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4 Copyright (c) 2018-2019 AT&T Intellectual Property.
6 Licensed under the Apache License, Version 2.0 (the "License");
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20 Mnemonic rmr_tralloc_msg.xfm
21 Abstract The manual page for the rmr_tralloc_msg function.
22 Author E. Scott Daniels
27 .im &{lib}/man/setup.im
31 &h1(RMR Library Functions)
40 rmr_mbuf_t* rmr_tralloc_msg( void* vctx, int size,
41 int trace_size, unsigned const char *tr_data );
46 The &cw(rmr_alloc_msg) function is used to allocate a buffer which the user
47 programme can write into and then send through the a library.
48 The buffer is allocated such that sending it requires no additional copying
49 from the buffer as it passes through the underlying transport mechanism.
52 The &ital(size) parameter is used to set the payload length in the message and
53 If it is 0, then the default size supplied on the &ital(rmr_init) call will be used.
54 In addition to allocating the payload, a space in the buffer is
55 reserved for &ital(trace) data (tr_size bytes), and the bytes pointed to
56 by &ital(tr_data) are copied into that portion of the message.
58 The &ital(vctx) parameter is the void context pointer that was returned by
59 the &ital(rmr_init) function.
63 The pointer to the message buffer returned is a structure which has some
64 user application visible fields; the structure is described in &cw(rmr.h,)
65 and is illustrated below.
73 unsigned char* payload;
74 unsigned char* xaction;
79 &beg_dlist(.75i : ^&bold_font )
80 &diitem(state ) Is the current buffer state. Following a call to &cw(rmr_send_msg)
81 the state indicates whether the buffer was successfully sent which determines
82 exactly what the payload points to. If the send failed, the payload referenced
83 by the buffer is the message that failed to send (allowing the application to
84 attempt a retransmission).
85 When the state is &cw(a_OK) the buffer represents an empty buffer that the application
86 may fill in in preparation to send.
89 &diitem(mtype ) When sending a message, the application is expected to set this field
90 to the appropriate message type value (as determined by the user programme). Upon send
91 this value determines how the a library will route the message.
92 For a buffer which has been received, this field will contain the message type that was
93 set by the sending application.
96 &diitem(len ) The application using a buffer to send a message is expected to set the
97 length value to the actual number of bytes that it placed into the message. This
98 is likely less than the total number of bytes that the message can carry.
99 For a message buffer that is passed to the application as the result of a receive
100 call, this will be the value that the sending application supplied and should
101 indicate the number of bytes in the payload which are valid.
104 &diitem(payload ) The payload is a pointer to the actual received data. The
105 user programme may read and write from/to the memory referenced by the payload
106 up until the point in time that the buffer is used on a &cw(rmr_send, rmr_call)
107 or &cw(rmr_reply) function call.
108 Once the buffer has been passed back to a a library function the user programme
109 should &bold(NOT) make use of the payload pointer.
113 &diitem(xaction) The &ital(xaction) field is a pointer to a fixed sized area in
114 the message into which the user may write a transaction ID.
115 The ID is optional with the exception of when the user application uses the &cw(rmr_call)
116 function to send a message and wait for the reply; the underlying a processing
117 expects that the matching reply message will also contain the same data in the
118 &ital(xaction) field.
122 The function returns a pointer to a &cw(rmr_mbuf) structure, or NULL on error.
125 &beg_dlist(.75i : ^&bold_font )
126 &di(ENOMEM) Unable to allocate memory.