kconfig: allow specifying the seed for randconfig

For reproducibility, it can be useful to be able to specify the
seed to use to seed the RNG.

Add a new KCONFIG_SEED environment variable which can be set to
the seed to use:
    $ make KCONFIG_SEED=42 randconfig
    $ sha1sum .config
    70a128c8dcc61303069e1be352cce64114dfcbca  .config
    $ make KCONFIG_SEED=42 randconfig
    $ sha1sum .config
    70a128c8dcc61303069e1be352cce64114dfcbca  .config

It's very usefull for eg. debugging the kconfig parser.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

2 files changed, 20 insertions, 1 deletions

diff --git a/Documentation/kbuild/kconfig.txt b/Documentation/kbuild/kconfig.txt
index b8b77bbc784f..dbf746b70553 100644
--- a/Documentation/kbuild/kconfig.txt
+++ b/Documentation/kbuild/kconfig.txt
@@ -90,6 +90,15 @@ disable the options that are explicitly listed in the specified
 mini-config files.
 
 ______________________________________________________________________
+Environment variables for 'randconfig'
+
+KCONFIG_SEED
+--------------------------------------------------
+You can set this to the integer value used to seed the RNG, if you want
+to somehow debug the behaviour of the kconfig parser/frontends.
+If not set, the current time will be used.
+
+______________________________________________________________________
 Environment variables for 'silentoldconfig'
 
 KCONFIG_NOSILENTUPDATE
diff --git a/scripts/kconfig/conf.c b/scripts/kconfig/conf.c
index e39fcd8143ea..bde5b95c8c19 100644
--- a/scripts/kconfig/conf.c
+++ b/scripts/kconfig/conf.c
@@ -13,6 +13,7 @@
 #include <getopt.h>
 #include <sys/stat.h>
 #include <sys/time.h>
+#include <errno.h>
 
 #include "lkc.h"
 
@@ -514,14 +515,23 @@ int main(int ac, char **av)
                 {
                         struct timeval now;
                         unsigned int seed;
+                        char *seed_env;
 
                         /*
                          * Use microseconds derived seed,
                          * compensate for systems where it may be zero
                          */
                         gettimeofday(&now, NULL);
-
                         seed = (unsigned int)((now.tv_sec + 1) * (now.tv_usec + 1));
+
+                        seed_env = getenv("KCONFIG_SEED");
+                        if( seed_env && *seed_env ) {
+                                char *endp;
+                                int tmp = (int)strtol(seed_env, &endp, 10);
+                                if (*endp == '\0') {
+                                        seed = tmp;
+                                }
+                        }
                         srand(seed);
                         break;
                 }