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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | SEE ALSO | NOTES | COLOPHON |
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SD_BUS_...ND_ARRAY(3) sd_bus_message_append_array SD_BUS_...ND_ARRAY(3)
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
#include <systemd/sd-bus.h>
int sd_bus_message_append_array(sd_bus_message *m, char type,
const 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);
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.
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.
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.
systemd(1), sd-bus(3), sd_bus_message_append(3),
sd_bus_message_append_basic(3), memfd_create(2), The D-Bus
specification[2]
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
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_BUS_...ND_ARRAY(3)
Pages that refer to this page: sd-bus(3), sd_bus_message_append(3), sd_bus_message_append_strv(3), 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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