btrfs-progs: build: improve autodetection of zoned mode

The zoned support requires a header file and some structures for full
support. There are distros that have only part of that and the
autodetection at configure time does not handle that properly, assuming
the user requested the support.

Check if there was any of the --*able-zoned options and if not detect
the support level and fallback to no zoned eventually, not requiring
users to specify --disable-zoned as before.

Issue: #425
Signed-off-by: David Sterba <dsterba@suse.com>

configure.ac

@@ -282,10 +282,31 @@ AC_CHECK_HEADER(linux/blkzoned.h, [blkzoned_found=yes], [blkzoned_found=no])
 AC_CHECK_MEMBER([struct blk_zone.capacity], [blkzoned_capacity=yes], [blkzoned_capacity=no], [[#include <linux/blkzoned.h>]])
 AX_CHECK_DEFINE([linux/blkzoned.h], [BLKGETZONESZ], [blkzoned_getzonesz=yes], [blkzoned_getzonesz=no])
 AC_ARG_ENABLE([zoned],
-	      AS_HELP_STRING([--disable-zoned], [disable zoned block device support]),
-	      [], [enable_zoned=$blkzoned_found]
+	      AS_HELP_STRING([--disable-zoned], [disable zoned block device support (default: detect)]),
+	      [], [enable_zoned=$blkzoned_capacity]
 )
 
+# Autodetect zoned support
+AS_IF([test "x$enableval" = "x"], [
+       cansupportzoned=yes
+       if test "x$blkzoned_found" = xno; then
+	       cansupportzoned=no
+       fi
+       if test "x$blkzoned_capacity" = xno; then
+	       cansupportzoned=no
+       fi
+       if test "x$blkzoned_getzonesz" = xno; then
+	       cansupportzoned=no
+       fi
+       if test "x$cansupportzoned" = xno; then
+	       AC_MSG_NOTICE([insufficient support for zoned mode, cannot enable])
+	       enable_zoned=no
+       else
+	       enable_zoned=yes
+       fi
+])
+
+# Explicitly requested by --enable-zoned
 AS_IF([test "x$enable_zoned" = xyes], [
        if test "x$blkzoned_found" = xno; then
 	       AC_MSG_ERROR([Couldn't find linux/blkzoned.h])