Dalam rilis baru systemd v221, kami memperkenalkan sd-bus API yang disertakan dengan rilis stabil systemd . sd-bus adalah library D-Bus IPC C minimal kami , mendukung D-Bus berbasis soket klasik dan kdbus sebagai backend . Pustaka telah menjadi bagian dari systemd untuk beberapa waktu, tetapi itu hanya digunakan secara internal karena kami ingin dengan bebas membuat perubahan pada API tanpa mempengaruhi pengguna eksternal. Namun, sekarang, dimulai dengan v221, kami yakin telah membuat API yang stabil.
Dalam posting ini, saya memberikan gambaran umum tentang perpustakaan sd-bus, rekap singkat tentang dasar-dasar D-Bus dan konsepnya, dan beberapa contoh sederhana tentang cara menulis klien dan layanan D-Bus yang menggunakannya.
Apa itu D-Bus?
Mari kita mulai dengan pengingat singkat tentang apa sebenarnya D-Bus itu. Ini adalah sistem IPC tujuan umum yang kuat untuk Linux dan sistem operasi lain. Ini mendefinisikan konsep seperti bus, objek, antarmuka, metode, sinyal, properti. Ini memberi Anda kontrol akses granular, sistem tipe kaya, penemuan mudah, diagnostik mandiri, pemantauan, multicasting andal, startup layanan, transfer deskriptor file, dan banyak lagi. Ada banyak binding untuk bahasa pemrograman yang digunakan di Linux.
D-Bus telah menjadi komponen inti sistem Linux selama lebih dari 10 tahun. Sejauh ini, ini adalah sistem IPC lokal tingkat tinggi yang paling banyak digunakan di Linux. Sejak awal, systemd telah menjadi sistem IPC di mana ia mengekspos antarmukanya. Dan bahkan sebelum systemd, itu adalah sistem IPC yang digunakan Upstart untuk antarmukanya. Ini digunakan oleh GNOME, KDE dan banyak komponen sistem.
D-Bus , . , . , , , - , . ( kdbus .)
D-Bus IPC AF_UNIX. TCP/IP. , D-Bus TCP . D-Bus , ssh, . systemd , API .
D-Bus: , , AF_UNIX FIFO UNIX . , D-Bus -: AF_UNIX/FIFO D-Bus , TCP HTTP/REST. , AF_UNIX/FIFO , D-Bus , , , , .
10- D-Bus , , , - ( , kdbus, sd-bus), , , . IPC, , D-Bus, , , D-Bus.
: D-Bus . Linux IPC, . , D-Bus , , , .
sd-bus?
, sd-bus, D-Bus .
D-Bus: libdbus, D-Bus, GDBus, GLib, GNOME.
libdbus , . , . , API , API , . , , . , (, OOM , ) , Windows UNIX.
GDBus - . GLib/GObject libdbus. GDBus , libdbus. libdbus, , GObject D-Bus GObject. D-Bus GVariant, GLib. GLib, , D-Bus , libdbus.
sd-bus , libdbus, GDBus. libdbus GDBus: , , , , , , , GDBus/GLib/GObject/GVariant. systemd, OOM. , , kdbus D-Bus («dbus1»). , kdbus, dbus1, - , . libdbus GDBus, sd-bus, Linux Linux , . , ( ): libdbus, GDBus . ( ), . , : , kdbus , , , libdbus GDBus.
, , API :
GLib/GObject, GDBus .
, Linux, Windows, Mac OS UNIX, GDBus ( GLib/GObject), libdbus ( ).
sd-bus.
( C++, . : Qt, QtDBus API D-Bus, libdbus.)
D-Bus
D-Bus . , . . :
- , IPC. : , , ; , , , . ( , , , , , , , .)
- , IPC API . . ,
org.freedesktop.NetworkManager
- , API- NetworkManager,org.freedesktop.login1
- , API-systemd-logind
.
- , IPC API . , , , . , . .
- . , , - . - , , . , D-Bus , , . :
/org/freedesktop/login1
- «»org.freedesktop.login1
(, , systemd-logind). , . , ,systemd-logind
/org/freedesktop/login1/session
, :/org/freedesktop/login1/session/_7
,/org/freedesktop/login1/session./_55
. , .
, , . - , ( ), . D-Bus , , Java, . , . , . (, , , , .) , , , . ,
org.freedesktop.DBus.Introspectable
,org.freedesktop.DBus.Peer
org.freedesktop.DBus.Properties
.
. «» «», - , Java. D-Bus , . D-Bus . , , . ( ) CamelCase. ,
systemd-logind
ActivateSession
org.freedesktop.login1.Manager
,/org/freedesktop/login1
org.freedesktop.login1
.
, ( , , . ). , . . , ,
s
u
32- , ,as
a(sb)
, . . D-Bus, .ActivateSession
( , ,s
) ( , , ). , , . .
- , D-Bus. , . . , , . , , - . , . / --, -- ( , , --). :
systemd-logind
SessionNew
- , ,SessionRemoved
, .
- , D-Bus. , , C#. . , , . :
systemd-logind
Docked
b
( ). ,systemd-logind
, - ( ).
D-Bus . , . . , -, HTTP REST. HTTP- D-Bus:
HTTP-, . , VPN. , , . «» D-Bus.
HTTP- . .
HTTP- URL-. URL-, ( , «/») D-Bus.
«» URL- ( , , , ), , . D-Bus .
, HTTP- «?», D-Bus.
, HTTP- D-Bus . , , , .
. , , .
systemd busctl, D-Bus. , . ( --user, ):
$ busctl NAME PID PROCESS USER CONNECTION UNIT SESSION DESCRIPTION :1.1 1 systemd root :1.1 - - - :1.11 705 NetworkManager root :1.11 NetworkManager.service - - :1.14 744 gdm root :1.14 gdm.service - - :1.4 708 systemd-logind root :1.4 systemd-logind.service - - :1.7200 17563 busctl lennart :1.7200 session-1.scope 1 - […] org.freedesktop.NetworkManager 705 NetworkManager root :1.11 NetworkManager.service - - org.freedesktop.login1 708 systemd-logind root :1.4 systemd-logind.service - - org.freedesktop.systemd1 1 systemd root :1.1 - - - org.gnome.DisplayManager 744 gdm root :1.14 gdm.service - - […]
( , ).
, . , ":1.11". D-Bus . , , , . , IP-. , , busctl, . , ( ; , ). DNS, , IP- , , . , , IP-, , . ( , , , IP- , ).
, . , (, , systemd).
. , org.freedesktop.login1:
$ busctl tree org.freedesktop.login1 └─/org/freedesktop/login1 ├─/org/freedesktop/login1/seat │ ├─/org/freedesktop/login1/seat/seat0 │ └─/org/freedesktop/login1/seat/self ├─/org/freedesktop/login1/session │ ├─/org/freedesktop/login1/session/_31 │ └─/org/freedesktop/login1/session/self └─/org/freedesktop/login1/user ├─/org/freedesktop/login1/user/_1000 └─/org/freedesktop/login1/user/self
, ? , , : TAB, . D-Bus!
, . . , , , :
$ busctl introspect org.freedesktop.login1 /org/freedesktop/login1/session/_31
NAME TYPE SIGNATURE RESULT/VALUE FLAGS
org.freedesktop.DBus.Introspectable interface - - -
.Introspect method - s -
org.freedesktop.DBus.Peer interface - - -
.GetMachineId method - s -
.Ping method - - -
org.freedesktop.DBus.Properties interface - - -
.Get method ss v -
.GetAll method s a{sv} -
.Set method ssv - -
.PropertiesChanged signal sa{sv}as - -
org.freedesktop.login1.Session interface - - -
.Activate method - - -
.Kill method si - -
.Lock method - - -
.PauseDeviceComplete method uu - -
.ReleaseControl method - - -
.ReleaseDevice method uu - -
.SetIdleHint method b - -
.TakeControl method b - -
.TakeDevice method uu hb -
.Terminate method - - -
.Unlock method - - -
.Active property b true emits-change
.Audit property u 1 const
.Class property s "user" const
.Desktop property s "" const
.Display property s "" const
.Id property s "1" const
.IdleHint property b true emits-change
.IdleSinceHint property t 1434494624206001 emits-change
.IdleSinceHintMonotonic property t 0 emits-change
.Leader property u 762 const
.Name property s "lennart" const
.Remote property b false const
.RemoteHost property s "" const
.RemoteUser property s "" const
.Scope property s "session-1.scope" const
.Seat property (so) "seat0" "/org/freedesktop/login1/seat... const
.Service property s "gdm-autologin" const
.State property s "active" -
.TTY property s "/dev/tty1" const
.Timestamp property t 1434494630344367 const
.TimestampMonotonic property t 34814579 const
.Type property s "x11" const
.User property (uo) 1000 "/org/freedesktop/login1/user/_1... const
.VTNr property u 1 const
.Lock signal - - -
.PauseDevice signal uus - -
.ResumeDevice signal uuh - -
.Unlock signal - - -
, busctl , , TAB. , , , systemd-logind
. , . . . , . . .
. : - :
# busctl call org.freedesktop.login1 /org/freedesktop/login1/session/_31 org.freedesktop.login1.Session Lock
, , : . - , - , TAB. Lock
, . , , Enter , ( , systemd-logind. GNOME , KDE ).
Lock
, . , . , systemd :
# busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager StartUnit ss "cups.service" "replace"
o "/org/freedesktop/systemd1/job/42684"
, , ( , , ). - . , , . StartUnit systemd , , . . , : ( o ), .
busctl
. , D-Bus ( .cap
Wireshark!) . , sd-bus, busctl
, , .
busctl
( ) API sd-bus. , sd-bus. , . kdbus, D-Bus, !
sd-bus
! , sd-bus.
API sd-bus sd-bus.h.
, .
kdbus, dbus1 .
ssh .
. 34 , PID .
, , , .
, , .
D-Bus UNIX ( ), D-Bus Linux.
, . .
sd-bus
. :
#include <stdio.h>
#include <stdlib.h>
#include <systemd/sd-bus.h>
int main(int argc, char *argv[]) {
sd_bus_error error = SD_BUS_ERROR_NULL;
sd_bus_message *m = NULL;
sd_bus *bus = NULL;
const char *path;
int r;
/* Connect to the system bus */
r = sd_bus_open_system(&bus);
if (r < 0) {
fprintf(stderr, "Failed to connect to system bus: %s\n", strerror(-r));
goto finish;
}
/* Issue the method call and store the respons message in m */
r = sd_bus_call_method(bus,
"org.freedesktop.systemd1", /* service to contact */
"/org/freedesktop/systemd1", /* object path */
"org.freedesktop.systemd1.Manager", /* interface name */
"StartUnit", /* method name */
&error, /* object to return error in */
&m, /* return message on success */
"ss", /* input signature */
"cups.service", /* first argument */
"replace"); /* second argument */
if (r < 0) {
fprintf(stderr, "Failed to issue method call: %s\n", error.message);
goto finish;
}
/* Parse the response message */
r = sd_bus_message_read(m, "o", &path);
if (r < 0) {
fprintf(stderr, "Failed to parse response message: %s\n", strerror(-r));
goto finish;
}
printf("Queued service job as %s.\n", path);
finish:
sd_bus_error_free(&error);
sd_bus_message_unref(m);
sd_bus_unref(bus);
return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
}
bus-client.c
, :
$ gcc bus-client.c -o bus-client `pkg-config --cflags --libs libsystemd`
bus-client
, . root, StartUnit
:
# ./bus-client
Queued service job as /org/freedesktop/systemd1/job/3586.
. , . busctl
, . , . , D-Bus sd-bus. , , , sd-bus.
sd-bus
, - . , . . , : 64- , 64- .
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <systemd/sd-bus.h>
static int method_multiply(sd_bus_message *m, void *userdata, sd_bus_error *ret_error) {
int64_t x, y;
int r;
/* Read the parameters */
r = sd_bus_message_read(m, "xx", &x, &y);
if (r < 0) {
fprintf(stderr, "Failed to parse parameters: %s\n", strerror(-r));
return r;
}
/* Reply with the response */
return sd_bus_reply_method_return(m, "x", x * y);
}
static int method_divide(sd_bus_message *m, void *userdata, sd_bus_error *ret_error) {
int64_t x, y;
int r;
/* Read the parameters */
r = sd_bus_message_read(m, "xx", &x, &y);
if (r < 0) {
fprintf(stderr, "Failed to parse parameters: %s\n", strerror(-r));
return r;
}
/* Return an error on division by zero */
if (y == 0) {
sd_bus_error_set_const(ret_error, "net.poettering.DivisionByZero", "Sorry, can't allow division by zero.");
return -EINVAL;
}
return sd_bus_reply_method_return(m, "x", x / y);
}
/* The vtable of our little object, implements the net.poettering.Calculator interface */
static const sd_bus_vtable calculator_vtable[] = {
SD_BUS_VTABLE_START(0),
SD_BUS_METHOD("Multiply", "xx", "x", method_multiply, SD_BUS_VTABLE_UNPRIVILEGED),
SD_BUS_METHOD("Divide", "xx", "x", method_divide, SD_BUS_VTABLE_UNPRIVILEGED),
SD_BUS_VTABLE_END
};
int main(int argc, char *argv[]) {
sd_bus_slot *slot = NULL;
sd_bus *bus = NULL;
int r;
/* Connect to the user bus this time */
r = sd_bus_open_user(&bus);
if (r < 0) {
fprintf(stderr, "Failed to connect to system bus: %s\n", strerror(-r));
goto finish;
}
/* Install the object */
r = sd_bus_add_object_vtable(bus,
&slot,
"/net/poettering/Calculator", /* object path */
"net.poettering.Calculator", /* interface name */
calculator_vtable,
NULL);
if (r < 0) {
fprintf(stderr, "Failed to issue method call: %s\n", strerror(-r));
goto finish;
}
/* Take a well-known service name so that clients can find us */
r = sd_bus_request_name(bus, "net.poettering.Calculator", 0);
if (r < 0) {
fprintf(stderr, "Failed to acquire service name: %s\n", strerror(-r));
goto finish;
}
for (;;) {
/* Process requests */
r = sd_bus_process(bus, NULL);
if (r < 0) {
fprintf(stderr, "Failed to process bus: %s\n", strerror(-r));
goto finish;
}
if (r > 0) /* we processed a request, try to process another one, right-away */
continue;
/* Wait for the next request to process */
r = sd_bus_wait(bus, (uint64_t) -1);
if (r < 0) {
fprintf(stderr, "Failed to wait on bus: %s\n", strerror(-r));
goto finish;
}
}
finish:
sd_bus_slot_unref(slot);
sd_bus_unref(bus);
return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
}
bus-service.c
, :
$ gcc bus-service.c -o bus-service `pkg-config --cflags --libs libsystemd`
:
$ ./bus-service
. , , , . : , . : , , , . , --user busctl. .
$ busctl --user tree net.poettering.Calculator └─/net/poettering/Calculator
, , , , . , :
$ busctl --user introspect net.poettering.Calculator /net/poettering/Calculator NAME TYPE SIGNATURE RESULT/VALUE FLAGS net.poettering.Calculator interface - - - .Divide method xx x - .Multiply method xx x - org.freedesktop.DBus.Introspectable interface - - - .Introspect method - s - org.freedesktop.DBus.Peer interface - - - .GetMachineId method - s - .Ping method - - - org.freedesktop.DBus.Properties interface - - - .Get method ss v - .GetAll method s a{sv} - .Set method ssv - - .PropertiesChanged signal sa{sv}as - -
, sd-bus . , , , ! , «xx» ( 64- ) «x». ! ?
$ busctl --user call net.poettering.Calculator /net/poettering/Calculator net.poettering.Calculator Multiply xx 5 7 x 35
! 5 7, 35! :
$ busctl --user call net.poettering.Calculator /net/poettering/Calculator net.poettering.Calculator Divide xx 99 17 x 5
! ! ! :
$ busctl --user call net.poettering.Calculator /net/poettering/Calculator net.poettering.Calculator Divide xx 43 0
Sorry, can't allow division by zero.
! . , , .
, . , , , , , . D-Bus sd-bus, ...
Semoga posting ini bermanfaat bagi Anda. Jika Anda tertarik menggunakan sd-bus untuk program Anda sendiri, saya harap ini membantu Anda. Jika Anda memiliki pertanyaan lebih lanjut, lihat halaman manual (tidak lengkap) dan tanyakan kepada kami di IRC atau milis systemd. Jika Anda memerlukan lebih banyak contoh, lihat pohon sumber systemd, semua banyak layanan bus systemd menggunakan sd-bus secara ekstensif.