r3553: Allow talloc_reference to take a NULL pointer for the "ptr" argument.

This allows potentially NULL pointers to be referenced, without an if ()
for every use.  (previously, it would segfault).

Update doco, and allow talloc_unlink to match.

Andrew Bartlett
(This used to be commit 59757c7f9d0e08e3acacfb3116f6205057d5b119)

3 files changed, 24 insertions, 3 deletions

diff --git a/source4/lib/talloc.c b/source4/lib/talloc.c
index 131edfcb81..239958258b 100644
--- a/source4/lib/talloc.c
+++ b/source4/lib/talloc.c
@@ -222,9 +222,13 @@ static int talloc_reference_destructor(void *ptr)
 */
 void *talloc_reference(const void *context, const void *ptr)
 {
-	struct talloc_chunk *tc = talloc_chunk_from_ptr(ptr);
+	struct talloc_chunk *tc;
 	struct talloc_reference_handle *handle;
+	if (ptr == NULL) return NULL;
+
+	tc = talloc_chunk_from_ptr(ptr);
 	handle = talloc_named_const(context, sizeof(*handle), TALLOC_MAGIC_REFERENCE);
+
 	if (handle == NULL) return NULL;
 
 	/* note that we hang the destructor off the handle, not the
@@ -273,6 +277,10 @@ int talloc_unlink(const void *context, void *ptr)
 	struct talloc_chunk *tc_p, *new_p;
 	void *new_parent;
 
+	if (ptr == NULL) {
+		return -1;
+	}
+
 	if (context == NULL) {
 		context = null_context;
 	}
diff --git a/source4/torture/local/talloc.c b/source4/torture/local/talloc.c
index 348b037753..2eedb2b9b0 100644
--- a/source4/torture/local/talloc.c
+++ b/source4/torture/local/talloc.c
@@ -117,6 +117,11 @@ static BOOL test_ref1(void)
 	talloc_free(r1);
 	talloc_report_full(NULL, stdout);
 
+	printf("Testing NULL\n");
+	if (talloc_reference(root, NULL)) {
+		return False;
+	}
+
 	CHECK_BLOCKS(root, 1);
 
 	CHECK_SIZE(root, 0);
@@ -478,7 +483,12 @@ static BOOL test_misc(void)
 	talloc_unlink(NULL, p2);
 	talloc_unlink(root, p1);
 
-	
+	/* Test that talloc_unlink is a no-op */
+
+	if (talloc_unlink(root, NULL) != -1) {
+		printf("failed: talloc_unlink(root, NULL) == -1\n");
+		return False;
+	}
 
 	talloc_report(root, stdout);
 	talloc_report(NULL, stdout);
diff --git a/talloc_guide.txt b/talloc_guide.txt
index a794cdffbe..b3b148d476 100644
--- a/talloc_guide.txt
+++ b/talloc_guide.txt
@@ -122,6 +122,8 @@ The return value of talloc_reference() is always the original pointer
 which case it will return NULL (each additional reference consumes
 around 48 bytes of memory on intel x86 platforms).
 
+If "ptr" is NULL, then the function is a no-op, and simply returns NULL.
+
 After creating a reference you can free it in one of the following
 ways:
 
@@ -144,7 +146,8 @@ context passed must either be a context used in talloc_reference()
 with this pointer, or must be a direct parent of ptr. 
 
 Note that if the parent has already been removed using talloc_free()
-then this function will fail and will return -1.
+then this function will fail and will return -1.  Likewise, if "ptr"
+is NULL, then the function will make no modifications and return -1.
 
 Usually you can just use talloc_free() instead of talloc_unlink(), but
 sometimes it is useful to have the additional control on which parent