NAME

       sd_bus_message_append_array, sd_bus_message_append_array_memfd,
       sd_bus_message_append_array_iovec, sd_bus_message_append_array_space - Append an array of
       fields to a D-Bus message

SYNOPSIS

       #include <systemd/sd-bus.h>

       int sd_bus_message_append_array(sd_bus_message *m, char type, void *ptr, size_t size);

       int sd_bus_message_append_array_memfd(sd_bus_message *m, char type, int memfd,
                                             uint64_t offset, uint64_t size);

       int sd_bus_message_append_array_iovec(sd_bus_message *m, char type,
                                             const struct iovec *iov, unsigned n);

       int sd_bus_message_append_array_space(sd_bus_message *m, char type, size_t size,
                                             void **ptr);

DESCRIPTION

       The sd_bus_message_append_array() function appends an array to a D-Bus message m. A
       container will be opened, the array contents appended, and the container closed. The
       parameter type determines how the pointer p is interpreted.  type must be one of the
       "trivial" types "y", "n", "q", "i", "u", "x", "t", "d" (but not "b"), as defined by the
       Basic D-Bus Types[1] section of the D-Bus specification, and listed in
       sd_bus_message_append_basic(3). Pointer p must point to an array of size size bytes
       containing items of the respective type. Size size must be a multiple of the size of the
       type type. As a special case, p may be NULL, if size is 0. The memory pointed to by p is
       copied into the memory area containing the message and stays in possession of the caller.
       The caller may hence freely change the data after this call without affecting the message
       the array was appended to.

       The sd_bus_message_append_array_memfd() function appends an array of a trivial type to
       message m, similar to sd_bus_message_append_array(). The contents of the memory file
       descriptor memfd starting at the specified offset and of the specified size is used as the
       contents of the array. The offset and size must be a multiple of the size of the type
       type. However, as a special exception, if the offset is specified as zero and the size
       specified as UINT64_MAX the full memory file descriptor contents is used. The memory file
       descriptor is sealed by this call if it has not been sealed yet, and cannot be modified
       after this call. See memfd_create(2) for details about memory file descriptors. Appending
       arrays with memory file descriptors enables efficient zero-copy data transfer, as the
       memory file descriptor may be passed as-is to the destination, without copying the memory
       in it to the destination process. Not all protocol transports support passing memory file
       descriptors between participants, in which case this call will automatically fall back to
       copying. Also, as memory file descriptor passing is inefficient for smaller amounts of
       data, copying might still be enforced even where memory file descriptor passing is
       supported.

       The sd_bus_message_append_array_iovec() function appends an array of a trivial type to the
       message m, similar to sd_bus_message_append_array(). Contents of the I/O vector array iov
       are used as the contents of the array. The total size of iov payload (the sum of iov_len
       fields) must be a multiple of the size of the type type. The iov argument must point to n
       I/O vector structures. Each structure may have the iov_base field set, in which case the
       memory pointed to will be copied into the message, or unset (set to zero), in which case a
       block of zeros of length iov_len bytes will be inserted. The memory pointed at by iov may
       be changed after this call.

       The sd_bus_message_append_array_space() function appends space for an array of a trivial
       type to message m. It behaves the same as sd_bus_message_append_array(), but instead of
       copying items to the message, it returns a pointer to the destination area to the caller
       in pointer p. The caller should subsequently write the array contents to this memory.
       Modifications to the memory pointed to should only occur until the next operation on the
       bus message is invoked. Most importantly, the memory should not be altered anymore when
       another field has been added to the message or the message has been sealed.

RETURN VALUE

       On success, these calls return 0 or a positive integer. On failure, they return a negative
       errno-style error code.

   Errors
       Returned errors may indicate the following problems:

       -EINVAL
           Specified parameter is invalid.

       -EPERM
           Message has been sealed.

       -ESTALE
           Message is in invalid state.

       -ENXIO
           Message cannot be appended to.

       -ENOMEM
           Memory allocation failed.

NOTES

       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.

SEE ALSO

       systemd(1), sd-bus(3), sd_bus_message_append(3), sd_bus_message_append_basic(3),
       memfd_create(2), The D-Bus specification[2]

NOTES

        1. Basic D-Bus Types
           https://dbus.freedesktop.org/doc/dbus-specification.html#basic-types

        2. The D-Bus specification
           https://dbus.freedesktop.org/doc/dbus-specification.html