добавить массив полей в сообщение D-Bus (append an array of fields to a D-Bus message)
Имя (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
Синопсис (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);
Описание (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 TypesNULL, 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.
Возвращаемое значение (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.
Примечание (Note)
These APIs are implemented as a shared library, which can be
compiled and linked to with the libsystemd pkg-config(1) file.
Смотри также (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
Примечание (Note)
1. Basic Types
http://dbus.freedesktop.org/doc/dbus-specification.html#basic-types
2. The D-Bus specification
http://dbus.freedesktop.org/doc/dbus-specification.html
