streamline_config.pl: add LMC_KEEP to preserve some kconfigs

Sometimes it is useful to preserve batches of configs when making
localmodconfig. For example, I usually don't want any usb and fs
modules to be disabled. Now we can do it by:

 $ make LMC_KEEP="drivers/usb:fs" localmodconfig

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Documentation/admin-guide/README.rst

@@ -209,15 +209,22 @@ Configuring the kernel
                            store the lsmod of that machine into a file
                            and pass it in as a LSMOD parameter.
 
+                           Also, you can preserve modules in certain folders
+                           or kconfig files by specifying their paths in
+                           parameter LMC_KEEP.
+
                    target$ lsmod > /tmp/mylsmod
                    target$ scp /tmp/mylsmod host:/tmp
 
-                   host$ make LSMOD=/tmp/mylsmod localmodconfig
+                   host$ make LSMOD=/tmp/mylsmod \
+                           LMC_KEEP="drivers/usb:drivers/gpu:fs" \
+                           localmodconfig
 
                            The above also works when cross compiling.
 
      "make localyesconfig" Similar to localmodconfig, except it will convert
-                           all module options to built in (=y) options.
+                           all module options to built in (=y) options. You can
+                           also preserve modules by LMC_KEEP.
 
      "make kvmconfig"   Enable additional options for kvm guest kernel support.
 

scripts/kconfig/Makefile

@@ -123,7 +123,9 @@ help:
 	@echo  '  gconfig	  - Update current config utilising a GTK+ based front-end'
 	@echo  '  oldconfig	  - Update current config utilising a provided .config as base'
 	@echo  '  localmodconfig  - Update current config disabling modules not loaded'
+	@echo  '                    except those preserved by LMC_KEEP environment variable'
 	@echo  '  localyesconfig  - Update current config converting local mods to core'
+	@echo  '                    except those preserved by LMC_KEEP environment variable'
 	@echo  '  defconfig	  - New config with default from ARCH supplied defconfig'
 	@echo  '  savedefconfig   - Save current config as ./defconfig (minimal config)'
 	@echo  '  allnoconfig	  - New config where all options are answered with no'

scripts/kconfig/streamline_config.pl

@@ -143,6 +143,7 @@ sub read_config {
 my %selects;
 my %prompts;
 my %objects;
+my %config2kfile;
 my $var;
 my $iflevel = 0;
 my @ifdeps;
@@ -201,6 +202,7 @@ sub read_kconfig {
 	if (/^\s*(menu)?config\s+(\S+)\s*$/) {
 	    $state = "NEW";
 	    $config = $2;
+	    $config2kfile{"CONFIG_$config"} = $kconfig;
 
 	    # Add depends for 'if' nesting
 	    for (my $i = 0; $i < $iflevel; $i++) {
@@ -591,6 +593,20 @@ sub loop_select {
 }
 
 my %setconfigs;
+my @preserved_kconfigs = split(/:/,$ENV{LMC_KEEP});
+
+sub in_preserved_kconfigs {
+    my $kconfig = $config2kfile{$_[0]};
+    if (!defined($kconfig)) {
+        return 0;
+    }
+    foreach my $excl (@preserved_kconfigs) {
+        if($kconfig =~ /^$excl/) {
+            return 1;
+        }
+    }
+    return 0;
+}
 
 # Finally, read the .config file and turn off any module enabled that
 # we could not find a reason to keep enabled.
@@ -644,6 +660,11 @@ sub loop_select {
     }
 
     if (/^(CONFIG.*)=(m|y)/) {
+        if (in_preserved_kconfigs($1)) {
+            dprint "Preserve config $1";
+            print;
+            next;
+        }
 	if (defined($configs{$1})) {
 	    if ($localyesconfig) {
 	        $setconfigs{$1} = 'y';