Na nova versão do systemd v221, estamos introduzindo a API sd-bus que vem com a versão estável do systemd . sd-bus é nossa biblioteca D-Bus IPC C mínima , suportando tanto D-Bus clássico baseado em soquete quanto kdbus como back-ends . A biblioteca faz parte do systemd há algum tempo, mas foi usada apenas internamente, pois queríamos fazer alterações livremente na API sem afetar os usuários externos. No entanto, agora, a partir da v221, estamos confiantes de que criamos uma API estável.
Neste post, eu forneço uma visão geral da biblioteca sd-bus, uma breve recapitulação dos fundamentos do D-Bus e seus conceitos e alguns exemplos simples de como escrever clientes e serviços D-Bus usando-o.
O que é D-Bus?
Vamos começar com um rápido lembrete do que o D-Bus realmente é. É um poderoso sistema IPC de propósito geral para Linux e outros sistemas operacionais. Ele define conceitos como barramentos, objetos, interfaces, métodos, sinais, propriedades. Ele fornece controle de acesso granular, um sistema de tipo rico, fácil descoberta, autodiagnóstico, monitoramento, multicast confiável, inicialização de serviço, transferências de descritor de arquivo e muito mais. Existem ligações para muitas das linguagens de programação usadas no Linux.
D-Bus tem sido um componente central dos sistemas Linux por mais de 10 anos. É de longe o sistema IPC local de alto nível mais amplamente usado no Linux. Desde seu início, o systemd é o sistema IPC no qual expõe suas interfaces. E mesmo antes do systemd, era o sistema IPC que o Upstart usava para suas interfaces. É usado pelo GNOME, KDE e muitos componentes do sistema.
D-Bus , . , . , , , - , . ( kdbus .)
D-Bus IPC AF_UNIX. TCP/IP. , D-Bus TCP . D-Bus , ssh, . systemd , API .
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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.
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sd-bus.
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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 - - […]
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. , 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 - - -
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# busctl call org.freedesktop.login1 /org/freedesktop/login1/session/_31 org.freedesktop.login1.Session Lock
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# busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager StartUnit ss "cups.service" "replace"
o "/org/freedesktop/systemd1/job/42684"
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#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, ...
Espero que esta postagem tenha sido útil para você. Se você estiver interessado em usar o barramento SD para seus próprios programas, espero que ajude você. Se você tiver mais perguntas, dê uma olhada nas páginas do manual (incompletas) e pergunte-nos no IRC ou na lista de discussão do systemd. Se você precisar de mais exemplos, dê uma olhada na árvore de origem do systemd, todos os muitos serviços de barramento do systemd usam extensivamente o barramento sd.