[tor-commits] [tor/master] Allow struct_magic to be disabled.

[nickm at torproject.org]

commit 419ba97df5bd168bf773478270c0043f20328e15
Author: Nick Mathewson <nickm at torproject.org>
Date:   Sun Dec 15 18:42:01 2019 -0500

    Allow struct_magic to be disabled.
    
    When a subsystem is disabled, there will be no corresponding object
    allocated, and no magic numbers on it.
---
 src/lib/conf/conftypes.h    |  3 +++
 src/lib/confmgt/structvar.c | 22 ++++++++++++++++++++--
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/lib/conf/conftypes.h b/src/lib/conf/conftypes.h
index 44171068a..52f9fceb2 100644
--- a/src/lib/conf/conftypes.h
+++ b/src/lib/conf/conftypes.h
@@ -131,6 +131,9 @@ typedef struct struct_member_t {
  *
  * These 'magic numbers' are 32-bit values used to tag objects to make sure
  * that they have the correct type.
+ *
+ * If all fields in this structure are zero or 0, the magic-number check is
+ * not performed.
  */
 typedef struct struct_magic_decl_t {
   /** The name of the structure */
diff --git a/src/lib/confmgt/structvar.c b/src/lib/confmgt/structvar.c
index de678d18c..a2411477d 100644
--- a/src/lib/confmgt/structvar.c
+++ b/src/lib/confmgt/structvar.c
@@ -30,13 +30,28 @@
 #include <stddef.h>
 
 /**
+ * Return true iff all fields on <b>decl</b> are NULL or 0, indicating that
+ * there is no object or no magic number to check.
+ **/
+static inline bool
+magic_is_null(const struct_magic_decl_t *decl)
+{
+  return decl->typename == NULL &&
+    decl->magic_offset == 0 &&
+    decl->magic_val == 0;
+}
+
+/**
  * Set the 'magic number' on <b>object</b> to correspond to decl.
  **/
 void
 struct_set_magic(void *object, const struct_magic_decl_t *decl)
 {
-  tor_assert(object);
   tor_assert(decl);
+  if (magic_is_null(decl))
+    return;
+
+  tor_assert(object);
   uint32_t *ptr = STRUCT_VAR_P(object, decl->magic_offset);
   *ptr = decl->magic_val;
 }
@@ -47,8 +62,11 @@ struct_set_magic(void *object, const struct_magic_decl_t *decl)
 void
 struct_check_magic(const void *object, const struct_magic_decl_t *decl)
 {
-  tor_assert(object);
   tor_assert(decl);
+  if (magic_is_null(decl))
+    return;
+
+  tor_assert(object);
 
   const uint32_t *ptr = STRUCT_VAR_P(object, decl->magic_offset);
   tor_assertf(*ptr == decl->magic_val,