util-lib: various improvements to kernel command line parsing

This improves kernel command line parsing in a number of ways:

a) An kernel option "foo_bar=xyz" is now considered equivalent to
   "foo-bar-xyz", i.e. when comparing kernel command line option names "-" and
   "_" are now considered equivalent (this only applies to the option names
   though, not the option values!). Most of our kernel options used "-" as word
   separator in kernel command line options so far, but some used "_". With
   this change, which was a source of confusion for users (well, at least of
   one user: myself, I just couldn't remember that it's systemd.debug-shell,
   not systemd.debug_shell). Considering both as equivalent is inspired how
   modern kernel module loading normalizes all kernel module names to use
   underscores now too.

b) All options previously using a dash for separating words in kernel command
   line options now use an underscore instead, in all documentation and in
   code. Since a) has been implemented this should not create any compatibility
   problems, but normalizes our documentation and our code.

c) All kernel command line options which take booleans (or are boolean-like)
   have been reworked so that "foobar" (without argument) is now equivalent to
   "foobar=1" (but not "foobar=0"), thus normalizing the handling of our
   boolean arguments. Specifically this means systemd.debug-shell and
   systemd_debug_shell=1 are now entirely equivalent.

d) All kernel command line options which take an argument, and where no
   argument is specified will now result in a log message. e.g. passing just
   "systemd.unit" will no result in a complain that it needs an argument. This
   is implemented in the proc_cmdline_missing_value() function.

e) There's now a call proc_cmdline_get_bool() similar to proc_cmdline_get_key()
   that parses booleans (following the logic explained in c).

f) The proc_cmdline_parse() call's boolean argument has been replaced by a new
   flags argument that takes a common set of bits with proc_cmdline_get_key().

g) All kernel command line APIs now begin with the same "proc_cmdline_" prefix.

h) There are now tests for much of this. Yay!

4 files changed, 162 insertions, 68 deletions

diff --git a/src/basic/cgroup-util.c b/src/basic/cgroup-util.c
index dc13025115..d2d18f13f0 100644
--- a/src/basic/cgroup-util.c
+++ b/src/basic/cgroup-util.c
@@ -2361,6 +2361,7 @@ int cg_enable_everywhere(CGroupMask supported, CGroupMask mask, const char *p) {
 bool cg_is_unified_wanted(void) {
         static thread_local int wanted = -1;
         int r, unified;
+        bool b;
 
         /* If the hierarchy is already mounted, then follow whatever
          * was chosen for it. */
@@ -2374,20 +2375,11 @@ bool cg_is_unified_wanted(void) {
         if (wanted >= 0)
                 return wanted;
 
-        r = get_proc_cmdline_key("systemd.unified_cgroup_hierarchy", NULL);
-        if (r > 0)
-                return (wanted = true);
-        else {
-                _cleanup_free_ char *value = NULL;
-
-                r = get_proc_cmdline_key("systemd.unified_cgroup_hierarchy=", &value);
-                if (r < 0)
-                        return false;
-                if (r == 0)
-                        return (wanted = false);
+        r = proc_cmdline_get_bool("systemd.unified_cgroup_hierarchy", &b);
+        if (r < 0)
+                return false;
 
-                return (wanted = parse_boolean(value) > 0);
-        }
+        return (wanted = r > 0 ? b : false);
 }
 
 bool cg_is_legacy_wanted(void) {
@@ -2397,6 +2389,7 @@ bool cg_is_legacy_wanted(void) {
 bool cg_is_unified_systemd_controller_wanted(void) {
         static thread_local int wanted = -1;
         int r, unified;
+        bool b;
 
         /* If the unified hierarchy is requested in full, no need to
          * bother with this. */
@@ -2415,23 +2408,11 @@ bool cg_is_unified_systemd_controller_wanted(void) {
         if (wanted >= 0)
                 return wanted;
 
-        r = get_proc_cmdline_key("systemd.legacy_systemd_cgroup_controller", NULL);
-        if (r > 0)
-                wanted = false;
-        else {
-                _cleanup_free_ char *value = NULL;
-
-                r = get_proc_cmdline_key("systemd.legacy_systemd_cgroup_controller=", &value);
-                if (r < 0)
-                        return false;
-
-                if (r == 0)
-                        wanted = false;
-                else
-                        wanted = parse_boolean(value) <= 0;
-        }
+        r = proc_cmdline_get_bool("systemd.legacy_systemd_cgroup_controller", &b);
+        if (r < 0)
+                return false;
 
-        return wanted;
+        return (wanted = r > 0 ? b : false);
 }
 
 bool cg_is_legacy_systemd_controller_wanted(void) {
diff --git a/src/basic/log.c b/src/basic/log.c
index 557212c022..1362b1c086 100644
--- a/src/basic/log.c
+++ b/src/basic/log.c
@@ -981,24 +981,30 @@ static int parse_proc_cmdline_item(const char *key, const char *value, void *dat
         if (streq(key, "debug") && !value)
                 log_set_max_level(LOG_DEBUG);
 
-        else if (streq(key, "systemd.log_target") && value) {
+        else if (proc_cmdline_key_streq(key, "systemd.log_target")) {
+
+                if (proc_cmdline_value_missing(key, value))
+                        return 0;
 
                 if (log_set_target_from_string(value) < 0)
                         log_warning("Failed to parse log target '%s'. Ignoring.", value);
 
-        } else if (streq(key, "systemd.log_level") && value) {
+        } else if (proc_cmdline_key_streq(key, "systemd.log_level")) {
+
+                if (proc_cmdline_value_missing(key, value))
+                        return 0;
 
                 if (log_set_max_level_from_string(value) < 0)
                         log_warning("Failed to parse log level '%s'. Ignoring.", value);
 
-        } else if (streq(key, "systemd.log_color") && value) {
+        } else if (proc_cmdline_key_streq(key, "systemd.log_color")) {
 
-                if (log_show_color_from_string(value) < 0)
+                if (log_show_color_from_string(value ?: "1") < 0)
                         log_warning("Failed to parse log color setting '%s'. Ignoring.", value);
 
-        } else if (streq(key, "systemd.log_location") && value) {
+        } else if (proc_cmdline_key_streq(key, "systemd.log_location")) {
 
-                if (log_show_location_from_string(value) < 0)
+                if (log_show_location_from_string(value ?: "1") < 0)
                         log_warning("Failed to parse log location setting '%s'. Ignoring.", value);
         }
 
@@ -1009,10 +1015,9 @@ void log_parse_environment(void) {
         const char *e;
 
         if (get_ctty_devnr(0, NULL) < 0)
-                /* Only try to read the command line in daemons.
-                   We assume that anything that has a controlling
-                   tty is user stuff. */
-                (void) parse_proc_cmdline(parse_proc_cmdline_item, NULL, true);
+                /* Only try to read the command line in daemons.  We assume that anything that has a controlling tty is
+                   user stuff. */
+                (void) proc_cmdline_parse(parse_proc_cmdline_item, NULL, PROC_CMDLINE_STRIP_RD_PREFIX);
 
         e = secure_getenv("SYSTEMD_LOG_TARGET");
         if (e && log_set_target_from_string(e) < 0)
diff --git a/src/basic/proc-cmdline.c b/src/basic/proc-cmdline.c
index 98c94ed5e2..6ecb6c3f0d 100644
--- a/src/basic/proc-cmdline.c
+++ b/src/basic/proc-cmdline.c
@@ -56,9 +56,8 @@ int proc_cmdline(char **ret) {
                 return read_one_line_file("/proc/cmdline", ret);
 }
 
-int parse_proc_cmdline(int (*parse_item)(const char *key, const char *value, void *data),
-                       void *data,
-                       bool strip_prefix) {
+int proc_cmdline_parse(proc_cmdline_parse_t parse_item, void *data, unsigned flags) {
+
         _cleanup_free_ char *line = NULL;
         const char *p;
         int r;
@@ -72,7 +71,7 @@ int parse_proc_cmdline(int (*parse_item)(const char *key, const char *value, voi
         p = line;
         for (;;) {
                 _cleanup_free_ char *word = NULL;
-                char *value = NULL, *unprefixed;
+                char *value, *key, *q;
 
                 r = extract_first_word(&p, &word, NULL, EXTRACT_QUOTES|EXTRACT_RELAX);
                 if (r < 0)
@@ -80,17 +79,23 @@ int parse_proc_cmdline(int (*parse_item)(const char *key, const char *value, voi
                 if (r == 0)
                         break;
 
-                /* Filter out arguments that are intended only for the
-                 * initrd */
-                unprefixed = startswith(word, "rd.");
-                if (unprefixed && !in_initrd())
-                        continue;
+                key = word;
+
+                /* Filter out arguments that are intended only for the initrd */
+                q = startswith(word, "rd.");
+                if (q) {
+                        if (!in_initrd())
+                                continue;
+
+                        if (flags & PROC_CMDLINE_STRIP_RD_PREFIX)
+                                key = q;
+                }
 
-                value = strchr(word, '=');
+                value = strchr(key, '=');
                 if (value)
                         *(value++) = 0;
 
-                r = parse_item(strip_prefix && unprefixed ? unprefixed : word, value, data);
+                r = parse_item(key, value, data);
                 if (r < 0)
                         return r;
         }
@@ -98,13 +103,64 @@ int parse_proc_cmdline(int (*parse_item)(const char *key, const char *value, voi
         return 0;
 }
 
-int get_proc_cmdline_key(const char *key, char **value) {
+static bool relaxed_equal_char(char a, char b) {
+
+        return a == b ||
+                (a == '_' && b == '-') ||
+                (a == '-' && b == '_');
+}
+
+char *proc_cmdline_key_startswith(const char *s, const char *prefix) {
+
+        assert(s);
+        assert(prefix);
+
+        /* Much like startswith(), but considers "-" and "_" the same */
+
+        for (; *prefix != 0; s++, prefix++)
+                if (!relaxed_equal_char(*s, *prefix))
+                        return NULL;
+
+        return (char*) s;
+}
+
+bool proc_cmdline_key_streq(const char *x, const char *y) {
+        assert(x);
+        assert(y);
+
+        /* Much like streq(), but considers "-" and "_" the same */
+
+        for (; *x != 0 || *y != 0; x++, y++)
+                if (!relaxed_equal_char(*x, *y))
+                        return false;
+
+        return true;
+}
+
+int proc_cmdline_get_key(const char *key, unsigned flags, char **value) {
         _cleanup_free_ char *line = NULL, *ret = NULL;
         bool found = false;
         const char *p;
         int r;
 
-        assert(key);
+        /* Looks for a specific key on the kernel command line. Supports two modes:
+         *
+         * a) The "value" parameter is used. In this case a parameter beginning with the "key" string followed by "="
+         *    is searched, and the value following this is returned in "value".
+         *
+         * b) as above, but the PROC_CMDLINE_VALUE_OPTIONAL flag is set. In this case if the the key is found as a
+         *    separate word (i.e. not followed by "=" but instead by whitespace or the end of the command line), then
+         *    this is also accepted, and "value" is returned as NULL.
+         *
+         * c) The "value" parameter is NULL. In this case a search for the exact "key" parameter is performed.
+         *
+         * In all three cases, > 0 is returned if the key is found, 0 if not.*/
+
+        if (isempty(key))
+                return -EINVAL;
+
+        if ((flags & PROC_CMDLINE_VALUE_OPTIONAL) && !value)
+                return -EINVAL;
 
         r = proc_cmdline(&line);
         if (r < 0)
@@ -121,21 +177,26 @@ int get_proc_cmdline_key(const char *key, char **value) {
                 if (r == 0)
                         break;
 
-                /* Filter out arguments that are intended only for the
-                 * initrd */
+                /* Automatically filter out arguments that are intended only for the initrd, if we are not in the
+                 * initrd. */
                 if (!in_initrd() && startswith(word, "rd."))
                         continue;
 
                 if (value) {
-                        e = startswith(word, key);
+                        e = proc_cmdline_key_startswith(word, key);
                         if (!e)
                                 continue;
 
-                        r = free_and_strdup(&ret, e);
-                        if (r < 0)
-                                return r;
+                        if (*e == '=') {
+                                r = free_and_strdup(&ret, e+1);
+                                if (r < 0)
+                                        return r;
+
+                                found = true;
+
+                        } else if (*e == 0 && (flags & PROC_CMDLINE_VALUE_OPTIONAL))
+                                found = true;
 
-                        found = true;
                 } else {
                         if (streq(word, key))
                                 found = true;
@@ -148,20 +209,42 @@ int get_proc_cmdline_key(const char *key, char **value) {
         }
 
         return found;
+}
+
+int proc_cmdline_get_bool(const char *key, bool *ret) {
+        _cleanup_free_ char *v = NULL;
+        int r;
+
+        assert(ret);
+
+        r = proc_cmdline_get_key(key, PROC_CMDLINE_VALUE_OPTIONAL, &v);
+        if (r < 0)
+                return r;
+        if (r == 0) {
+                *ret = false;
+                return 0;
+        }
+
+        if (v) { /* parameter passed */
+                r = parse_boolean(v);
+                if (r < 0)
+                        return r;
+                *ret = r;
+        } else /* no parameter passed */
+                *ret = true;
 
+        return 1;
 }
 
 int shall_restore_state(void) {
-        _cleanup_free_ char *value = NULL;
+        bool ret;
         int r;
 
-        r = get_proc_cmdline_key("systemd.restore_state=", &value);
+        r = proc_cmdline_get_bool("systemd.restore_state", &ret);
         if (r < 0)
                 return r;
-        if (r == 0)
-                return true;
 
-        return parse_boolean(value);
+        return r > 0 ? ret : true;
 }
 
 static const char * const rlmap[] = {
diff --git a/src/basic/proc-cmdline.h b/src/basic/proc-cmdline.h
index 6d6ee95c11..ebfed355e9 100644
--- a/src/basic/proc-cmdline.h
+++ b/src/basic/proc-cmdline.h
@@ -19,11 +19,36 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
+#include <stdbool.h>
+
+#include "log.h"
+
+enum {
+        PROC_CMDLINE_STRIP_RD_PREFIX = 1,
+        PROC_CMDLINE_VALUE_OPTIONAL = 2,
+};
+
+typedef int (*proc_cmdline_parse_t)(const char *key, const char *value, void *data);
+
 int proc_cmdline(char **ret);
-int parse_proc_cmdline(int (*parse_item)(const char *key, const char *value, void *data),
-                       void *data,
-                       bool strip_prefix);
-int get_proc_cmdline_key(const char *parameter, char **value);
+
+int proc_cmdline_parse(const proc_cmdline_parse_t parse, void *userdata, unsigned flags);
+
+int proc_cmdline_get_key(const char *parameter, unsigned flags, char **value);
+int proc_cmdline_get_bool(const char *key, bool *ret);
+
+char *proc_cmdline_key_startswith(const char *s, const char *prefix);
+bool proc_cmdline_key_streq(const char *x, const char *y);
 
 int shall_restore_state(void);
 const char* runlevel_to_target(const char *rl);
+
+/* A little helper call, to be used in proc_cmdline_parse_t callbacks */
+static inline bool proc_cmdline_value_missing(const char *key, const char *value) {
+        if (!value) {
+                log_warning("Missing argument for %s= kernel command line switch, ignoring.", key);
+                return true;
+        }
+
+        return false;
+}