Man Page: rmr_tralloc_msg¶

RMR LIBRARY FUNCTIONS¶

NAME¶

rmr_tralloc_msg

SYNOPSIS¶

#include <rmr/rmr.h>

rmr_mbuf_t* rmr_tralloc_msg( void* vctx, int size,
                             int trace_size, unsigned const char *tr_data );

DESCRIPTION¶

The rmr_tralloc_msg function is used to allocate a buffer which the user programme can write into and then send through the library. The buffer is allocated such that sending it requires no additional copying from the buffer as it passes through the underlying transport mechanism.

The size parameter is used to set the payload length in the message. If it is 0, then the default size supplied on the rmr_init call will be used. In addition to allocating the payload, a space in the buffer is reserved for trace data (tr_size bytes), and the bytes pointed to by tr_data are copied into that portion of the message. The vctx parameter is the void context pointer that was returned by the rmr_init function.

The pointer to the message buffer returned is a structure which has some user application visible fields; the structure is described in rmr.h, and is illustrated below.

typedef struct {
    int state;
    int mtype;
    int len;
    unsigned char* payload;
    unsigned char* xaction;
} rmr_mbuf_t;

Where:

state

Is the current buffer state. Following a call to rmr_send_msg the state indicates whether the buffer was successfully sent which determines exactly what the payload points to. If the send failed, the payload referenced by the buffer is the message that failed to send (allowing the application to attempt a retransmission). When the state is a_OK the buffer represents an empty buffer that the application may fill in in preparation to send.

mtype

When sending a message, the application is expected to set this field to the appropriate message type value (as determined by the user programme). Upon send this value determines how the a library will route the message. For a buffer which has been received, this field will contain the message type that was set by the sending application.

len

The application using a buffer to send a message is expected to set the length value to the actual number of bytes that it placed into the message. This is likely less than the total number of bytes that the message can carry. For a message buffer that is passed to the application as the result of a receive call, this will be the value that the sending application supplied and should indicate the number of bytes in the payload which are valid.

payload

The payload is a pointer to the actual received data. The user programme may read and write from/to the memory referenced by the payload up until the point in time that the buffer is used on a rmr_send, rmr_call or rmr_reply function call. Once the buffer has been passed back to a a library function the user programme should NOT make use of the payload pointer.

xaction

The xaction field is a pointer to a fixed sized area in the message into which the user may write a transaction ID. The ID is optional with the exception of when the user application uses the rmr_call function to send a message and wait for the reply; the underlying processing expects that the matching reply message will also contain the same data in the xaction field.

RETURN VALUE¶

The function returns a pointer to a rmr_mbuf structure, or NULL on error.

ERRORS¶

ENOMEM

Unable to allocate memory.