From 40a1eebde6be7ac3f1885147fc24e06ad1da260c Mon Sep 17 00:00:00 2001
From: David Herrmann <dh.herrmann@gmail.com>
Date: Fri, 22 Aug 2014 13:55:57 +0200
Subject: [PATCH] shared: add MAXSIZE() and use it in resolved

The MAXSIZE() macro takes two types and returns the size of the larger
one. It is much simpler to use than MAX(sizeof(A), sizeof(B)) and also
avoids any compiler-extensions, unlike CONST_MAX() and MAX() (which are
needed to avoid evaluating arguments more than once). This was suggested
by Daniele Nicolodi <daniele@grinta.net>.

Also make resolved use this macro instead of CONST_MAX(). This enhances
readability quite a bit.
---
 src/resolve/resolved-dns-stream.c | 2 +-
 src/resolve/resolved-manager.c    | 2 +-
 src/shared/macro.h                | 3 +++
 src/test/test-util.c              | 4 ++++
 4 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/resolve/resolved-dns-stream.c b/src/resolve/resolved-dns-stream.c
index 8b3a3ced4b..8aad5e4df1 100644
--- a/src/resolve/resolved-dns-stream.c
+++ b/src/resolve/resolved-dns-stream.c
@@ -64,7 +64,7 @@ static int dns_stream_complete(DnsStream *s, int error) {
 static int dns_stream_identify(DnsStream *s) {
         union {
                 struct cmsghdr header; /* For alignment */
-                uint8_t buffer[CMSG_SPACE(CONST_MAX(sizeof(struct in_pktinfo), sizeof(struct in6_pktinfo)))
+                uint8_t buffer[CMSG_SPACE(MAXSIZE(struct in_pktinfo, struct in6_pktinfo))
                                + EXTRA_CMSG_SPACE /* kernel appears to require extra space */];
         } control;
         struct msghdr mh = {};
diff --git a/src/resolve/resolved-manager.c b/src/resolve/resolved-manager.c
index 56baf8730d..659b1dacc8 100644
--- a/src/resolve/resolved-manager.c
+++ b/src/resolve/resolved-manager.c
@@ -841,7 +841,7 @@ int manager_recv(Manager *m, int fd, DnsProtocol protocol, DnsPacket **ret) {
         _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
         union {
                 struct cmsghdr header; /* For alignment */
-                uint8_t buffer[CMSG_SPACE(CONST_MAX(sizeof(struct in_pktinfo), sizeof(struct in6_pktinfo)))
+                uint8_t buffer[CMSG_SPACE(MAXSIZE(struct in_pktinfo, struct in6_pktinfo))
                                + CMSG_SPACE(int) /* ttl/hoplimit */
                                + EXTRA_CMSG_SPACE /* kernel appears to require extra buffer space */];
         } control;
diff --git a/src/shared/macro.h b/src/shared/macro.h
index 179b24c983..43fa3e556f 100644
--- a/src/shared/macro.h
+++ b/src/shared/macro.h
@@ -149,6 +149,9 @@ static inline unsigned long ALIGN_POWER2(unsigned long u) {
                 ((_A) > (_B)) ? (_A) : (_B),                            \
                 (void)0))
 
+/* takes two types and returns the size of the larger one */
+#define MAXSIZE(A, B) (sizeof(union _packed_ { typeof(A) a; typeof(B) b; }))
+
 #define MAX3(x,y,z)                                     \
         __extension__ ({                                \
                         const typeof(x) _c = MAX(x,y);  \
diff --git a/src/test/test-util.c b/src/test/test-util.c
index ac1afce86b..34d5f2ed7d 100644
--- a/src/test/test-util.c
+++ b/src/test/test-util.c
@@ -90,6 +90,10 @@ static void test_max(void) {
         assert_se(val1.a == 100);
         assert_se(MAX(++d, 0) == 1);
         assert_se(d == 1);
+
+        assert_cc(MAXSIZE(char[3], uint16_t) == 3);
+        assert_cc(MAXSIZE(char[3], uint32_t) == 4);
+        assert_cc(MAXSIZE(char, long) == sizeof(long));
 }
 
 static void test_first_word(void) {