DRBD源码分析(二)——内核模块网络配置和启动

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在上一篇里面分析到了基于netlink的connector,connector正是内核态与用户态配置命令交互的通道。用户通过调用用户态的工具,发送相应的命令参数,用户态工具将命令参数转换成相应的消息包,内核态解析消息后得到相应的指令,继续转换成函数调用,最后得以执行。

首先仔细看一下上一节提到的创建connector时注册的收数据的回调函数:

#ifdef KERNEL_HAS_CN_SKB_PARMS
STATIC void drbd_connector_callback(struct cn_msg *req, struct netlink_skb_parms *nsp)
{
#else
STATIC void drbd_connector_callback(void *data)
{
struct cn_msg *req = data;
#endif
struct drbd_nl_cfg_req *nlp = (struct drbd_nl_cfg_req *)req->data;
struct cn_handler_struct *cm;
struct cn_msg *cn_reply;
struct drbd_nl_cfg_reply *reply;
struct drbd_conf *mdev;
int retcode, rr;
int reply_size = sizeof(struct cn_msg)
+ sizeof(struct drbd_nl_cfg_reply)
+ sizeof(short int);

if (!try_module_get(THIS_MODULE)) {
printk(KERN_ERR "drbd: try_module_get() failed!\n");
return;
}

#ifdef KERNEL_HAS_CN_SKB_PARMS
if (!cap_raised(nsp->eff_cap, CAP_SYS_ADMIN)) {
retcode = ERR_PERM;
goto fail;
}
#endif

mdev = ensure_mdev(nlp);
if (!mdev) {
retcode = ERR_MINOR_INVALID;
goto fail;
}

trace_drbd_netlink(req, 1);

if (nlp->packet_type >= P_nl_after_last_packet) {
retcode = ERR_PACKET_NR;
goto fail;
}
printk("packet_type is %d\n", nlp->packet_type);
cm = cnd_table + nlp->packet_type;

/* This may happen if packet number is 0: */
if (cm->function == NULL) {
retcode = ERR_PACKET_NR;
goto fail;
}

reply_size += cm->reply_body_size;

/* allocation not in the IO path, cqueue thread context */
cn_reply = kmalloc(reply_size, GFP_KERNEL);
if (!cn_reply) {
retcode = ERR_NOMEM;
goto fail;
}
reply = (struct drbd_nl_cfg_reply *) cn_reply->data;

reply->packet_type =
cm->reply_body_size ? nlp->packet_type : P_nl_after_last_packet;
reply->minor = nlp->drbd_minor;
reply->ret_code = NO_ERROR; /* Might by modified by cm->function. */
/* reply->tag_list; might be modified by cm->function. */

rr = cm->function(mdev, nlp, reply);

cn_reply->id = req->id;
cn_reply->seq = req->seq;
cn_reply->ack = req->ack + 1;
cn_reply->len = sizeof(struct drbd_nl_cfg_reply) + rr;
cn_reply->flags = 0;

trace_drbd_netlink(cn_reply, 0);
rr = cn_netlink_send(cn_reply, CN_IDX_DRBD, GFP_KERNEL);
if (rr && rr != -ESRCH)
printk(KERN_INFO "drbd: cn_netlink_send()=%d\n", rr);

kfree(cn_reply);
module_put(THIS_MODULE);
return;
fail:
drbd_nl_send_reply(req, retcode);
module_put(THIS_MODULE);
}

值得注意的是:

rr=cm->function(mdev,nlp,reply);

这一句,这里相当于是一个多态,function绑定到哪一个方法由消息包中携带的包类型决定:


cm=cnd_table+nlp->packet_type;

系统在初始化时级生成了一个全局的静态函数表,类似P_primary的标识符是在编译时动态生成的宏。表示其所在的元素的下标,同时也月包类型相对应。

static struct cn_handler_struct cnd_table[] = {
[ P_primary ] = { &drbd_nl_primary, 0 },
[ P_secondary ] = { &drbd_nl_secondary, 0 },
[ P_disk_conf ] = { &drbd_nl_disk_conf, 0 },
[ P_detach ] = { &drbd_nl_detach, 0 },
[ P_net_conf ] = { &drbd_nl_net_conf, 0 },
[ P_disconnect ] = { &drbd_nl_disconnect, 0 },
[ P_resize ] = { &drbd_nl_resize, 0 },
[ P_syncer_conf ] = { &drbd_nl_syncer_conf, 0 },
[ P_invalidate ] = { &drbd_nl_invalidate, 0 },
[ P_invalidate_peer ] = { &drbd_nl_invalidate_peer, 0 },
[ P_pause_sync ] = { &drbd_nl_pause_sync, 0 },
[ P_resume_sync ] = { &drbd_nl_resume_sync, 0 },
[ P_suspend_io ] = { &drbd_nl_suspend_io, 0 },
[ P_resume_io ] = { &drbd_nl_resume_io, 0 },
[ P_outdate ] = { &drbd_nl_outdate, 0 },
[ P_get_config ] = { &drbd_nl_get_config,
sizeof(struct syncer_conf_tag_len_struct) +
sizeof(struct disk_conf_tag_len_struct) +
sizeof(struct net_conf_tag_len_struct) },
[ P_get_state ] = { &drbd_nl_get_state,
sizeof(struct get_state_tag_len_struct) +
sizeof(struct sync_progress_tag_len_struct) },
[ P_get_uuids ] = { &drbd_nl_get_uuids,
sizeof(struct get_uuids_tag_len_struct) },
[ P_get_timeout_flag ] = { &drbd_nl_get_timeout_flag,
sizeof(struct get_timeout_flag_tag_len_struct)},
[ P_start_ov ] = { &drbd_nl_start_ov, 0 },
[ P_new_c_uuid ] = { &drbd_nl_new_c_uuid, 0 },
};

比如,在一次完整的用户态与内核态的交互中,用户态会多次发出P_get_state消息,该消息的包类型码为17。

类似cn_handler_struct这样的函数表,在drbd的代码中随处可见,无论是内核态还是用户态,这样一致的风格,应该非常利于扩展和维护。看代码的人也会觉得非常轻松,不至于无章可循。

DRBD的配置信息、虚拟设备、网络通信端口、对端信息等都是通过drbdsetup或者drbdadm工具以netlink消息包发送到内核态的。

在收到5号消息包时,drbd_nl_net_conf会被调用。在该函数中,会启动worker内核线程,该线程监控一个等待队列,当有事件到来时,即取出处理:

int drbd_worker(struct drbd_thread* thi)
{
...
w = NULL;
spin_lock_irq(&mdev->data.work.q_lock);
ERR_IF(list_empty(&mdev->data.work.q))
{
/* something terribly wrong in our logic.
* we were able to down() the semaphore,
* but the list is empty... doh.
*
* what is the best thing to do now?
* try again from scratch, restarting the receiver,
* asender, whatnot? could break even more ugly,
* e.g. when we are primary, but no good local data.
*
* I'll try to get away just starting over this loop.
*/
spin_unlock_irq(&mdev->data.work.q_lock);
continue;
}
w = list_entry(mdev->data.work.q.next, struct drbd_work, list);
list_del_init(&w->list);
spin_unlock_irq(&mdev->data.work.q_lock);

if (!w->cb(mdev, w, mdev->state.conn < C_CONNECTED))
{
/* dev_warn(DEV, "worker: a callback failed! \n"); */
if (mdev->state.conn >= C_CONNECTED)
drbd_force_state(mdev, NS(conn, C_NETWORK_FAILURE));
}
...
}

启动了worker线程之后,几乎所有的内核态的事务都会交给这个线程来处理。

继续回到drbd_nl_net_conf方法中,在初始化完worker线程后,会继续执行如下语句:

retcode=_drbd_request_state(mdev,NS(conn,C_UNCONNECTED),CS_VERBOSE);

这里既是与对端协商确定当前谁是主节点。在该方法中会向等待队列中放入一个事务,该事务为启动一个receiver线程,receiver线程会使用配置文件中指定的端口和IP信息建立tcp socket监听,等待对端的链接。此时,如果对端一直未有连接过来,本端尝试与对端连接也一直无法建立,则会根据配置等待指定的超时时间,之后会将本段置为Standalone状态。这也就是我们常见的两台服务器同时重启时,会发现一端的启动过程卡在drbd的等待上面。

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| 1 分2 分3 分4 分5 分 (4.83- 6票)
Loading ... Loading ... | 这篇文章归档在:C/C++, DRBD
| 标签: . | 永久链接:链接 | 评论(3) |

3 条评论

  1. nlqlove
    评论于 八月 18, 2013 at 14:27:37 CST | 评论链接

    好像还是能被机器人攻入 

    • 评论于 八月 18, 2013 at 22:11:32 CST | 评论链接

      好像还是搞不定,感觉是人工的,不可能是机器人了。

    • 评论于 八月 18, 2013 at 22:17:22 CST | 评论链接

      反垃圾是一项长期而艰巨的任务,哈哈。

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