sd_bus_message_append_array_space(3)

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NAME

6       sd_bus_message_append_array, sd_bus_message_append_array_memfd,
7       sd_bus_message_append_array_iovec, sd_bus_message_append_array_space -
8       Append an array of fields to a D-Bus message
9

SYNOPSIS

11       #include <systemd/sd-bus.h>
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13       int sd_bus_message_append_array(sd_bus_message *m, char type,
14                                       void *ptr, size_t size);
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16       int sd_bus_message_append_array_memfd(sd_bus_message *m, char type,
17                                             int memfd, uint64_t offset,
18                                             uint64_t size);
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20       int sd_bus_message_append_array_iovec(sd_bus_message *m, char type,
21                                             const struct iovec *iov,
22                                             unsigned n);
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24       int sd_bus_message_append_array_space(sd_bus_message *m, char type,
25                                             size_t size, void **ptr);
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DESCRIPTION

28       The sd_bus_message_append_array() function appends an array to a D-Bus
29       message m. A container will be opened, the array contents appended, and
30       the container closed. The parameter type determines how the pointer p
31       is interpreted.  type must be one of the "trivial" types "y", "n", "q",
32       "i", "u", "x", "t", "d" (but not "b"), as defined by the Basic Types[1]
33       section of the D-Bus specification, and listed in
34       sd_bus_message_append_basic(3). Pointer p must point to an array of
35       size size bytes containing items of the respective type. Size size must
36       be a multiple of the size of the type type. As a special case, p may be
37       NULL, if size is 0. The memory pointed to by p is copied into the
38       memory area containing the message and stays in possession of the
39       caller. The caller may hence freely change the data after this call
40       without affecting the message the array was appended to.
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42       The sd_bus_message_append_array_memfd() function appends an array of a
43       trivial type to message m, similar to sd_bus_message_append_array().
44       The contents of the memory file descriptor memfd starting at the
45       specified offset and of the specified size is used as the contents of
46       the array. The offset and size must be a multiple of the size of the
47       type type. However, as a special exception, if the offset is specified
48       as zero and the size specified as UINT64_MAX the full memory file
49       descriptor contents is used. The memory file descriptor is sealed by
50       this call if it has not been sealed yet, and cannot be modified after
51       this call. See memfd_create(2) for details about memory file
52       descriptors. Appending arrays with memory file descriptors enables
53       efficient zero-copy data transfer, as the memory file descriptor may be
54       passed as-is to the destination, without copying the memory in it to
55       the destination process. Not all protocol transports support passing
56       memory file descriptors between participants, in which case this call
57       will automatically fall back to copying. Also, as memory file
58       descriptor passing is inefficient for smaller amounts of data, copying
59       might still be enforced even where memory file descriptor passing is
60       supported.
61
62       The sd_bus_message_append_array_iovec() function appends an array of a
63       trivial type to the message m, similar to
64       sd_bus_message_append_array(). Contents of the I/O vector array iov are
65       used as the contents of the array. The total size of iov payload (the
66       sum of iov_len fields) must be a multiple of the size of the type type.
67       The iov argument must point to n I/O vector structures. Each structure
68       may have the iov_base field set, in which case the memory pointed to
69       will be copied into the message, or unset (set to zero), in which case
70       a block of zeros of length iov_len bytes will be inserted. The memory
71       pointed at by iov may be changed after this call.
72
73       The sd_bus_message_append_array_space() function appends space for an
74       array of a trivial type to message m. It behaves the same as
75       sd_bus_message_append_array(), but instead of copying items to the
76       message, it returns a pointer to the destination area to the caller in
77       pointer p. The caller should subsequently write the array contents to
78       this memory. Modifications to the memory pointed to should only occur
79       until the next operation on the bus message is invoked. Most
80       importantly, the memory should not be altered anymore when another
81       field has been added to the message or the message has been sealed.
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RETURN VALUE

84       On success, these calls return 0 or a positive integer. On failure,
85       they return a negative errno-style error code.
86
87   Errors
88       Returned errors may indicate the following problems:
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90       -EINVAL
91           Specified parameter is invalid.
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93       -EPERM
94           Message has been sealed.
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96       -ESTALE
97           Message is in invalid state.
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99       -ENXIO
100           Message cannot be appended to.
101
102       -ENOMEM
103           Memory allocation failed.
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NOTES

106       These APIs are implemented as a shared library, which can be compiled
107       and linked to with the libsystemd pkg-config(1) file.
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NOTES

115        1. Basic Types
116           http://dbus.freedesktop.org/doc/dbus-specification.html#basic-types
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118        2. The D-Bus specification
119           http://dbus.freedesktop.org/doc/dbus-specification.html
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123systemd 249                                     SD_BUS_MESSAGE_APPEND_ARRAY(3)

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

NOTES

SEE ALSO

NOTES