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.
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.