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man: enchance sd_bus_set_watch_bind() example to handle one more failure

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In case the D-Bus policy is not set up correctly the example just
loops forever. Check the return of sd_bus_request_name_async() in
a callback and exit if the error is not temporary.

Follow-up for 34bbda18a5
This commit is contained in:
Luca Boccassi 2024-02-14 17:14:21 +00:00 committed by Luca Boccassi
parent d0aef638ac
commit e07e7017bb
1 changed files with 23 additions and 5 deletions
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28
man/sd_bus_service_reconnect.c
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@ -5,7 +5,8 @@
* Compile with 'cc sd_bus_service_reconnect.c $(pkg-config --libs --cflags libsystemd)'
*
* To allow the program to take ownership of the name 'org.freedesktop.ReconnectExample',
* add the following as /etc/dbus-1/system.d/org.freedesktop.ReconnectExample.conf:
* add the following as /etc/dbus-1/system.d/org.freedesktop.ReconnectExample.conf
* and then reload the broker with 'systemctl reload dbus':
<?xml version="1.0"?> <!--*-nxml-*-->
<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
@ -92,6 +93,23 @@ static int on_disconnect(sd_bus_message *message, void *userdata, sd_bus_error *
return 0;
}
/* Ensure the event loop exits with a clear error if acquiring the well-known service name fails */
static int request_name_callback(sd_bus_message *m, void *userdata, sd_bus_error *ret_error) {
if (!sd_bus_message_is_method_error(m, NULL))
return 1;
const sd_bus_error *error = sd_bus_message_get_error(m);
if (sd_bus_error_has_names(error, SD_BUS_ERROR_TIMEOUT, SD_BUS_ERROR_NO_REPLY))
return 1; /* The bus is not available, try again later */
printf("Failed to request name: %s\n", error->message);
object *o = userdata;
check(sd_event_exit(*o->event, -sd_bus_error_get_errno(error)));
return 1;
}
static int setup(object *o) {
/* If we are reconnecting, then the bus object needs to be closed, detached from
* the event loop and recreated.
@ -119,7 +137,6 @@ static int setup(object *o) {
check(sd_bus_set_bus_client(*o->bus, 1));
check(sd_bus_negotiate_creds(*o->bus, 1, SD_BUS_CREDS_UID|SD_BUS_CREDS_EUID|SD_BUS_CREDS_EFFECTIVE_CAPS));
check(sd_bus_set_watch_bind(*o->bus, 1));
check(sd_bus_set_connected_signal(*o->bus, 1));
check(sd_bus_start(*o->bus));
/* Publish an interface on the bus, specifying our well-known object access
@ -135,15 +152,16 @@ static int setup(object *o) {
o));
/* By default the service is only assigned an ephemeral name. Also add a well-known
* one, so that clients know whom to call. This needs to be asynchronous, as
* D-Bus might not be yet available.
* D-Bus might not be yet available. The callback will check whether the error is
* expected or not, in case it fails.
* https://www.freedesktop.org/software/systemd/man/sd_bus_request_name.html
*/
check(sd_bus_request_name_async(*o->bus,
NULL,
"org.freedesktop.ReconnectExample",
0,
NULL,
NULL));
request_name_callback,
o));
/* When D-Bus is disconnected this callback will be invoked, which will
* set up the connection again. This needs to be asynchronous, as D-Bus might not
* yet be available.