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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_VARLINK_PUSH_FD(3) sd_varlink_push_fd SD_VARLINK_PUSH_FD(3)
sd_varlink_push_fd, sd_varlink_push_dup_fd - Submit a file
descriptor to send along with the next outgoing Varlink message
#include <systemd/sd-varlink.h>
int sd_varlink_push_fd(sd_varlink *link, int fd);
int sd_varlink_push_dup_fd(sd_varlink *link, int fd);
sd_varlink_push_fd() submits a file descriptor to send along with
the next outgoing Varlink message. Takes a Varlink connection
object and a file descriptor as parameter. The file descriptor is
not duplicated, and hence ownership of the file descriptor is
passed to the Varlink connection object (only on success; on
failure the caller retains ownership). Once the file descriptor
has been written to the underlying transport socket it is
automatically closed. The calling application code should not
touch the file descriptor or close it on its own, otherwise it
will interfere with the Varlink protocol implementation. This call
is only supported if the backing transport supports file
descriptor passing (effectively this means the functionality is
supported on local AF_UNIX only), and the concept is not part of
the Varlink protocol, but simply a feature of the underlying
transport.
sd_varlink_push_dup_fd() is identical to sd_varlink_push_fd(),
except that the file descriptor is duplicated automatically, and
the calling application code hence retains ownership of the
provided file descriptor, and must close it on its own.
Note that file descriptor passing is only permitted after a call
to sd_varlink_set_allow_fd_passing_output() that enables it,
otherwise these calls will fail with -EPERM.
Note that on Linux a maximum of 253 file descriptors may be
enqueued on AF_UNIX sockets at once. Attempting to enqueue more on
a single Varlink message will fail with -ENOBUFS.
On success, sd_varlink_push_fd() and sd_varlink_push_dup_fd()
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.
-EBADF
The provided file descriptor is not valid.
-EPERM
File descriptor passing has not been enabled via
sd_varlink_set_allow_fd_passing_output().
-ENOBUFS
The maximum of 253 file descriptors have already been
submitted for the next outgoing Varlink message, no further
descriptors may be enqueued for this message.
-ENOMEM
Memory allocation failed.
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.
sd_varlink_push_fd() and sd_varlink_push_dup_fd() were added in
version 257.
systemd(1), sd-varlink(3)
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
repository was 2025-08-11.) 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
[email protected]
systemd 258~rc2 SD_VARLINK_PUSH_FD(3)
Pages that refer to this page: systemd.directives(7), systemd.index(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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