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sd_varlink_push_fd(3) — Linux manual page

SD_VARLINK_PUSH_FD(3)       sd_varlink_push_fdSD_VARLINK_PUSH_FD(3)

NAME        top

       sd_varlink_push_fd, sd_varlink_push_dup_fd - Submit a file       descriptor to send along with the next outgoing Varlink message

SYNOPSIS        top

#include <systemd/sd-varlink.h>int sd_varlink_push_fd(sd_varlink *link, intfd);int sd_varlink_push_dup_fd(sd_varlink *link, intfd);

DESCRIPTION        top

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 localAF_UNIXonly), 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 tosd_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       tosd_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 onAF_UNIXsockets at once. Attempting to enqueue more on       a single Varlink message will fail with-ENOBUFS.

RETURN VALUE        top

       On success,sd_varlink_push_fd()andsd_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 viasd_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.

NOTES        top

       Functions described here are available as a shared library, which       can be compiled against and linked to with thelibsystemd pkg-config(1) file.       The code described here usesgetenv(3), which is declared to be       not multi-thread-safe. This means that the code calling the       functions described here must not callsetenv(3) from a parallel       thread. It is recommended to only do calls tosetenv()from an       early phase of the program when no other threads have been       started.

HISTORY        top

sd_varlink_push_fd()andsd_varlink_push_dup_fd()were added in       version 257.

SEE ALSO        top

systemd(1),sd-varlink(3)

COLOPHON        top

       This page is part of thesystemd (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 isnot part of the original manual page), send a mail to       man-pages@man7.orgsystemd 258~rc2SD_VARLINK_PUSH_FD(3)

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

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