[dpdk-dev] [PATCH v2 1/2] ring: introduce rte_ring_get_memsize()

[Olivier Matz <olivier.matz@6wind.com>]

Add a function that returns the amount of memory occupied by a rte_ring
structure and its object table. This commit prepares the next one that
will allow to allocate a ring dynamically.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
---
 lib/librte_ring/rte_ring.c | 30 +++++++++++++++++++++++-------
 lib/librte_ring/rte_ring.h | 16 ++++++++++++++++
 2 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/lib/librte_ring/rte_ring.c b/lib/librte_ring/rte_ring.c
index 0d43a55..156fe49 100644
--- a/lib/librte_ring/rte_ring.c
+++ b/lib/librte_ring/rte_ring.c
@@ -94,6 +94,25 @@ TAILQ_HEAD(rte_ring_list, rte_ring);
 /* true if x is a power of 2 */
 #define POWEROF2(x) ((((x)-1) & (x)) == 0)
 
+/* return the size of memory occupied by a ring */
+ssize_t
+rte_ring_get_memsize(unsigned count)
+{
+	ssize_t sz;
+
+	/* count must be a power of 2 */
+	if ((!POWEROF2(count)) || (count > RTE_RING_SZ_MASK )) {
+		RTE_LOG(ERR, RING,
+			"Requested size is invalid, must be power of 2, and "
+			"do not exceed the size limit %u\n", RTE_RING_SZ_MASK);
+		return -EINVAL;
+	}
+
+	sz = sizeof(struct rte_ring) + count * sizeof(void *);
+	sz = RTE_ALIGN(sz, CACHE_LINE_SIZE);
+	return sz;
+}
+
 /* create the ring */
 struct rte_ring *
 rte_ring_create(const char *name, unsigned count, int socket_id,
@@ -102,7 +121,7 @@ rte_ring_create(const char *name, unsigned count, int socket_id,
 	char mz_name[RTE_MEMZONE_NAMESIZE];
 	struct rte_ring *r;
 	const struct rte_memzone *mz;
-	size_t ring_size;
+	ssize_t ring_size;
 	int mz_flags = 0;
 	struct rte_ring_list* ring_list = NULL;
 
@@ -129,16 +148,13 @@ rte_ring_create(const char *name, unsigned count, int socket_id,
 		return NULL;	
 	}
 
-	/* count must be a power of 2 */
-	if ((!POWEROF2(count)) || (count > RTE_RING_SZ_MASK )) {
-		rte_errno = EINVAL;
-		RTE_LOG(ERR, RING, "Requested size is invalid, must be power of 2, and "
-				"do not exceed the size limit %u\n", RTE_RING_SZ_MASK);
+	ring_size = rte_ring_get_memsize(count);
+	if (ring_size < 0) {
+		rte_errno = ring_size;
 		return NULL;
 	}
 
 	rte_snprintf(mz_name, sizeof(mz_name), "%s%s", RTE_RING_MZ_PREFIX, name);
-	ring_size = count * sizeof(void *) + sizeof(struct rte_ring);
 
 	rte_rwlock_write_lock(RTE_EAL_TAILQ_RWLOCK);
 
diff --git a/lib/librte_ring/rte_ring.h b/lib/librte_ring/rte_ring.h
index 775ea79..e8493f2 100644
--- a/lib/librte_ring/rte_ring.h
+++ b/lib/librte_ring/rte_ring.h
@@ -199,6 +199,22 @@ struct rte_ring {
 #endif
 
 /**
+ * Calculate the memory size needed for a ring
+ *
+ * This function returns the number of bytes needed for a ring, given
+ * the number of elements in it. This value is the sum of the size of
+ * the structure rte_ring and the size of the memory needed by the
+ * objects pointers. The value is aligned to a cache line size.
+ *
+ * @param count
+ *   The number of elements in the ring (must be a power of 2).
+ * @return
+ *   - The memory size needed for the ring on success.
+ *   - -EINVAL if count is not a power of 2.
+ */
+ssize_t rte_ring_get_memsize(unsigned count);
+
+/**
  * Create a new ring named *name* in memory.
  *
  * This function uses ``memzone_reserve()`` to allocate memory. Its size is
-- 
1.9.2