static int ieee80211_vif_update_links(struct ieee80211_sub_if_data *sdata,
struct link_container **to_free,
u16 new_links, u16 dormant_links)
{
u16 old_links = sdata->vif.valid_links;
u16 old_active = sdata->vif.active_links;
unsigned long add = new_links & ~old_links;
unsigned long rem = old_links & ~new_links;
unsigned int link_id;
int ret;
struct link_container *links[IEEE80211_MLD_MAX_NUM_LINKS] = {}, *link;
struct ieee80211_bss_conf *old[IEEE80211_MLD_MAX_NUM_LINKS];
struct ieee80211_link_data *old_data[IEEE80211_MLD_MAX_NUM_LINKS];
bool use_deflink = old_links == 0; /* set for error case */
lockdep_assert_wiphy(sdata->local->hw.wiphy);
memset(to_free, 0, sizeof(links));
if (old_links == new_links && dormant_links == sdata->vif.dormant_links)
return 0;
/* if there were no old links, need to clear the pointers to deflink */
if (!old_links)
rem |= BIT(0);
/* allocate new link structures first */
for_each_set_bit(link_id, &add, IEEE80211_MLD_MAX_NUM_LINKS) {
link = kzalloc(sizeof(*link), GFP_KERNEL);
if (!link) {
ret = -ENOMEM;
goto free;
}
links[link_id] = link;
}
/* keep track of the old pointers for the driver */
BUILD_BUG_ON(sizeof(old) != sizeof(sdata->vif.link_conf));
memcpy(old, sdata->vif.link_conf, sizeof(old));
/* and for us in error cases */
BUILD_BUG_ON(sizeof(old_data) != sizeof(sdata->link));
memcpy(old_data, sdata->link, sizeof(old_data));
/* grab old links to free later */
for_each_set_bit(link_id, &rem, IEEE80211_MLD_MAX_NUM_LINKS) {
if (rcu_access_pointer(sdata->link[link_id]) != &sdata->deflink) {
/*
* we must have allocated the data through this path so
* we know we can free both at the same time
*/
to_free[link_id] = container_of(rcu_access_pointer(sdata->link[link_id]),
typeof(*links[link_id]),
data);
}
RCU_INIT_POINTER(sdata->link[link_id], NULL);
RCU_INIT_POINTER(sdata->vif.link_conf[link_id], NULL);
}
if (!old_links)
ieee80211_debugfs_recreate_netdev(sdata, true);
/* link them into data structures */
for_each_set_bit(link_id, &add, IEEE80211_MLD_MAX_NUM_LINKS) {
WARN_ON(!use_deflink &&
rcu_access_pointer(sdata->link[link_id]) == &sdata->deflink);
link = links[link_id];
ieee80211_link_init(sdata, link_id, &link->data, &link->conf);
ieee80211_link_setup(&link->data);
if (sdata->vif.type != NL80211_IFTYPE_AP_VLAN)
ieee80211_set_wmm_default(&link->data, true,
sdata->vif.type != NL80211_IFTYPE_STATION);
}
if (new_links == 0)
ieee80211_link_init(sdata, -1, &sdata->deflink,
&sdata->vif.bss_conf);
ret = ieee80211_check_dup_link_addrs(sdata);
if (!ret) {
ieee80211_debugfs_remove_link(sdata, rem);
/* for keys we will not be able to undo this */
ieee80211_tear_down_links(sdata, to_free, rem);
ieee80211_set_vif_links_bitmaps(sdata, new_links, dormant_links);
ieee80211_debugfs_add_link(sdata, add);
/* tell the driver */
if (sdata->vif.type != NL80211_IFTYPE_AP_VLAN)
ret = drv_change_vif_links(sdata->local, sdata,
old_links & old_active,
new_links & sdata->vif.active_links,
old);
if (!new_links)
ieee80211_debugfs_recreate_netdev(sdata, false);
if (sdata->vif.type == NL80211_IFTYPE_AP)
ieee80211_update_apvlan_links(sdata);
}
if (ret) {
/* restore config */
memcpy(sdata->link, old_data, sizeof(old_data));
memcpy(sdata->vif.link_conf, old, sizeof(old));
ieee80211_set_vif_links_bitmaps(sdata, old_links, dormant_links);
/* and free (only) the newly allocated links */
memset(to_free, 0, sizeof(links));
goto free;
}
/* use deflink/bss_conf again if and only if there are no more links */
use_deflink = new_links == 0;
goto deinit;
free:
/* if we failed during allocation, only free all */
for (link_id = 0; link_id < IEEE80211_MLD_MAX_NUM_LINKS; link_id++) {
kfree(links[link_id]);
links[link_id] = NULL;
}
deinit:
if (use_deflink)
ieee80211_link_init(sdata, -1, &sdata->deflink,
&sdata->vif.bss_conf);
return ret;
} 可以不用deflink吗
本文介绍了一个特殊的宏定义BUILD_BUG_ON，该宏在条件为真时会强制触发一个编译时错误。通过使用sizeof和类型不匹配的技巧来实现这一目标。
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