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1.1 root 1:
2:
3: msgrcv() COHERENT System Call msgrcv()
4:
5:
6:
7:
8: Receive a message
9:
10: #include <sys/msg.h>
11: mmssggrrccvv(_m_s_q_i_d, _m_s_g_p, _m_s_g_s_z, _m_s_g_t_y_p, _m_s_g_f_l_g)
12: iinntt _m_s_q_i_d, _m_s_g_s_z, _m_s_g_f_l_g; ssttrruucctt mmssggbbuuff *_m_s_g_p; lloonngg _m_s_g_t_y_p;
13:
14: msgrcv reads a message from the queue associated with the queue
15: identifier msqid and writes it in the structure pointed to by
16: msgp. This structure consists of the following members:
17:
18:
19: long mtype; /* message type */
20: char mtext[]; /* message text */
21:
22:
23: mtype is the received message's type, as specified by the sending
24: process. mtext is the text of the message. msgsz gives the size
25: of mtext, in bytes. The received message is truncated to msgsz
26: bytes if it is larger than msgsz and (_m_s_g_f_l_g & MMSSGG_NNOOEERRRROORR) is
27: true. The truncated portion of the message is lost, with no in-
28: dication given to the calling process.
29:
30: msgtyp specifies the type of message requested, as follows:
31:
32: * If msgtyp equals 0L, the first message on the queue is
33: received.
34:
35: * If msgtyp is greater than 0L, the first message of type msgtyp
36: is received.
37:
38: * If msgtyp is less than 0L, the first message of the lowest
39: type that is less than or equal to the absolute value of
40: msgtyp is received.
41:
42: msgflg specifies the action taken if a message of the desired
43: type is not on the queue, as follows:
44:
45: * If (_m_s_g_f_l_g & IIPPCC_NNOOWWAAIITT) is true, the calling process im-
46: mediately returns -1 and sets errno to ENOMSG.
47:
48: * If (_m_s_g_f_l_g & IIPPCC_NNOOWWAAIITT) is false, the calling process
49: suspends execution until one of the following occurs:
50:
51: 11. A message of the desired type is placed on the queue.
52:
53: 22. msqid is removed from the system. When this occurs, msgrcv
54: sets errno to EDOM
55:
56: 33. The calling process receives a signal that is to be caught.
57: In this case, a message is not received and the calling
58: process resumes execution in the manner prescribed in signal.
59:
60: msgrcv fails and no message is received if any of the following
61: is true:
62:
63:
64: COHERENT Lexicon Page 1
65:
66:
67:
68:
69: msgrcv() COHERENT System Call msgrcv()
70:
71:
72:
73:
74: * msqid is not a valid message queue identifier. msgrcv errno
75: to EINVAL.
76:
77: * Operation permission is denied to the calling process
78: (EEAACCCCEESS).
79:
80: * msgsz is less than zero (EEIINNVVAALL).
81:
82: * mtext is greater than msgsz and (_m_s_g_f_l_g & MMSSGG_NNOOEERRRROORR) is
83: false (EE22BBIIGG).
84:
85: * The queue does not contain a message of the desired type and
86: (_m_s_g_t_y_p & IIPPCC_NNOOWWAAIITT) is true (EENNOOMMSSGG).
87:
88: * msgp points to an illegal address (EEFFAAUULLTT).
89:
90: Upon successful completion, the following actions are taken with
91: respect to the data structure associated with msqid:
92:
93: * msg_qnum is decremented by one.
94:
95: * msg_lrpid is set equal to the process identifier of the
96: calling process.
97:
98: * msg_rtime is set equal to the current time.
99:
100: ***** Return Values *****
101:
102: If msgrcv returns due to the receipt of a signal, it returns -1
103: and sets errno to EINTR. If it returns due to the removal of
104: msqid from the system, it returns -1 and sets errno to EDOM.
105: Upon successful completion, msgrcv returns a value equal to the
106: number of bytes written into mtext. Otherwise, it returns -1 and
107: sets errno to an appropriate value.
108:
109: ***** Files *****
110:
111: /usr/include/sys/ipc.h
112: /usr/include/sys/msg.h
113: /dev/msg
114:
115: ***** See Also *****
116:
117: COHERENT system calls, msg, msgctl(), msgget(), msgsnd()
118:
119: ***** Notes *****
120:
121: To improve portability, the COHERENT system implements the mmssgg as
122: a device driver rather than as an actual system call.
123:
124:
125:
126:
127:
128:
129:
130: COHERENT Lexicon Page 2
131:
132:
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