+]],
+[[
+    int result;
+    FILE *f;
+
+    result = sysconf(_SC_PAGESIZE);
+    if (result < 0)
+	return 1;
+
+    f = fopen("conftest.out", "w");
+    if (!f)
+	return 1;
+
+    fprintf(f, "%d", result);
+    fclose(f);
+    return 0;
+]])],
+                             [erofs_cv_max_block_size=`cat conftest.out`],
+                             [],
+                             []))
+], [erofs_cv_max_block_size=$MAX_BLOCK_SIZE])
+
 # Configure debug mode
 AS_IF([test "x$enable_debug" != "xno"], [], [
   dnl Turn off all assert checking.
@@ -367,6 +398,13 @@ if test "x${have_liblzma}" = "xyes"; then
   AC_SUBST([liblzma_CFLAGS])
 fi
 
+# Dump maximum block size
+AS_IF([test "x$erofs_cv_max_block_size" = "x"],
+      [$erofs_cv_max_block_size = 4096], [])
+
+AC_DEFINE_UNQUOTED([EROFS_MAX_BLOCK_SIZE], [$erofs_cv_max_block_size],
+		   [The maximum block size which erofs-utils supports])
+
 AC_CONFIG_FILES([Makefile
 		 man/Makefile
 		 lib/Makefile
diff --git a/include/erofs/internal.h b/include/erofs/internal.h
index b3d04be..ee301e0 100644
--- a/include/erofs/internal.h
+++ b/include/erofs/internal.h
@@ -27,15 +27,13 @@ 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)
+#define PAGE_SIZE		4096
 #endif
 
+#ifndef EROFS_MAX_BLOCK_SIZE
 #define EROFS_MAX_BLOCK_SIZE	PAGE_SIZE
+#endif
 
 #define EROFS_ISLOTBITS		5
 #define EROFS_SLOTSIZE		(1U << EROFS_ISLOTBITS)
diff --git a/lib/namei.c b/lib/namei.c
index 3d0cf93..3751741 100644
--- a/lib/namei.c
+++ b/lib/namei.c
@@ -137,7 +137,7 @@ int erofs_read_inode_from_disk(struct erofs_inode *vi)
 		vi->u.chunkbits = sbi.blkszbits +
 			(vi->u.chunkformat & EROFS_CHUNK_FORMAT_BLKBITS_MASK);
 	} else if (erofs_inode_is_data_compressed(vi->datalayout)) {
-		if (erofs_blksiz() != PAGE_SIZE)
+		if (erofs_blksiz() != EROFS_MAX_BLOCK_SIZE)
 			return -EOPNOTSUPP;
 		return z_erofs_fill_inode(vi);
 	}
diff --git a/mkfs/main.c b/mkfs/main.c
index 3ec4903..a6a2d0e 100644
--- a/mkfs/main.c
+++ b/mkfs/main.c
@@ -532,7 +532,7 @@ static int mkfs_parse_options_cfg(int argc, char *argv[])
 		cfg.c_dbg_lvl = EROFS_ERR;
 		cfg.c_showprogress = false;
 	}
-	if (cfg.c_compr_alg[0] && erofs_blksiz() != PAGE_SIZE) {
+	if (cfg.c_compr_alg[0] && erofs_blksiz() != EROFS_MAX_BLOCK_SIZE) {
 		erofs_err("compression is unsupported for now with block size %u",
 			  erofs_blksiz());
 		return -EINVAL;
@@ -670,7 +670,7 @@ static void erofs_mkfs_default_options(void)
 {
 	cfg.c_showprogress = true;
 	cfg.c_legacy_compress = false;
-	sbi.blkszbits = ilog2(PAGE_SIZE);
+	sbi.blkszbits = ilog2(EROFS_MAX_BLOCK_SIZE);
 	sbi.feature_incompat = EROFS_FEATURE_INCOMPAT_LZ4_0PADDING;
 	sbi.feature_compat = EROFS_FEATURE_COMPAT_SB_CHKSUM |
 			     EROFS_FEATURE_COMPAT_MTIME;
-- 
2.24.4