msg.h

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#ifndef _UAPI_LINUX_MSG_H
#define _UAPI_LINUX_MSG_H

#include <linux/ipc.h>

/* ipcs ctl commands */
#define MSG_STAT 11
#define MSG_INFO 12

/* msgrcv options */
#define MSG_NOERROR     010000  /* no error if message is too big */
#define MSG_EXCEPT      020000  /* recv any msg except of specified type.*/

/* Obsolete, used only for backwards compatibility and libc5 compiles */
struct msqid_ds {
    struct ipc_perm msg_perm;
    struct msg *msg_first;      /* first message on queue,unused  */
    struct msg *msg_last;       /* last message in queue,unused */
    __kernel_time_t msg_stime;  /* last msgsnd time */
    __kernel_time_t msg_rtime;  /* last msgrcv time */
    __kernel_time_t msg_ctime;  /* last change time */
    unsigned long  msg_lcbytes; /* Reuse junk fields for 32 bit */
    unsigned long  msg_lqbytes; /* ditto */
    unsigned short msg_cbytes;  /* current number of bytes on queue */
    unsigned short msg_qnum;    /* number of messages in queue */
    unsigned short msg_qbytes;  /* max number of bytes on queue */
    __kernel_ipc_pid_t msg_lspid;   /* pid of last msgsnd */
    __kernel_ipc_pid_t msg_lrpid;   /* last receive pid */
};

/* Include the definition of msqid64_ds */
#include <asm/msgbuf.h>

/* message buffer for msgsnd and msgrcv calls */
struct msgbuf {
    long mtype;         /* type of message */
    char mtext[1];      /* message text */
};

/* buffer for msgctl calls IPC_INFO, MSG_INFO */
struct msginfo {
    int msgpool;
    int msgmap; 
    int msgmax; 
    int msgmnb; 
    int msgmni; 
    int msgssz; 
    int msgtql; 
    unsigned short  msgseg; 
};

/*
 * Scaling factor to compute msgmni:
 * the memory dedicated to msg queues (msgmni * msgmnb) should occupy
 * at most 1/MSG_MEM_SCALE of the lowmem (see the formula in ipc/msg.c):
 * up to 8MB       : msgmni = 16 (MSGMNI)
 * 4 GB            : msgmni = 8K
 * more than 16 GB : msgmni = 32K (IPCMNI)
 */
#define MSG_MEM_SCALE 32

#define MSGMNI    16   /* <= IPCMNI */     /* max # of msg queue identifiers */
#define MSGMAX  8192   /* <= INT_MAX */   /* max size of message (bytes) */
#define MSGMNB 16384   /* <= INT_MAX */   /* default max size of a message queue */

/* unused */
#define MSGPOOL (MSGMNI * MSGMNB / 1024) /* size in kbytes of message pool */
#define MSGTQL  MSGMNB            /* number of system message headers */
#define MSGMAP  MSGMNB            /* number of entries in message map */
#define MSGSSZ  16                /* message segment size */
#define __MSGSEG ((MSGPOOL * 1024) / MSGSSZ) /* max no. of segments */
#define MSGSEG (__MSGSEG <= 0xffff ? __MSGSEG : 0xffff)


#endif /* _UAPI_LINUX_MSG_H */