systemctl: be smarter when mangling snapshot names

For "systemctl snapshot" it makes no sense to complete an incomplete
name with ".service" as we previously did, use ".snapshot" instead.
Also, don't bother with mount units or suchlike, we know that this must
be a snapshot and hence is the only sane way for completion.

src/shared/unit-name.c

@@ -506,6 +506,36 @@ char *unit_name_mangle(const char *name) {
         return r;
 }
 
+char *snapshot_name_mangle(const char *name) {
+        char *r, *t;
+        const char *f;
+
+        assert(name);
+
+        /* Similar to unit_name_mangle(), but is called when we know
+         * that this is about snapshot units. */
+
+        r = new(char, strlen(name) * 4 + 1 + sizeof(".snapshot")-1);
+        if (!r)
+                return NULL;
+
+        for (f = name, t = r; *f; f++) {
+                if (*f == '/')
+                        *(t++) = '-';
+                else if (!strchr(VALID_CHARS, *f))
+                        t = do_escape_char(*f, t);
+                else
+                        *(t++) = *f;
+        }
+
+        if (!endswith(name, ".snapshot"))
+                strcpy(t, ".snapshot");
+        else
+                *t = 0;
+
+        return r;
+}
+
 UnitType unit_name_to_type(const char *n) {
         const char *e;
 

src/shared/unit-name.h

@@ -94,3 +94,4 @@ char *unit_name_to_path(const char *name);
 char *unit_dbus_path_from_name(const char *name);
 
 char *unit_name_mangle(const char *name);
+char *snapshot_name_mangle(const char *name);