'\" t .TH "SD_BUS_MESSAGE_APPEND_ARRAY" "3" "" "systemd 257" "sd_bus_message_append_array" .\" ----------------------------------------------------------------- .\" * Define some portability stuff .\" ----------------------------------------------------------------- .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .\" http://bugs.debian.org/507673 .\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .ie \n(.g .ds Aq \(aq .el .ds Aq ' .\" ----------------------------------------------------------------- .\" * set default formatting .\" ----------------------------------------------------------------- .\" disable hyphenation .nh .\" disable justification (adjust text to left margin only) .ad l .\" ----------------------------------------------------------------- .\" * MAIN CONTENT STARTS HERE * .\" ----------------------------------------------------------------- .SH "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 .SH "SYNOPSIS" .sp .ft B .nf #include .fi .ft .HP \w'int\ sd_bus_message_append_array('u .BI "int sd_bus_message_append_array(sd_bus_message\ *" "m" ", char\ " "type" ", const\ void\ *" "ptr" ", size_t\ " "size" ");" .HP \w'int\ sd_bus_message_append_array_memfd('u .BI "int sd_bus_message_append_array_memfd(sd_bus_message\ *" "m" ", char\ " "type" ", int\ " "memfd" ", uint64_t\ " "offset" ", uint64_t\ " "size" ");" .HP \w'int\ sd_bus_message_append_array_iovec('u .BI "int sd_bus_message_append_array_iovec(sd_bus_message\ *" "m" ", char\ " "type" ", const\ struct\ iovec\ *" "iov" ", unsigned\ " "n" ");" .HP \w'int\ sd_bus_message_append_array_space('u .BI "int sd_bus_message_append_array_space(sd_bus_message\ *" "m" ", char\ " "type" ", size_t\ " "size" ", void\ **" "ptr" ");" .SH "DESCRIPTION" .PP The \fBsd_bus_message_append_array()\fR function appends an array to a D\-Bus message \fIm\fR\&. A container will be opened, the array contents appended, and the container closed\&. The parameter \fItype\fR determines how the pointer \fIp\fR is interpreted\&. \fItype\fR must be one of the "trivial" types "y", "n", "q", "i", "u", "x", "t", "d" (but not "b"), as defined by the \m[blue]\fBBasic D\-Bus Types\fR\m[]\&\s-2\u[1]\d\s+2 section of the D\-Bus specification, and listed in \fBsd_bus_message_append_basic\fR(3)\&. Pointer \fIp\fR must point to an array of size \fIsize\fR bytes containing items of the respective type\&. Size \fIsize\fR must be a multiple of the size of the type \fItype\fR\&. As a special case, \fIp\fR may be \fBNULL\fR, if \fIsize\fR is 0\&. The memory pointed to by \fIp\fR 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\&. .PP The \fBsd_bus_message_append_array_memfd()\fR function appends an array of a trivial type to message \fIm\fR, similar to \fBsd_bus_message_append_array()\fR\&. The contents of the memory file descriptor \fImemfd\fR 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 \fItype\fR\&. 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 \fBmemfd_create\fR(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\&. .PP The \fBsd_bus_message_append_array_iovec()\fR function appends an array of a trivial type to the message \fIm\fR, similar to \fBsd_bus_message_append_array()\fR\&. Contents of the I/O vector array \fIiov\fR are used as the contents of the array\&. The total size of \fIiov\fR payload (the sum of \fIiov_len\fR fields) must be a multiple of the size of the type \fItype\fR\&. The \fIiov\fR argument must point to \fIn\fR 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 \fIiov\fR may be changed after this call\&. .PP The \fBsd_bus_message_append_array_space()\fR function appends space for an array of a trivial type to message \fIm\fR\&. It behaves the same as \fBsd_bus_message_append_array()\fR, but instead of copying items to the message, it returns a pointer to the destination area to the caller in pointer \fIp\fR\&. 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\&. .SH "RETURN VALUE" .PP On success, these calls return 0 or a positive integer\&. On failure, they return a negative errno\-style error code\&. .SS "Errors" .PP Returned errors may indicate the following problems: .PP \fB\-EINVAL\fR .RS 4 Specified parameter is invalid\&. .RE .PP \fB\-EPERM\fR .RS 4 Message has been sealed\&. .RE .PP \fB\-ESTALE\fR .RS 4 Message is in invalid state\&. .RE .PP \fB\-ENXIO\fR .RS 4 Message cannot be appended to\&. .RE .PP \fB\-ENOMEM\fR .RS 4 Memory allocation failed\&. .RE .SH "NOTES" .PP Functions described here are available as a shared library, which can be compiled against and linked to with the \fBlibsystemd\fR\ \&\fBpkg-config\fR(1) file\&. .PP The code described here uses \fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call \fBsetenv\fR(3) from a parallel thread\&. It is recommended to only do calls to \fBsetenv()\fR from an early phase of the program when no other threads have been started\&. .SH "SEE ALSO" .PP \fBsystemd\fR(1), \fBsd-bus\fR(3), \fBsd_bus_message_append\fR(3), \fBsd_bus_message_append_basic\fR(3), \fBmemfd_create\fR(2), \m[blue]\fBThe D\-Bus specification\fR\m[]\&\s-2\u[2]\d\s+2 .SH "NOTES" .IP " 1." 4 Basic D-Bus Types .RS 4 \%https://dbus.freedesktop.org/doc/dbus-specification.html#basic-types .RE .IP " 2." 4 The D-Bus specification .RS 4 \%https://dbus.freedesktop.org/doc/dbus-specification.html .RE