sd_bus_slot_set_userdata(3) — Linux manual page


SD_BUS_S...USERDATA(3)  sd_bus_slot_set_userdata  SD_BUS_S...USERDATA(3)

NAME         top

       sd_bus_slot_set_userdata, sd_bus_slot_get_userdata - Set and
       query the value in the "userdata" field

SYNOPSIS         top

       #include <systemd/sd-bus.h>

       void* sd_bus_slot_set_userdata(sd_bus_slot* slot,
                                      void* userdata);

       void* sd_bus_slot_get_userdata(sd_bus_slot* slot);

DESCRIPTION         top

       The userdata pointer allows data to be passed between the point
       where a callback is registered, for example when a filter is
       added using sd_bus_add_filter(3) or an asynchronous function call
       is made using sd_bus_call_async(3), and the point where the
       callback is called, without having any global state. The pointer
       has type void* and is not used by the sd-bus functions in any
       way, except to pass to the callback function.

       Usually, the userdata field is set when the slot object is
       initially registered.  sd_bus_slot_set_userdata() may be used to
       change it later for the bus slot object slot. Previous value of
       the field is returned. The argument and returned value may be
       NULL. It will be passed as the userdata argument to the callback
       function attached to the slot.

       sd_bus_slot_set_userdata() gets the value of the userdata field
       in the bus slot object slot.

RETURN VALUE         top

       On success, these functions return the value of the userdata
       field before the function call. If the slot object is NULL, NULL
       will be returned to signify an error, but this is not
       distinguishable from the userdata field value being NULL.

NOTES         top

       Functions described here are available as a shared library, which
       can be compiled against and linked to with the
       libsystemd pkg-config(1) file.

       The code described here uses getenv(3), which is declared to be
       not multi-thread-safe. This means that the code calling the
       functions described here must not call setenv(3) from a parallel
       thread. It is recommended to only do calls to setenv() from an
       early phase of the program when no other threads have been

HISTORY         top

       sd_bus_slot_set_userdata() and sd_bus_slot_get_userdata() were
       added in version 240.

SEE ALSO         top

       systemd(1), sd-bus(3), sd_bus_slot_set_destroy_callback(3),
       sd_bus_add_match(3), sd_bus_slot_get_current_userdata(3)

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

systemd 255                                       SD_BUS_S...USERDATA(3)

Pages that refer to this page: sd-bus(3)sd_bus_slot_set_description(3)sd_bus_slot_set_destroy_callback(3)systemd.directives(7)systemd.index(7)