[RFC][PATCH] kconfig: introduce listunknownconfig

[Sergey Senozhatsky <senozhatsky@chromium.org>]

The listunknownconfig option reads old .config and lists
all unrecognized symbols. This is especially useful for
continuous kernel uprevs when some symbols can be either
removed or renamed between kernel releases (which can go
unnoticed otherwise).

A recent real-life example of such a symbol rename
that quietly disabled some drivers after kernel uprev
is MFD_RK808 rename.

Example:
Suppose old .config has the following two options which
were removed from the recent kernel:

$ cat .config
CONFIG_DISABLE_BUGS=y

Running `make listunknownconfig` produces the following
list of unrecognized symbols:

.config:6:warning: unknown symbol: DISABLE_BUGS
.config:7:warning: unknown unset symbol: ENABLE_WINAPI

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 Documentation/kbuild/kconfig.rst |  8 +++++
 scripts/kconfig/Makefile         |  4 ++-
 scripts/kconfig/conf.c           |  8 +++++
 scripts/kconfig/confdata.c       | 55 ++++++++++++++++++++++++++++++++
 scripts/kconfig/lkc_proto.h      |  1 +
 5 files changed, 75 insertions(+), 1 deletion(-)

diff --git a/Documentation/kbuild/kconfig.rst b/Documentation/kbuild/kconfig.rst
index 6530ecd99da3..445c438dc741 100644
--- a/Documentation/kbuild/kconfig.rst
+++ b/Documentation/kbuild/kconfig.rst
@@ -29,6 +29,14 @@ To see a list of new config symbols, use::
 
 and the config program will list any new symbols, one per line.
 
+To see a list of config symbols that are not recognized anymore (e.g.
+removed or renamed), use::
+
+	cp user/some/old.config .config
+	make listunknownconfig
+
+and the config program will list any unrecognized symbols, one per line.
+
 Alternatively, you can use the brute force method::
 
 	make oldconfig
diff --git a/scripts/kconfig/Makefile b/scripts/kconfig/Makefile
index af1c96198f49..942316ddebd9 100644
--- a/scripts/kconfig/Makefile
+++ b/scripts/kconfig/Makefile
@@ -69,7 +69,8 @@ localyesconfig localmodconfig: $(obj)/conf
 #  deprecated for external use
 simple-targets := oldconfig allnoconfig allyesconfig allmodconfig \
 	alldefconfig randconfig listnewconfig olddefconfig syncconfig \
-	helpnewconfig yes2modconfig mod2yesconfig mod2noconfig
+	helpnewconfig yes2modconfig mod2yesconfig mod2noconfig \
+	listunknownconfig
 
 PHONY += $(simple-targets)
 
@@ -141,6 +142,7 @@ help:
 	@echo  '                    default value without prompting'
 	@echo  '  tinyconfig	  - Configure the tiniest possible kernel'
 	@echo  '  testconfig	  - Run Kconfig unit tests (requires python3 and pytest)'
+	@echo  '  listunknownconfig	- List unrecognized options'
 
 # ===========================================================================
 # object files used by all kconfig flavours
diff --git a/scripts/kconfig/conf.c b/scripts/kconfig/conf.c
index 33d19e419908..e26aa491be00 100644
--- a/scripts/kconfig/conf.c
+++ b/scripts/kconfig/conf.c
@@ -36,6 +36,7 @@ enum input_mode {
 	yes2modconfig,
 	mod2yesconfig,
 	mod2noconfig,
+	listunknownconfig,
 };
 static enum input_mode input_mode = oldaskconfig;
 static int input_mode_opt;
@@ -683,6 +684,7 @@ static const struct option long_opts[] = {
 	{"yes2modconfig", no_argument,       &input_mode_opt, yes2modconfig},
 	{"mod2yesconfig", no_argument,       &input_mode_opt, mod2yesconfig},
 	{"mod2noconfig",  no_argument,       &input_mode_opt, mod2noconfig},
+	{"listunknownconfig", no_argument,   &input_mode_opt, listunknownconfig},
 	{NULL, 0, NULL, 0}
 };
 
@@ -712,6 +714,7 @@ static void conf_usage(const char *progname)
 	printf("  --yes2modconfig         Change answers from yes to mod if possible\n");
 	printf("  --mod2yesconfig         Change answers from mod to yes if possible\n");
 	printf("  --mod2noconfig          Change answers from mod to no if possible\n");
+	printf("  --listunknownconfig     List config options that do not exist anymore\n");
 	printf("  (If none of the above is given, --oldaskconfig is the default)\n");
 }
 
@@ -823,6 +826,11 @@ int main(int ac, char **av)
 			exit(1);
 		}
 		break;
+	case listunknownconfig:
+		if (conf_read_list_unknown())
+			exit(1);
+		exit(0);
+		break;
 	default:
 		break;
 	}
diff --git a/scripts/kconfig/confdata.c b/scripts/kconfig/confdata.c
index 992575f1e976..d387a4f08cef 100644
--- a/scripts/kconfig/confdata.c
+++ b/scripts/kconfig/confdata.c
@@ -341,6 +341,61 @@ static ssize_t compat_getline(char **lineptr, size_t *n, FILE *stream)
 	return -1;
 }
 
+int conf_read_list_unknown(void)
+{
+	FILE *in = NULL;
+	size_t line_asize = 0;
+	char *line = NULL;
+	char *p, *p2;
+	struct symbol *sym;
+
+	conf_filename = conf_get_configname();
+	in = zconf_fopen(conf_filename);
+	if (!in)
+		return -1;
+
+	while (compat_getline(&line, &line_asize, in) != -1) {
+		conf_lineno++;
+		sym = NULL;
+		if (line[0] == '#') {
+			if (memcmp(line + 2, CONFIG_, strlen(CONFIG_)))
+				continue;
+			p = strchr(line + 2 + strlen(CONFIG_), ' ');
+			if (!p)
+				continue;
+			*p++ = 0;
+			sym = sym_find(line + 2 + strlen(CONFIG_));
+			if (!sym) {
+				conf_warning("unknown unset symbol: %s",
+					     line + 2 + strlen(CONFIG_));
+				continue;
+			}
+		} else if (memcmp(line, CONFIG_, strlen(CONFIG_)) == 0) {
+			p = strchr(line + strlen(CONFIG_), '=');
+			if (!p)
+				continue;
+			*p++ = 0;
+			p2 = strchr(p, '\n');
+			if (p2) {
+				*p2-- = 0;
+				if (*p2 == '\r')
+					*p2 = 0;
+			}
+
+			sym = sym_find(line + strlen(CONFIG_));
+			if (!sym) {
+				conf_warning("unknown symbol: %s",
+					     line + strlen(CONFIG_));
+				continue;
+			}
+		}
+	}
+
+	free(line);
+	fclose(in);
+	return conf_warnings;
+}
+
 int conf_read_simple(const char *name, int def)
 {
 	FILE *in = NULL;
diff --git a/scripts/kconfig/lkc_proto.h b/scripts/kconfig/lkc_proto.h
index edd1e617b25c..bb60b1669750 100644
--- a/scripts/kconfig/lkc_proto.h
+++ b/scripts/kconfig/lkc_proto.h
@@ -5,6 +5,7 @@
 void conf_parse(const char *name);
 int conf_read(const char *name);
 int conf_read_simple(const char *name, int);
+int conf_read_list_unknown(void);
 int conf_write_defconfig(const char *name);
 int conf_write(const char *name);
 int conf_write_autoconf(int overwrite);
-- 
2.41.0.694.ge786442a9b-goog