kconfig: do not write .config if the content is the same

[carl9170fw.git] / config / confdata.c

diff --git a/config/confdata.c b/config/confdata.c
index da98566ccc6a45e68f1be3b03e7383831a7eb1a0..da208c47fcb844e3101382fdf38dcc9f773d24b8 100644 (file)
--- a/config/confdata.c
+++ b/config/confdata.c
@@ -3,6 +3,7 @@
  * Copyright (C) 2002 Roman Zippel <zippel@linux-m68k.org>
  */
 
+#include <sys/mman.h>
 #include <sys/stat.h>
 #include <ctype.h>
 #include <errno.h>
@@ -36,6 +37,52 @@ static bool is_dir(const char *path)
        return S_ISDIR(st.st_mode);
 }
 
+/* return true if the given two files are the same, false otherwise */
+static bool is_same(const char *file1, const char *file2)
+{
+       int fd1, fd2;
+       struct stat st1, st2;
+       void *map1, *map2;
+       bool ret = false;
+
+       fd1 = open(file1, O_RDONLY);
+       if (fd1 < 0)
+               return ret;
+
+       fd2 = open(file2, O_RDONLY);
+       if (fd2 < 0)
+               goto close1;
+
+       ret = fstat(fd1, &st1);
+       if (ret)
+               goto close2;
+       ret = fstat(fd2, &st2);
+       if (ret)
+               goto close2;
+
+       if (st1.st_size != st2.st_size)
+               goto close2;
+
+       map1 = mmap(NULL, st1.st_size, PROT_READ, MAP_PRIVATE, fd1, 0);
+       if (map1 == MAP_FAILED)
+               goto close2;
+
+       map2 = mmap(NULL, st2.st_size, PROT_READ, MAP_PRIVATE, fd2, 0);
+       if (map2 == MAP_FAILED)
+               goto close2;
+
+       if (bcmp(map1, map2, st1.st_size))
+               goto close2;
+
+       ret = true;
+close2:
+       close(fd2);
+close1:
+       close(fd1);
+
+       return ret;
+}
+
 /*
  * Create the parent directory of the given path.
  *
@@ -934,6 +981,13 @@ next:
        fclose(out);
 
        if (*tmpname) {
+               if (is_same(name, tmpname)) {
+                       conf_message("No change to %s", name);
+                       unlink(tmpname);
+                       sym_set_change_count(0);
+                       return 0;
+               }
+
                snprintf(oldname, sizeof(oldname), "%s.old", name);
                rename(name, oldname);
                if (rename(tmpname, name))