net: buf: add max allocation size to allocation info

Previously, there was no way to determine maximum number of bytes
that can be allocated using only net_buf structure. This commit
introduces such field.

Moreover, this commit fixes an issue where allocation of less than
maximum number of bytes from a fixed buffer pool would set buffer's
size to this number instead of the whole buffer size.

Signed-off-by: Konrad Derda <[email protected]>

include/zephyr/net/buf.h

@@ -965,6 +965,7 @@ struct net_buf_data_cb {
 struct net_buf_data_alloc {
 	const struct net_buf_data_cb *cb;
 	void *alloc_data;
+	size_t max_alloc_size;
 };
 
 /**
@@ -1078,7 +1079,6 @@ extern const struct net_buf_data_alloc net_buf_heap_alloc;
 					 _destroy)
 
 struct net_buf_pool_fixed {
-	size_t data_size;
 	uint8_t *data_pool;
 };
 
@@ -1118,12 +1118,12 @@ extern const struct net_buf_data_cb net_buf_fixed_cb;
 	_NET_BUF_ARRAY_DEFINE(_name, _count, _ud_size);                        \
 	static uint8_t __noinit net_buf_data_##_name[_count][_data_size] __net_buf_align; \
 	static const struct net_buf_pool_fixed net_buf_fixed_##_name = {       \
-		.data_size = _data_size,                                       \
 		.data_pool = (uint8_t *)net_buf_data_##_name,                  \
 	};                                                                     \
 	static const struct net_buf_data_alloc net_buf_fixed_alloc_##_name = { \
 		.cb = &net_buf_fixed_cb,                                       \
 		.alloc_data = (void *)&net_buf_fixed_##_name,                  \
+		.max_alloc_size = _data_size,                                  \
 	};                                                                     \
 	static STRUCT_SECTION_ITERABLE(net_buf_pool, _name) =                  \
 		NET_BUF_POOL_INITIALIZER(_name, &net_buf_fixed_alloc_##_name,  \
@@ -1164,6 +1164,7 @@ extern const struct net_buf_data_cb net_buf_var_cb;
 	static const struct net_buf_data_alloc net_buf_data_alloc_##_name = {  \
 		.cb = &net_buf_var_cb,                                         \
 		.alloc_data = &net_buf_mem_pool_##_name,                       \
+		.max_alloc_size = 0,                                           \
 	};                                                                     \
 	static STRUCT_SECTION_ITERABLE(net_buf_pool, _name) =                  \
 		NET_BUF_POOL_INITIALIZER(_name, &net_buf_data_alloc_##_name,   \

subsys/net/buf.c

@@ -151,9 +151,9 @@ static uint8_t *fixed_data_alloc(struct net_buf *buf, size_t *size,
 	struct net_buf_pool *pool = net_buf_pool_get(buf->pool_id);
 	const struct net_buf_pool_fixed *fixed = pool->alloc->alloc_data;
 
-	*size = MIN(fixed->data_size, *size);
+	*size = pool->alloc->max_alloc_size;
 
-	return fixed->data_pool + fixed->data_size * net_buf_id(buf);
+	return fixed->data_pool + *size * net_buf_id(buf);
 }
 
 static void fixed_data_unref(struct net_buf *buf, uint8_t *data)
@@ -203,6 +203,7 @@ static const struct net_buf_data_cb net_buf_heap_cb = {
 
 const struct net_buf_data_alloc net_buf_heap_alloc = {
 	.cb = &net_buf_heap_cb,
+	.max_alloc_size = 0,
 };
 
 #endif /* K_HEAP_MEM_POOL_SIZE > 0 */
@@ -345,18 +346,14 @@ struct net_buf *net_buf_alloc_fixed_debug(struct net_buf_pool *pool,
 					  k_timeout_t timeout, const char *func,
 					  int line)
 {
-	const struct net_buf_pool_fixed *fixed = pool->alloc->alloc_data;
-
-	return net_buf_alloc_len_debug(pool, fixed->data_size, timeout, func,
+	return net_buf_alloc_len_debug(pool, pool->alloc->max_alloc_size, timeout, func,
 				       line);
 }
 #else
 struct net_buf *net_buf_alloc_fixed(struct net_buf_pool *pool,
 				    k_timeout_t timeout)
 {
-	const struct net_buf_pool_fixed *fixed = pool->alloc->alloc_data;
-
-	return net_buf_alloc_len(pool, fixed->data_size, timeout);
+	return net_buf_alloc_len(pool, pool->alloc->max_alloc_size, timeout);
 }
 #endif
 
@@ -659,6 +656,7 @@ size_t net_buf_append_bytes(struct net_buf *buf, size_t len,
 	struct net_buf *frag = net_buf_frag_last(buf);
 	size_t added_len = 0;
 	const uint8_t *value8 = value;
+	size_t max_size;
 
 	do {
 		uint16_t count = MIN(len, net_buf_tailroom(frag));
@@ -681,7 +679,10 @@ size_t net_buf_append_bytes(struct net_buf *buf, size_t len,
 			 * been provided.
 			 */
 			pool = net_buf_pool_get(buf->pool_id);
-			frag = net_buf_alloc_len(pool, len, timeout);
+			max_size = pool->alloc->max_alloc_size;
+			frag = net_buf_alloc_len(pool,
+						 max_size ? MIN(len, max_size) : len,
+						 timeout);
 		}
 
 		if (!frag) {