build: improve detection of kernel version and error handling

Thanks to Arkadiusz Miskiewicz from PLD for reporting.

	make: *** kernelrelease: No such file or directory. Stop.
	Found kernel version "...0" in
	ERROR: That kernel version is not supported. Please see
	INSTALL for minimum configuration.

diff --git a/configure.ac b/configure.ac
index 775d73aeda139b8d2b705b31bb198bafb8b14f7b..2c7b37c0c80d9cbd7ecb31681950c84daa7728b0 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -46,6 +46,7 @@ if grep -q "CentOS release 5\." /etc/redhat-release 2>/dev/null ||
        # Well, just a warning. Maybe the admin updated the kernel.
        echo "WARNING: This distribution's shipped kernel is not supported.";
 fi;
+AC_MSG_CHECKING([kernel version that we will build against])
 krel="$(make -sC ${kbuilddir} kernelrelease)";
 krel="${krel%%-*}";
 kmajor="${krel%%.*}";
@@ -61,14 +62,20 @@ else
                kstable=0;
        fi;
 fi;
-echo "Found kernel version $kmajor.$kminor.$kmicro.$kstable in $kbuilddir";
-if test "$kmajor" -gt 2 -o "$kminor" -gt 6 -o "$kmicro" -gt 36; then
-       echo "WARNING: You are trying a newer kernel. Results may vary. :-)";
-elif test \( "$kmajor" -lt 2 -o "$kminor" -lt 6 -o "$kmicro" -lt 17 \) -o \
-    \( "$kmajor" -eq 2 -a "$kminor" -eq 6 -a "$kmicro" -eq 18 -a \
-    "$kstable" -lt 5 \); then
-       echo "ERROR: That kernel version is not supported. Please see INSTALL for minimum configuration.";
-       exit 1;
+if test -z "$kmajor" -o -z "$kminor" -o -z "$kmicro"; then
+       echo "WARNING: Version detection did not succeed. Continue at own luck.";
+else
+       echo "$kmajor.$kminor.$kmicro.$kstable in $kbuilddir";
+       if test "$kmajor" -gt 2 -o "$kminor" -gt 6 -o "$kmicro" -gt 36; then
+               echo "WARNING: You are trying a newer kernel. Results may vary. :-)";
+       elif test \( "$kmajor" -lt 2 -o \
+           \( "$kmajor" -eq 2 -a "$kminor" -lt 6 \) -o \
+           \( "$kmajor" -eq 2 -a "$kminor" -eq 0 -a "$kmicro" -lt 17 \) -o \
+           \( "$kmajor" -eq 2 -a "$kminor" -eq 6 -a "$kmicro" -eq 18 -a \
+           "$kstable" -lt 5 \) \); then
+               echo "ERROR: That kernel version is not supported. Please see INSTALL for minimum configuration.";
+               exit 1;
+       fi;
 fi;
 
 AC_SUBST([regular_CFLAGS])