遍历feature_main主结构的next_arc单向链表，按照顺序为每个ARC注册结构分配索引（feature_arc_index），如果注册ARC的时候为成员arc_index_ptr附了值，将ARC索引写入此值。

将arc_name作为key，areg注册结构为value，写入arc_index_by_name的哈希中，方便之后查找。计算ARC中开始节点的数量，递增ARC索引，遍历下一个ARC注册结构。

vnet_feature_init (vlib_main_t * vm)
{vnet_feature_main_t *fm = &feature_main;vnet_feature_registration_t *freg;vnet_feature_arc_registration_t *areg;vnet_feature_constraint_registration_t *creg;u32 arc_index = 0;fm->arc_index_by_name = hash_create_string (0, sizeof (uword));areg = fm->next_arc;while (areg) {char *s;int i = 0;areg->feature_arc_index = arc_index;if (areg->arc_index_ptr)*areg->arc_index_ptr = arc_index;hash_set_mem (fm->arc_index_by_name, areg->arc_name, pointer_to_uword (areg));while ((s = areg->start_nodes[i]))i++;areg->n_start_nodes = i;areg = areg->next;arc_index++;}

按照最大的ARC索引值，分配以下的向量。

  vec_validate (fm->next_feature_by_arc, arc_index - 1);vec_validate (fm->feature_nodes, arc_index - 1);vec_validate (fm->feature_config_mains, arc_index - 1);vec_validate (fm->next_feature_by_name, arc_index - 1);vec_validate (fm->sw_if_index_has_features, arc_index - 1);vec_validate (fm->feature_count_by_sw_if_index, arc_index - 1);vec_validate (fm->next_constraint_by_arc, arc_index - 1);

遍历全局features单向链表next_feature，根据feature中的ARC名称，在哈希arc_index_by_name中找到ARC注册结构，进而找到ARC的feature链表头next_feature_by_arc[arc_index]，为索引arc_index的ARC创建feature链表。

遍历结束之后，为每个ARC创建了feature链表next_feature_by_arc[arc_index]。

  freg = fm->next_feature;while (freg) {vnet_feature_registration_t *next;uword *p = hash_get_mem (fm->arc_index_by_name, freg->arc_name);if (p == 0) {clib_warning ("Unknown feature arc '%s'", freg->arc_name);os_exit (1);}areg = uword_to_pointer (p[0], vnet_feature_arc_registration_t *);arc_index = areg->feature_arc_index;next = freg->next;freg->next_in_arc = fm->next_feature_by_arc[arc_index];fm->next_feature_by_arc[arc_index] = freg;freg = next;}

遍历全局的next_constraint链表，最终为每个ARC创建单独的constraint链表，链表头部为next_constraint_by_arc[arc_index]，最后添加的位于链表的头部。

  /* Move bulk constraints to the constraint by arc lists */creg = fm->next_constraint;while (creg) {vnet_feature_constraint_registration_t *next;uword *p = hash_get_mem (fm->arc_index_by_name, creg->arc_name);if (p == 0) {clib_warning ("Unknown feature arc '%s'", creg->arc_name);os_exit (1);}areg = uword_to_pointer (p[0], vnet_feature_arc_registration_t *);arc_index = areg->feature_arc_index;next = creg->next;creg->next_in_arc = fm->next_constraint_by_arc[arc_index];fm->next_constraint_by_arc[arc_index] = creg;creg = next;}

最后，再次遍历next_arc链表，对于每个ARC集合，检测其中的features是否满足定义的次序，如果last_in_arc不等于排序之后的最后一个feature，表明发生错误。

  areg = fm->next_arc;while (areg){vnet_feature_config_main_t *cm;vnet_config_main_t *vcm;char **features_in_order, *last_feature;arc_index = areg->feature_arc_index;cm = &fm->feature_config_mains[arc_index];vcm = &cm->config_main;if ((error = vnet_feature_arc_init (vm, vcm, areg->start_nodes, areg->n_start_nodes,areg->last_in_arc, fm->next_feature_by_arc[arc_index],fm->next_constraint_by_arc[arc_index], &fm->feature_nodes[arc_index]))) {os_exit (1);}features_in_order = fm->feature_nodes[arc_index];/* If specified, verify that the last node in the arc is actually last */if (areg->last_in_arc && vec_len (features_in_order) > 0){last_feature = features_in_order[vec_len (features_in_order) - 1];if (strncmp (areg->last_in_arc, last_feature, strlen (areg->last_in_arc)))clib_warning("WARNING: %s arc: last node is %s, but expected %s!",areg->arc_name, last_feature, areg->last_in_arc);}

为每个ARC的所有feature初始化next_feature_by_name[arc_index]哈希结构，之后可通过feature名称找到feature注册结构。

      fm->next_feature_by_name[arc_index] = hash_create_string (0, sizeof (uword));freg = fm->next_feature_by_arc[arc_index];while (freg) {hash_set_mem (fm->next_feature_by_name[arc_index], freg->node_name, pointer_to_uword (freg));freg = freg->next_in_arc;}areg = areg->next;}

显示ARC

命令：show features [verbose] 用于显示VPP系统中的注册的ARCs以及每个ARC包含的features集合。所有的信息都保存在全局结构feature_main中，其成员next_arc为保存了ARC注册信息的单向链表，以下函数遍历此链表。

static clib_error_t *
show_features_command_fn (vlib_main_t * vm,unformat_input_t * input, vlib_cli_command_t * cmd)
{vnet_feature_main_t *fm = &feature_main;vnet_feature_arc_registration_t *areg;vnet_feature_registration_t *freg;vnet_feature_registration_t *feature_regs = 0;areg = fm->next_arc;while (areg) {if (verbose)vlib_cli_output (vm, "[%2d] %s:", areg->feature_arc_index, areg->arc_name);elsevlib_cli_output (vm, "%s:", areg->arc_name);

ARC中的features链表保存在feature_main的成员next_feature_by_arc中，单向链表，next_in_arc指向下一个feature注册结构。遍历过程中将所有的feature注册结构保存到feature_regs向量中，按照feature索引值由小到大进行排序之后，输出feature索引和名称信息。

    freg = fm->next_feature_by_arc[areg->feature_arc_index];while (freg) {vec_add1 (feature_regs, freg[0]);freg = freg->next_in_arc;}vec_sort_with_function (feature_regs, feature_cmp);vec_foreach (freg, feature_regs) {if (verbose)vlib_cli_output (vm, "  [%2d]: %s\n", freg->feature_index, freg->node_name);elsevlib_cli_output (vm, "  %s\n", freg->node_name);}vec_reset_length (feature_regs);areg = areg->next;}

如下显示：

vpp# show features verbose
Available feature paths
[ 0] nsh-eth-output:[ 0]: interface-output[ 1]: error-drop
[ 1] arp:[ 0]: vrrp4-arp-input[ 1]: linux-cp-arp-phy[ 2]: linux-cp-arp-host[ 3]: arping-input[ 4]: arp-reply[ 5]: arp-proxy[ 6]: arp-disabled[ 7]: error-drop
[ 2] nsh-output:[ 0]: error-drop
[ 3] mpls-input:[ 0]: vlan-mpls-qos-record[ 1]: mpls-qos-record[ 2]: mpls-not-enabled[ 3]: mpls-lookup

接口feature配置

函数vnet_interface_features_show显示在指定接口上激活的feature集合，这里也是由遍历feature_main结构的成员next_arc开头的单链表开始。

void
vnet_interface_features_show (vlib_main_t * vm, u32 sw_if_index, int verbose)
{vnet_feature_main_t *fm = &feature_main;vnet_feature_config_main_t *cm = fm->feature_config_mains;vnet_feature_arc_registration_t *areg;vnet_config_main_t *vcm;vnet_config_t *cfg;vnet_config_feature_t *feat;vlib_node_t *n;vlib_cli_output (vm, "Feature paths configured on %U...",format_vnet_sw_if_index_name, vnet_get_main (), sw_if_index);areg = fm->next_arc;

根据ARC索引找到对应的配置结构vcm，如果接口sw_if_index完全没有激活此ARC，显示"none configured"。否则，检查此接口在此ARC上激活了哪些features。

  while (areg) {feature_arc = areg->feature_arc_index;vcm = &(cm[feature_arc].config_main);vlib_cli_output (vm, "\n%s:", areg->arc_name);areg = areg->next;if (!vnet_have_features (feature_arc, sw_if_index)) {vlib_cli_output (vm, "  none configured");continue;}

先根据sw_if_index接口索引在向量config_index_by_sw_if_index中找到ARC配置索引(current_config_index)，再根据配置索引在向量config_pool_index_by_user_index中找到pool索引，最终，在config_pool中取得相应配置cfg。

遍历cfg结构向量成员features，根据其中的节点索引node_index，找到feature的节点结构。打印输出feature索引和节点名称。

      current_config_index =vec_elt (cm[feature_arc].config_index_by_sw_if_index, sw_if_index);cfg_index =vec_elt (vcm->config_pool_index_by_user_index, current_config_index);cfg = pool_elt_at_index (vcm->config_pool, cfg_index);for (i = 0; i < vec_len (cfg->features); i++) {feat = cfg->features + i;node_index = feat->node_index;n = vlib_get_node (vm, node_index);if (verbose)vlib_cli_output (vm, "  [%2d] %v", feat->feature_index, n->name);elsevlib_cli_output (vm, "  %v", n->name);}

ARC的最后一个节点索引保存在end_node_indices_by_user_index的current_config_index索引位置，vlib_get_node根据最后节点索引找到节点结构，打印其名称。

      if (verbose) {n = vlib_get_node (vm, vcm->end_node_indices_by_user_index[current_config_index]);vlib_cli_output (vm, "  [end] %v", n->name);}

如下显示接口features配置：

vpp# show interface features eth0
Feature paths configured on eth0...nsh-eth-output:none configuredarp:linux-cp-arp-phy

feature开启关闭

feature开启关闭操作需要指定ARC和Feature的名称，以及要开启的接口索引。如下函数，根据ARC和Feature名称找到ARC索引和feature索引。

int
vnet_feature_enable_disable (const char *arc_name, const char *node_name,u32 sw_if_index, int enable_disable,     void *feature_config, u32 n_feature_config_bytes)
{  u32 feature_index;u8 arc_index;arc_index = vnet_get_feature_arc_index (arc_name); if (arc_index == (u8) ~ 0)return VNET_API_ERROR_INVALID_VALUE;feature_index = vnet_get_feature_index (arc_index, node_name);return vnet_feature_enable_disable_with_index (arc_index, feature_index,sw_if_index, enable_disable,             feature_config, n_feature_config_bytes);                 

在feature_main结构中，根据ARC名称，在哈希arc_index_by_name找到ARC的注册结构，其中保存着ARC的索引feature_arc_index。

vnet_get_feature_arc_index (const char *s)
{vnet_feature_main_t *fm = &feature_main;vnet_feature_arc_registration_t *reg;uword *p;p = hash_get_mem (fm->arc_index_by_name, s);if (p == 0)return ~0;reg = uword_to_pointer (p[0], vnet_feature_arc_registration_t *);return reg->feature_arc_index;

在feature_main主结构中，根据ARC索引，和feature名称，在哈希next_feature_by_name[arc]中找到feature的注册结构，其中保存着feature的索引feature_index。

vnet_get_feature_index (u8 arc, const char *s)
{vnet_feature_main_t *fm = &feature_main;vnet_feature_registration_t *reg;uword *p;if (s == 0) return ~0;p = hash_get_mem (fm->next_feature_by_name[arc], s);if (p == 0)return ~0;reg = uword_to_pointer (p[0], vnet_feature_registration_t *);return reg->feature_index;

根据ARC索引找到对应配置结构cm，再根据接口索引sw_if_index在config_index_by_sw_if_index找到配置池索引ci，检查一下接口当前开启的feature数量，如果为零，并且当前为disable操作，直接返回，不需要disable了。

vnet_feature_enable_disable_with_index (u8 arc_index, u32 feature_index,u32 sw_if_index, int enable_disable,void *feature_config, u32 n_feature_config_bytes)
{vnet_feature_main_t *fm = &feature_main;vnet_feature_config_main_t *cm;cm = &fm->feature_config_mains[arc_index];vec_validate_init_empty (cm->config_index_by_sw_if_index, sw_if_index, ~0);ci = cm->config_index_by_sw_if_index[sw_if_index];vec_validate (fm->feature_count_by_sw_if_index[arc_index], sw_if_index);feature_count = fm->feature_count_by_sw_if_index[arc_index][sw_if_index];if (!enable_disable && feature_count < 1)return 0;

调用函数vnet_config_add_feature/vnet_config_del_feature添加或者删除feature。将返回的配置池索引ci保存到接口对应的config_index_by_sw_if_index中。递增接口的feature数量。

ARC对应的向量sw_if_index_has_features[arc_index]中保存接口是否开启有feature。

  ci = (enable_disable? vnet_config_add_feature: vnet_config_del_feature)(vlib_get_main (), &cm->config_main, ci, feature_index, feature_config, n_feature_config_bytes);if (ci == ~0)return 0;cm->config_index_by_sw_if_index[sw_if_index] = ci;/* update feature count */enable_disable = (enable_disable > 0);feature_count += enable_disable ? 1 : -1;ASSERT (feature_count >= 0);fm->sw_if_index_has_features[arc_index] =clib_bitmap_set (fm->sw_if_index_has_features[arc_index], sw_if_index, (feature_count > 0));fm->feature_count_by_sw_if_index[arc_index][sw_if_index] = feature_count;vnet_feature_reg_invoke (sw_if_index, arc_index, (feature_count > 0));

如下增加feature函数，如果config_string_heap_index为有效值，据此获得之前添加的vnet_config_t结构old（这里将p进行了减一操作，之后会再次看着这个值进行了加一保存），将其中的features复制一份。

vnet_config_add_feature (vlib_main_t * vm,vnet_config_main_t * cm, u32 config_string_heap_index,u32 feature_index, void *feature_config, u32 n_feature_config_bytes)
{vnet_config_t *old, *new;vnet_config_feature_t *new_features, *f;u32 n_feature_config_u32s, end_node_index;u32 node_index = vec_elt (cm->node_index_by_feature_index, feature_index);if (config_string_heap_index == ~0) {old = 0;new_features = 0;end_node_index = cm->default_end_node_index;} else {u32 *p = vnet_get_config_heap (cm, config_string_heap_index);old = pool_elt_at_index (cm->config_pool, p[-1]);new_features = old->features;end_node_index = cm->end_node_indices_by_user_index[config_string_heap_index];if (new_features)new_features = duplicate_feature_vector (new_features);}

分配一个新的feature结构vnet_config_feature_t，将要添加的feature索引和节点索引赋值到新feature结构中。如果指定了配置字节，保存到新feature结构中。

  vec_add2 (new_features, f, 1);f->feature_index = feature_index;f->node_index = node_index;if (n_feature_config_bytes) {n_feature_config_u32s = round_pow2 (n_feature_config_bytes, sizeof (f->feature_config[0])) / sizeof (f->feature_config[0]);vec_validate (f->feature_config, n_feature_config_u32s - 1);clib_memcpy_fast (f->feature_config, feature_config, n_feature_config_bytes);}

如果new_features向量元素大于1，进行排序。释放旧的vnet_config结构。函数find_config_with_features分配一个新的vnet_config结构new。

  /* Sort (prioritize) features. */if (vec_len (new_features) > 1)vec_sort_with_function (new_features, feature_cmp);if (old)remove_reference (cm, old);new = find_config_with_features (vm, cm, new_features, end_node_index);new->reference_count += 1;

分配config_pool_index_by_user_index索引，将配置池索引进行保存。返回配置池索引值（进行了加一操作）。

  /* User gets pointer to config string first element* (which defines the pool index this config string comes from).*/vec_validate (cm->config_pool_index_by_user_index,new->config_string_heap_index + 1);cm->config_pool_index_by_user_index[new->config_string_heap_index + 1]= new - cm->config_pool;return new->config_string_heap_index + 1;