Re: [dpdk-dev] [PATCH] ixgbe: fix compile error with gcc4.4 (used RHEL 6)

[Neil Horman <nhorman@tuxdriver.com>]

On Thu, Sep 18, 2014 at 12:35:21PM +0000, Richardson, Bruce wrote:
> > -----Original Message-----
> > From: Neil Horman [mailto:nhorman@tuxdriver.com]
> > Sent: Thursday, September 18, 2014 1:25 PM
> > To: Thomas Monjalon
> > Cc: Richardson, Bruce; dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH] ixgbe: fix compile error with gcc4.4 (used RHEL
> > 6)
> > 
> > On Thu, Sep 18, 2014 at 01:09:16PM +0200, Thomas Monjalon wrote:
> > > > The refcnt field is contained within an anonymous union within the mbuf
> > > > data structure, and gcc 4.4 gives an error about an unknown field unless
> > > > the initialiser for the field is contained within extra braces.
> > > >
> > > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > >
> > > Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>
> > >
> > > Thanks Bruce, it is now applied.
> > 
> > Hang on here, we use anonymous unions all the time in RHEL6, and make
> > assignments to them frequently, and the compiler doesn't complain (see the
> > dropcount variable in sk_buff for an example).  Not saying that this is a big
> > deal, but can you explain a little more about what you're seeing when this error
> > occurs, before we just paper over it?
> > 
> 
> Originally reported on RHEL6 as a build failure. When I use gcc4.4 on Fedora 20, I get the following without this change:
> 
>   CC ixgbe_rxtx_vec.o
> == Build lib/librte_table
> /home/bruce/dpdk.org/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c: In function 'ixgbe_rxq_vec_setup':
> /home/bruce/dpdk.org/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c:726: error: unknown field 'refcnt' specified in initializer
> compilation terminated due to -Wfatal-errors.
> make[5]: *** [ixgbe_rxtx_vec.o] Error 1
> make[4]: *** [librte_pmd_ixgbe] Error 2
> make[4]: *** Waiting for unfinished jobs....
> make[3]: *** [lib] Error 2
> make[2]: *** [all] Error 2
> make[1]: *** [x86_64-native-linuxapp-gcc_install] Error 2
> make: *** [install] Error 2
> 
> Regards,
> /Bruce
> 


Thank you, I've reproduced the problem here, and you're right, it is a compiler
bug, but I really hate the idea of just throwing braces around something to shut
the compiler up, especially when the compiler has since been fixed.  Looking at
it a bit more closely it seems like the the thing to do is actually just
consistently use rte_mbuf_refcnt_set, since thats what the rte_mbuf header
documentation says to do, and protects you if the internal structure changes, as
well as prevents you from having to spread ifdef RTE_MBUF_REFCNT all over the
place.

This patch does a bit more than that too.  With a little creative typedef-ing we
don't need the anonymous union at all, and lets us just use a single refcnt
variable, and I think eliminate that odd refcnt_reserved member of the union,
that, as far as I can see, does nothing.

Thoughts?


diff --git a/app/test/test_mbuf.c b/app/test/test_mbuf.c
index 66bcbc5..5bd634e 100644
--- a/app/test/test_mbuf.c
+++ b/app/test/test_mbuf.c
@@ -760,14 +760,14 @@ test_failing_mbuf_sanity_check(void)
 
 #ifdef RTE_MBUF_REFCNT
 	badbuf = *buf;
-	badbuf.refcnt = 0;
+	rte_mbuf_refcnt_set(&badbuf, 0);
 	if (verify_mbuf_check_panics(&badbuf)) {
 		printf("Error with bad-refcnt(0) mbuf test\n");
 		return -1;
 	}
 
 	badbuf = *buf;
-	badbuf.refcnt = UINT16_MAX;
+	rte_mbuf_refcnt_set(&badbuf, UINT16_MAX);
 	if (verify_mbuf_check_panics(&badbuf)) {
 		printf("Error with bad-refcnt(MAX) mbuf test\n");
 		return -1;
diff --git a/config/common_linuxapp b/config/common_linuxapp
index 5bee910..a001231 100644
--- a/config/common_linuxapp
+++ b/config/common_linuxapp
@@ -123,7 +123,7 @@ CONFIG_RTE_LOG_HISTORY=256
 CONFIG_RTE_LIBEAL_USE_HPET=n
 CONFIG_RTE_EAL_ALLOW_INV_SOCKET_ID=n
 CONFIG_RTE_EAL_ALWAYS_PANIC_ON_ERROR=n
-CONFIG_RTE_EAL_IGB_UIO=y
+CONFIG_RTE_EAL_IGB_UIO=n
 CONFIG_RTE_EAL_VFIO=y
 
 #
@@ -381,7 +381,7 @@ CONFIG_RTE_LIBRTE_PIPELINE=y
 #
 # Compile librte_kni
 #
-CONFIG_RTE_LIBRTE_KNI=y
+CONFIG_RTE_LIBRTE_KNI=n
 CONFIG_RTE_KNI_KO_DEBUG=n
 CONFIG_RTE_KNI_VHOST=n
 CONFIG_RTE_KNI_VHOST_MAX_CACHE_SIZE=1024
diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index 1c6e115..3fca0fb 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -120,6 +120,15 @@ extern "C" {
 typedef void    *MARKER[0];   /**< generic marker for a point in a structure */
 typedef uint64_t MARKER64[0]; /**< marker that allows us to overwrite 8 bytes
                                * with a single assignment */
+
+#ifdef RTE_MBUF_REFCNT
+#ifdef RTE_MBUF_REFCNT_ATOMIC
+typedef rte_atomic16_t rte_refcnt;
+#else
+typedef uint16_t rte_refcnt;
+#endif
+#endif
+
 /**
  * The generic rte_mbuf, containing a packet mbuf.
  */
@@ -142,13 +151,9 @@ struct rte_mbuf {
 	 * or non-atomic) is controlled by the CONFIG_RTE_MBUF_REFCNT_ATOMIC
 	 * config option.
 	 */
-	union {
 #ifdef RTE_MBUF_REFCNT
-		rte_atomic16_t refcnt_atomic; /**< Atomically accessed refcnt */
-		uint16_t refcnt;              /**< Non-atomically accessed refcnt */
+	rte_refcnt refcnt;
 #endif
-		uint16_t refcnt_reserved;     /**< Do not use this field */
-	};
 	uint8_t nb_segs;          /**< Number of segments. */
 	uint8_t port;             /**< Input port. */
 
@@ -250,6 +255,7 @@ if (!(exp)) {                                                        \
 #ifdef RTE_MBUF_REFCNT
 #ifdef RTE_MBUF_REFCNT_ATOMIC
 
+
 /**
  * Adds given value to an mbuf's refcnt and returns its new value.
  * @param m
@@ -262,7 +268,7 @@ if (!(exp)) {                                                        \
 static inline uint16_t
 rte_mbuf_refcnt_update(struct rte_mbuf *m, int16_t value)
 {
-	return (uint16_t)(rte_atomic16_add_return(&m->refcnt_atomic, value));
+	return (uint16_t)(rte_atomic16_add_return(&m->refcnt, value));
 }
 
 /**
@@ -275,7 +281,7 @@ rte_mbuf_refcnt_update(struct rte_mbuf *m, int16_t value)
 static inline uint16_t
 rte_mbuf_refcnt_read(const struct rte_mbuf *m)
 {
-	return (uint16_t)(rte_atomic16_read(&m->refcnt_atomic));
+	return (uint16_t)(rte_atomic16_read(&m->refcnt));
 }
 
 /**
@@ -288,7 +294,7 @@ rte_mbuf_refcnt_read(const struct rte_mbuf *m)
 static inline void
 rte_mbuf_refcnt_set(struct rte_mbuf *m, uint16_t new_value)
 {
-	rte_atomic16_set(&m->refcnt_atomic, new_value);
+	rte_atomic16_set(&m->refcnt, new_value);
 }
 
 #else /* ! RTE_MBUF_REFCNT_ATOMIC */
diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
index 203ddf7..4a80224 100644
--- a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
+++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
@@ -722,11 +722,9 @@ ixgbe_rxq_vec_setup(struct igb_rx_queue *rxq)
 	static struct rte_mbuf mb_def = {
 		.nb_segs = 1,
 		.data_off = RTE_PKTMBUF_HEADROOM,
-#ifdef RTE_MBUF_REFCNT
-		{ .refcnt = 1, }
-#endif
 	};
 
+	rte_mbuf_refcnt_set(&mb_def, 1);
 	mb_def.buf_len = rxq->mb_pool->elt_size - sizeof(struct rte_mbuf);
 	mb_def.port = rxq->port_id;
 	rxq->mbuf_initializer = *((uint64_t *)&mb_def.rearm_data);