From a0db25e25b5691e4fc0afa5f5a9a8d1ce586decf Mon Sep 17 00:00:00 2001
From: =?utf8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Sun, 16 Oct 2016 19:23:35 -0400
Subject: [PATCH] tree-wide: introduce free_and_replace helper

It's a common pattern, so add a helper for it. A macro is necessary
because a function that takes a pointer to a pointer would be type specific,
similarly to cleanup functions. Seems better to use a macro.
---
 coccinelle/free_and_replace.cocci | 15 +++++++++++++++
 src/basic/alloc-util.h            |  8 ++++++++
 src/basic/fs-util.c               |  8 ++------
 src/basic/path-util.c             |  4 +---
 4 files changed, 26 insertions(+), 9 deletions(-)
 create mode 100644 coccinelle/free_and_replace.cocci

diff --git a/coccinelle/free_and_replace.cocci b/coccinelle/free_and_replace.cocci
new file mode 100644
index 000000000..9dcdbf4d4
--- /dev/null
+++ b/coccinelle/free_and_replace.cocci
@@ -0,0 +1,15 @@
+@@
+expression p, q;
+@@
+- free(p);
+- p = q;
+- q = NULL;
+- return 0;
++ return free_and_replace(p, q);
+@@
+expression p, q;
+@@
+- free(p);
+- p = q;
+- q = NULL;
++ free_and_replace(p, q);
diff --git a/src/basic/alloc-util.h b/src/basic/alloc-util.h
index ceeee519b..a44dd473c 100644
--- a/src/basic/alloc-util.h
+++ b/src/basic/alloc-util.h
@@ -43,6 +43,14 @@ static inline void *mfree(void *memory) {
         return NULL;
 }
 
+#define free_and_replace(a, b)                  \
+        ({                                      \
+                free(a);                        \
+                (a) = (b);                      \
+                (b) = NULL;                     \
+                0;                              \
+        })
+
 void* memdup(const void *p, size_t l) _alloc_(2);
 
 static inline void freep(void *p) {
diff --git a/src/basic/fs-util.c b/src/basic/fs-util.c
index 60925f2ac..55f606ceb 100644
--- a/src/basic/fs-util.c
+++ b/src/basic/fs-util.c
@@ -684,9 +684,7 @@ int chase_symlinks(const char *path, const char *_root, char **ret) {
                             !path_startswith(parent, root))
                                 return -EINVAL;
 
-                        free(done);
-                        done = parent;
-                        parent = NULL;
+                        free_and_replace(done, parent);
 
                         fd_parent = openat(fd, "..", O_CLOEXEC|O_NOFOLLOW|O_PATH);
                         if (fd_parent < 0)
@@ -730,9 +728,7 @@ int chase_symlinks(const char *path, const char *_root, char **ret) {
                                 if (fd < 0)
                                         return -errno;
 
-                                free(buffer);
-                                buffer = destination;
-                                destination = NULL;
+                                free_and_replace(buffer, destination);
 
                                 todo = buffer;
                                 free(done);
diff --git a/src/basic/path-util.c b/src/basic/path-util.c
index 3af2bd0fd..cdbb2d398 100644
--- a/src/basic/path-util.c
+++ b/src/basic/path-util.c
@@ -290,9 +290,7 @@ char **path_strv_resolve(char **l, const char *prefix) {
                         } else {
                                 /* canonicalized path goes outside of
                                  * prefix, keep the original path instead */
-                                free(u);
-                                u = orig;
-                                orig = NULL;
+                                free_and_replace(u, orig);
                         }
                 } else
                         free(t);
-- 
2.30.2