svmsg/svmsg_file.h

This is svmsg/svmsg_file.h (Listing 46-7, page 956), an example from the book, The Linux Programming Interface.

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/* svmsg_file.h

   Header file for svmsg_file_server.c and svmsg_file_client.c.
*/
#include <sys/types.h>
#include <sys/msg.h>
#include <sys/stat.h>
#include <stddef.h>                     /* For definition of offsetof() */
#include <limits.h>
#include <fcntl.h>
#include <signal.h>
#include <sys/wait.h>
#include "tlpi_hdr.h"

#define SERVER_KEY 0x1aaaaaa1           /* Key for server's message queue */

struct requestMsg {                     /* Requests (client to server) */
    long mtype;                         /* Unused */
    int  clientId;                      /* ID of client's message queue */
    char pathname[PATH_MAX];            /* File to be returned */
};

/* REQ_MSG_SIZE computes size of 'mtext' part of 'requestMsg' structure.
   We use offsetof() to handle the possibility that there are padding
   bytes between the 'clientId' and 'pathname' fields. */

#define REQ_MSG_SIZE (offsetof(struct requestMsg, pathname) - \
                      offsetof(struct requestMsg, clientId) + PATH_MAX)

#define RESP_MSG_SIZE 8192

struct responseMsg {                    /* Responses (server to client) */
    long mtype;                         /* One of RESP_MT_* values below */
    char data[RESP_MSG_SIZE];           /* File content / response message */
};

/* Types for response messages sent from server to client */

#define RESP_MT_FAILURE 1               /* File couldn't be opened */
#define RESP_MT_DATA    2               /* Message contains file data */
#define RESP_MT_END     3               /* File data complete */

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