sd_varlink_send(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON

SD_VARLINK_SEND(3)           sd_varlink_send           SD_VARLINK_SEND(3)

NAME         top

       sd_varlink_send, sd_varlink_sendb, sd_varlink_sendbo - Enqueues a
       Varlink method call, not expecting a reply

SYNOPSIS         top

       #include <systemd/sd-varlink.h>

       int sd_varlink_send(sd_varlink *link, const char *method,
                           sd_json_variant *parameters);

       int sd_varlink_sendb(sd_varlink *link, const char *method, ...);

       int sd_varlink_sendbo(sd_varlink *link, const char *method, ...);

DESCRIPTION         top

       sd_varlink_send() submits a method call via a Varlink connection.
       It takes the Varlink connection object, a method name as string
       parameter, and a JSON object containing the parameters to pass as
       function parameters. This call is asynchronous: the message will
       not be delivered immediately but only once sd_varlink_process(3)
       is invoked (which will happen automatically in one of the
       following event loop iterations if the Varlink connection is
       attached to an even loop).

       sd_varlink_sendb() is similar to sd_varlink_send(), but instead of
       expecting a fully constructed sd_json_variant object carrying the
       parameters, this object is constructed on-the-fly directly from
       the parameter list, in a style identical to sd_json_build(3).

       sd_varlink_sendbo() is identical to sd_varlink_sendb(), but an
       enclosing object is implicitly added, so that the parameter list
       is expected to consist of field pairs only. For details about the
       expected argument list, see sd_json_buildo(3).

       Use sd_varlink_send(), sd_varlink_sendb() and sd_varlink_sendbo()
       only if no method call results are required, as they neither
       provide return parameters nor success/failure information. Use
       sd_varlink_call(3) (and related calls) to submit a method call
       synchronously, returning the server's response.

RETURN VALUE         top

       On success, sd_varlink_send(), sd_varlink_sendb() and
       sd_varlink_sendbo() return a non-negative integer. On failure,
       they return a negative errno-style error code.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           An argument is invalid.

       -ENOMEM
           Memory allocation failed.

       -ENOTCONN
           The Varlink connection object is not connected.

       -EBUSY
           The Varlink connection object is already used for other
           purposes, i.e. executing a method call or similar.

       -ENOBUFS
           The internal limit of queued messages for the Varlink
           connection has been reached. This limit is set very high, and
           hitting it typically indicates that the Varlink connection
           object is stalled — possibly because sd_varlink_process() has
           not been called regularly enough, or because the peer is not
           processing any queued messages. This limit is a safety
           precaution to ensure a stalled peer will not result in
           unbounded memory allocations on the client side.

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
       started.

HISTORY         top

       sd_varlink_send(), sd_varlink_sendb(), sd_varlink_sendbo() were
       added in version 257.

SEE ALSO         top

       systemd(1), sd-varlink(3), sd_varlink_call(3), sd_varlink_build(3)

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have a
       bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11.  (At that
       time, the date of the most recent commit that was found in the
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       (which is not part of the original manual page), send a mail to
       [email protected]

systemd 258~rc2                                        SD_VARLINK_SEND(3)

Pages that refer to this page: systemd.directives(7)systemd.index(7)