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以前看内核代码觉得难#xff0c;是因为内核代码涉及到硬件原理与算法结构和层次递进的代码逻辑#xff0c;现在的应用层因为业务的复杂与代码和内核的交互接口复杂#xff0c;也变得有些难度了。
这篇文章是继:openbmc dbus架构简析的第二篇文章。
首先贴出来前篇…1.说明
以前看内核代码觉得难是因为内核代码涉及到硬件原理与算法结构和层次递进的代码逻辑现在的应用层因为业务的复杂与代码和内核的交互接口复杂也变得有些难度了。
这篇文章是继:openbmc dbus架构简析的第二篇文章。
首先贴出来前篇文章的图与简述内容:
* 1.inherit_fds()使用systemd机制获取到socket描述符(请先了解systemd的socket机制原理会先接手socket服务accept默认为no,因此需要sd_listen_fds()方法获取socket描述符)
* 2.父子进程通过socketpair(PF_UNIX, SOCK_STREAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0, controller);中的controller[0]和controller[1]进行连接
* 3.sd_bus_set_fd(launcher-bus_controller, controller[0], controller[0]);使用该函数,实际bus-input_fd input_fd;bus-output_fd output_fd; 实际即为controller[0]
* 4.sd_bus_call(launcher-bus_controller, m, 0, NULL, NULL);发送socket数据实际依靠的是controller[0],而子进程使用的是controller[1],通道打通数据可以传递给子进程
* 5.sd_bus_message_append(m, oh,/org/bus1/DBus/Listener/0,launcher-fd_listen);把launcher-fd_listen 为总体的systemd的监听的socket描述符传递给了子进程。2.代码分析
2.1 代码使用的描述符
2.1.1 dbus-broker-launch使用的描述符
根据代码列出来使用到的描述符:
static int run(void)
--- launcher_new()--- r launcher_open_log(launcher);--- fd socket(PF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0); //新建了描述符 fd4--- sd_event_default(launcher-event);---...--- e-epoll_fd epoll_create1(EPOLL_CLOEXEC); //创建了描述 epoll_fd5.--- r sd_event_add_signal(launcher-event, NULL, SIGTERM, NULL, NULL);--- r sd_event_add_signal(launcher-event, NULL, SIGTERM, NULL, NULL);--- r sd_event_add_signal(launcher-event, NULL, SIGTERM, NULL, NULL);--- r event_make_signal_data(e, sig, d);--- r signalfd(d-fd 0 ? d-fd : -1,...) 使用了signalfd创建的fd6
--- r launcher_run(launcher);--- r launcher_parse_config(launcher, root, nss_cache);--- r dirwatch_new(dirwatch); --- dw-inotify_fd inotify_init1(IN_CLOEXEC | IN_NONBLOCK); //新建fd7--- r config_parser_read(parser, rootp, configfile, nss_cache, dirwatch);--- r config_parser_include(parser, root, node, nss_cache, dirwatch);--- _c_cleanup_(c_closep) int fd -1;--- r open(node-include.file-path, O_RDONLY | O_CLOEXEC | O_NOCTTY);--- ... //这里 fd8, 实际需要调用close() 使用_c_cleanup_语法实际关闭了--- r socketpair(PF_UNIX, SOCK_STREAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0, controller);--- ...返回了2个套接字 分别为 controller[0] 8 和 controller[0] 9如下图可以看到基本的文件描述符均为默认状态: 参考文档: https://www.jinbuguo.com/systemd/systemd.exec.html# 描述了如下内容: 因此fd0,fd1,fd2的结果如下: 因此对于openbmc常见的printf,fprintf(stderr…)均会输出到journal中。
对于fd3继承于systemd接收外部的服务。对于fd4创建socket用来将数据传递到:/run/systemd/journal/socket对于fd5, 创建e-epoll_fd对于fd6,使用signalfd()创建fd对于fd7,使用inotify_init1()创建fd对于fd8,fd9使用socketpair()创建fd用来父子进程数据通信
再回到开头的那副图可以看看子进程与父进程之间父进程通过sd-bus接口调用将fd(systemd监控转储给dbus-broker的socket)描述符传递给子进程。 继续分析文件:src\launch\launcher.c:
static int launcher_add_listener(Launcher *launcher, Policy *policy,...)
--- r sd_bus_message_new_method_call(launcher-bus_controller, m,NULL,/org/bus1/DBus/Broker,org.bus1.DBus.Broker,AddListener);--- _cleanup_(sd_bus_message_unrefp) sd_bus_message *t NULL;--- r sd_bus_message_new(bus, t, SD_BUS_MESSAGE_METHOD_CALL);--- t-header-endian BUS_NATIVE_ENDIAN;--- t-header-type type;--- t-header-version bus-message_version;--- t-allow_fds bus-can_fds || !IN_SET(bus-state, BUS_HELLO, BUS_RUNNING);
--- r sd_bus_message_append(m, oh,/org/bus1/DBus/Listener/0,launcher-fd_listen);
--- r policy_export(policy, m, system_console_users, n_system_console_users);
--- r sd_bus_call(launcher-bus_controller, m, 0, NULL, NULL);实际上这里面的重点是函数:sd_bus_call(),在文件:src\libsystemd\sd-bus\sd-bus.c中:
int sd_bus_call(...)
--- bus_write_message()--- bus_socket_write_message()--- if (m-n_fds 0 *idx 0)--- mh.msg_controllen CMSG_SPACE(sizeof(int) * m-n_fds);--- mh.msg_control alloca0(mh.msg_controllen);--- control CMSG_FIRSTHDR(mh);--- control-cmsg_len CMSG_LEN(sizeof(int) * m-n_fds);--- control-cmsg_level SOL_SOCKET;--- control-cmsg_type SCM_RIGHTS;--- memcpy(CMSG_DATA(control), m-fds, sizeof(int) * m-n_fds);--- k sendmsg(bus-output_fd, mh, MSG_DONTWAIT|MSG_NOSIGNAL);使用如上调用步骤传递文件描述符给另外一个进程使用的方法是父子进程之间通过sendmsg()调用。
继续查看函数sd_bus_message_append()的调用关系:
int sd_bus_message_append(sd_bus_message *m, const char *types, ...)
--- r sd_bus_message_appendv(m, types, ap); //type是字符串oh
--- switch (*t)--- case SD_BUS_TYPE_UNIX_FD:--- uint32_t x;--- x va_arg(ap, uint32_t);--- r sd_bus_message_append_basic(m, *t, x);--- u32 m-n_fds;--- case SD_BUS_TYPE_OBJECT_PATH:--- const char *x;--- x va_arg(ap, const char*);--- r sd_bus_message_append_basic(m, *t, x);这些sd-bus类型有必要列出来在文件:src\systemd\sd-bus-protocol.h中:
enum {_SD_BUS_TYPE_INVALID 0,SD_BUS_TYPE_BYTE y,SD_BUS_TYPE_BOOLEAN b,SD_BUS_TYPE_INT16 n,SD_BUS_TYPE_UINT16 q,SD_BUS_TYPE_INT32 i,SD_BUS_TYPE_UINT32 u,SD_BUS_TYPE_INT64 x,SD_BUS_TYPE_UINT64 t,SD_BUS_TYPE_DOUBLE d,SD_BUS_TYPE_STRING s,SD_BUS_TYPE_OBJECT_PATH o,SD_BUS_TYPE_SIGNATURE g,SD_BUS_TYPE_UNIX_FD h,SD_BUS_TYPE_ARRAY a,SD_BUS_TYPE_VARIANT v,SD_BUS_TYPE_STRUCT r, /* not actually used in signatures */SD_BUS_TYPE_STRUCT_BEGIN (,SD_BUS_TYPE_STRUCT_END ),SD_BUS_TYPE_DICT_ENTRY e, /* not actually used in signatures */SD_BUS_TYPE_DICT_ENTRY_BEGIN {,SD_BUS_TYPE_DICT_ENTRY_END }
};在文件:src\broker\controller.c中函数:controller_init()调用:
int controller_init(Controller *c, Broker *broker, int controller_fd)
--- r connection_init_server(controller-connection,broker-dispatcher,controller_dispatch_connection,broker-bus.user,0123456789abcdef,controller_fd);其中函数controller_dispatch_connection()定义:
static int controller_dispatch_connection(DispatchFile *file)
--- r connection_dispatch(controller-connection, dispatch_file_events(file));
--- r connection_dequeue(controller-connection, m);--- r socket_dequeue(connection-socket, message);--- r message_new_incoming(message, socket-in.header);
--- r message_parse_metadata(m);--- r message_parse_header(message, message-metadata);--- switch (field)--- case DBUS_MESSAGE_FIELD_PATH:--- case DBUS_MESSAGE_FIELD_INTERFACE:--- case DBUS_MESSAGE_FIELD_MEMBER:--- case DBUS_MESSAGE_FIELD_REPLY_SERIAL:--- case DBUS_MESSAGE_FIELD_UNIX_FDS:--- c_dvar_read(v, u), c_dvar_type_u, metadata-fields.unix_fds);--- r message_parse_body(message, message-metadata);
--- r controller_dbus_dispatch(controller, m);--- switch (message-header-type) {--- case DBUS_MESSAGE_TYPE_METHOD_CALL:--- r controller_dispatch_object(controller,message_read_serial(message),message-metadata.fields.interface,message-metadata.fields.member,message-metadata.fields.path,message-metadata.fields.signature,message);--- if (strcmp(path, /org/bus1/DBus/Broker) 0)--- controller_dispatch_controller(controller, serial, member, path, signature, message);--- controller_method_add_listener( ... )--- listener_fd fdlist_get(fds, fd_index);--- r controller_add_listener(controller, listener, path, listener_fd, policy);--- listener_init_with_fd(...)--- listener-bus bus;--- dispatch_file_init(.., listener_dispatch,... ) 这里面的判断:message-header-type来自于src\launch\launcher.c的sd_bus_message_new_method_call( )
最后调用到函数listener_dispatch():
static int listener_dispatch(DispatchFile *file)
--- fd accept4(listener-socket_fd, NULL, NULL, SOCK_CLOEXEC | SOCK_NONBLOCK);2.1.2 socket takeover
需要首先查阅该篇文章: Zero Downtime Release: Disruption-free Load Balancing of a Multi-Billion User Website.
可参考文件src\util\log.c中的函数log_fd_send():
static int log_fd_send(int destination_fd, int payload_fd)
--- control.cmsg.cmsg_level SOL_SOCKET;
--- control.cmsg.cmsg_type SCM_RIGHTS;
--- l sendmsg(destination_fd, msg, MSG_NOSIGNAL);2.1.3 描述符附录
简单看一下应用程序使用的描述符: rootevb-ast2500:~# ps | grep -i dbus191 messageb 5836 S /usr/bin/dbus-broker-launch --scope system --audit192 messageb 2756 S dbus-broker --log 4 --controller 9 --machine-id c47c0d3d042848a1908818ca62f0644e --max-bytes 536870912 --max-fds 4096 --max-matches 16384 --audit344 root 2952 S grep -i dbus
rootevb-ast2500:~#
rootevb-ast2500:~# ls -al /proc/191/fd
dr-x------ 2 root root 13 Feb 27 17:54 .
dr-xr-xr-x 8 messageb messageb 0 Feb 27 17:54 ..
lr-x------ 1 root root 64 Feb 27 17:54 0 - /dev/null
lrwx------ 1 root root 64 Feb 27 17:54 1 - socket:[2242]
lrwx------ 1 root root 64 Feb 27 17:55 10 - anon_inode:[pidfd]
lrwx------ 1 root root 64 Feb 27 17:55 11 - anon_inode:[timerfd]
lrwx------ 1 root root 64 Feb 27 17:55 12 - /memfd:dbus-broker-log (deleted)
lrwx------ 1 root root 64 Feb 27 17:54 2 - socket:[2242]
lrwx------ 1 root root 64 Feb 27 17:54 3 - socket:[2210]
lrwx------ 1 root root 64 Feb 27 17:54 4 - socket:[2246]
lrwx------ 1 root root 64 Feb 27 17:55 5 - anon_inode:[eventpoll]
lrwx------ 1 root root 64 Feb 27 17:55 6 - anon_inode:[signalfd]
lr-x------ 1 root root 64 Feb 27 17:55 7 - anon_inode:inotify
lrwx------ 1 root root 64 Feb 27 17:55 8 - socket:[2254]
lrwx------ 1 root root 64 Feb 27 17:54 9 - socket:[2303]
rootevb-ast2500:~#2.2 bus的建立
2.2.1 launcher bus
在文件:src\launch\launcher.c中调用如下函数launcher_new():
int launcher_new(Launcher **launcherp, int fd_listen, bool audit, const char *configfile, bool user_scope)
--- r sd_bus_new(launcher-bus_controller);另外函数:launcher_run()调用如下:
int launcher_run(Launcher *launcher)
--- r sd_bus_set_fd(launcher-bus_controller, controller[0], controller[0]);
--- r sd_bus_start(launcher-bus_controller);--- bus_set_state(bus, BUS_OPENING);--- if (bus-input_fd 0) --- r bus_start_fd(bus);--- return bus_send_hello(bus);//直接返回并未调用hello由于开启的服务是:
在函数:launcher_connect()中:
static int launcher_connect(Launcher *launcher)
--- r sd_bus_open_system(launcher-bus_regular);--- sd_bus_open_system_with_description(ret, NULL);--- r sd_bus_new(b);--- r bus_set_address_system(b);--- b-bus_client true;--- b-is_local true;--- r sd_bus_start(b);--- bus_set_state(bus, BUS_OPENING);--- r bus_start_address(bus);--- return bus_send_hello(bus);--- r sd_bus_message_new_method_call(bus, m,org.freedesktop.DBus,/org/freedesktop/DBus,org.freedesktop.DBus,Hello);--- sd_bus_call_async(bus, NULL, m, hello_callback, NULL, 0);设置系统默认的bus:unix:path/run/dbus/system_bus_socket. 在如下调用关系中:
static int listener_dispatch(DispatchFile *file)
--- ...
--- r peer_dispatch(peer-connection.socket_file);--- r peer_dispatch_connection(peer, dispatch_file_events(file) interest[i]);--- r connection_dispatch(peer-connection, events);--- r connection_dequeue(peer-connection, m);--- r message_parse_metadata(m);--- r driver_dispatch(peer, m);--- r driver_dispatch_internal(peer, message);--- if (string_equal(message-metadata.fields.destination, org.freedesktop.DBus))--- driver_dispatch_interface(peer,...) --- static const DriverInterface interfaces[] {--- { org.freedesktop.DBus, driver_methods },--- { org.freedesktop.DBus.Monitoring, monitoring_methods },--- ... --- }其中函数:driver_methods():
static const DriverMethod driver_methods[] {{ Hello, false, NULL, driver_method_hello, ...}static int driver_method_hello(Peer *peer, const char *path, CDVar *in_v, uint32_t serial, CDVar *out_v)
--- peer_register(peer);--- peer-registered true;
--- unique_name address_to_string((Address)ADDRESS_INIT_ID(peer-id)); //获取unique name
--- c_dvar_write(out_v, (s), unique_name); //将unique name返回
--- r driver_send_reply(peer, out_v, serial);--- driver_send_reply_with_fds(peer, var, serial, NULL, 0);--- r message_new_outgoing(message, data, n_data);--- r driver_send_unicast(peer, message);
--- r driver_name_owner_changed(peer-bus, peer-name_owner_changed_matches, NULL, NULL, peer);--- r driver_notify_name_owner_changed(bus, matches, name, old_owner_str, new_owner_str);--- .fields {--- .path /org/freedesktop/DBus,--- .interface org.freedesktop.DBus,--- .member NameOwnerChanged,--- }3.分析一下权威代码
3.1 LogControl
可以查看网站:https://www.freedesktop.org/software/systemd/man/latest/org.freedesktop.LogControl1.html 或者systemd的代码: man\logcontrol-example.c.
注意:此处是建立一个server
int main(int argc, char **argv)
--- r sd_bus_default(bus);--- b-bus_client true;
--- r sd_bus_add_object_vtable(bus, NULL,/org/freedesktop/LogControl1,org.freedesktop.LogControl1,vtable,o);
--- r sd_bus_request_name(bus, org.freedesktop.Example, 0);--- r sd_bus_call_method(bus,org.freedesktop.DBus,/org/freedesktop/DBus,org.freedesktop.DBus,RequestName,NULL,reply,su,name,param);--- r sd_bus_message_read(reply, u, ret);
--- for()--- {--- r sd_bus_wait(bus, UINT64_MAX);--- r bus_poll(bus, false, timeout_usec);--- r sd_bus_process(bus, NULL);--- bus_process_internal(bus, ret);--- }另外systemd的代码:src\busctl\busctl.c是客户端代码查看如下命令: * $ busctl --user set-property org.freedesktop.Example \* /org/freedesktop/LogControl1 \* org.freedesktop.LogControl1 \* LogLevel \* s debug代码调用如下:
static int run(int argc, char *argv[])
--- busctl_main(argc, argv);--- r acquire_bus(false, bus);--- r sd_bus_new(bus);--- sd_bus_set_description(bus, busctl);--- r sd_bus_set_bus_client(bus, true);bus-bus_client b;--- r sd_bus_set_watch_bind(bus, arg_watch_bind);--- r sd_bus_start(bus);--- bus_send_hello(bus);--- r sd_bus_message_new_method_call(bus, m, argv[1], argv[2],org.freedesktop.DBus.Properties, Set);--- r sd_bus_message_append(m, ss, argv[3], argv[4]);--- r sd_bus_message_open_container(m, v, argv[5]);--- r message_append_cmdline(m, argv[5], passed_fdset, p);--- r sd_bus_message_close_container(m);--- r sd_bus_call(bus, m, arg_timeout, error, NULL);4.TBD…
