qemu-img: Move is_valid_option_list() to qemu-img.c and rewrite

is_valid_option_list()'s purpose is ensuring qemu-img.c's can safely
join multiple parameter strings separated by ',' like this:

        g_strdup_printf("%s,%s", params1, params2);

How it does that is anything but obvious.  A close reading of the code
reveals that it fails exactly when its argument starts with ',' or
ends with an odd number of ','.  Makes sense, actually, because when
the argument starts with ',', a separating ',' preceding it would get
escaped, and when it ends with an odd number of ',', a separating ','
following it would get escaped.

Move it to qemu-img.c and rewrite it the obvious way.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200415074927.19897-9-armbru@redhat.com>

include/qemu/option.h

@@ -33,7 +33,6 @@ const char *get_opt_value(const char *p, char **value);
 void parse_option_size(const char *name, const char *value,
                        uint64_t *ret, Error **errp);
 bool has_help_option(const char *param);
-bool is_valid_option_list(const char *param);
 
 enum QemuOptType {
     QEMU_OPT_STRING = 0,  /* no parsing (use string as-is)                        */

qemu-img.c

@@ -223,6 +223,32 @@ static bool qemu_img_object_print_help(const char *type, QemuOpts *opts)
     return true;
 }
 
+/*
+ * Is @optarg safe for accumulate_options()?
+ * It is when multiple of them can be joined together separated by ','.
+ * To make that work, @optarg must not start with ',' (or else a
+ * separating ',' preceding it gets escaped), and it must not end with
+ * an odd number of ',' (or else a separating ',' following it gets
+ * escaped).
+ */
+static bool is_valid_option_list(const char *optarg)
+{
+    size_t len = strlen(optarg);
+    size_t i;
+
+    if (optarg[0] == ',') {
+        return false;
+    }
+
+    for (i = len; i > 0 && optarg[i - 1] == ','; i--) {
+    }
+    if ((len - i) % 2) {
+        return false;
+    }
+
+    return true;
+}
+
 static int accumulate_options(char **options, char *optarg)
 {
     char *new_options;

util/qemu-option.c

@@ -165,28 +165,6 @@ void parse_option_size(const char *name, const char *value,
     *ret = size;
 }
 
-bool is_valid_option_list(const char *p)
-{
-    char *value = NULL;
-    bool result = false;
-
-    while (*p) {
-        p = get_opt_value(p, &value);
-        if ((*p && !*++p) ||
-            (!*value || *value == ',')) {
-            goto out;
-        }
-
-        g_free(value);
-        value = NULL;
-    }
-
-    result = true;
-out:
-    g_free(value);
-    return result;
-}
-
 static const char *opt_type_to_string(enum QemuOptType type)
 {
     switch (type) {