svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
msgsnap(2)
msgsnap(2) System Calls msgsnap(2)
NAME
msgsnap - message queue snapshot operation
SYNOPSIS
#include <sys/msg.h>
int msgsnap(int msqid, void *buf, size_t bufsz, long msgtyp);
DESCRIPTION
The msgsnap() function reads all of the messages of type msgtyp from
the queue associated with the message queue identifier specified by
msqid and places them in the user-defined buffer pointed to by buf.
The buf argument points to a user-defined buffer that on return will
contain first a buffer header structure:
struct msgsnap_head {
size_t msgsnap_size; /* bytes used/required in the buffer */
size_t msgsnap_nmsg; /* number of messages in the buffer */
};
followed by msgsnap_nmsg messages, each of which starts with a message
header:
struct msgsnap_mhead {
size_t msgsnap_mlen; /* number of bytes in the message */
long msgsnap_mtype; /* message type */
};
and followed by msgsnap_mlen bytes containing the message contents.
Each subsequent message header is located at the first byte following
the previous message contents, rounded up to a sizeof(size_t) boundary.
The bufsz argument specifies the size of buf in bytes. If bufsz is less
than sizeof(msgsnap_head), msgsnap() fails with EINVAL. If bufsz is in‐
sufficient to contain all of the requested messages, msgsnap() succeeds
but returns with msgsnap_nmsg set to 0 and with msgsnap_size set to the
required size of the buffer in bytes.
The msgtyp argument specifies the types of messages requested as fol‐
lows:
o If msgtyp is 0, all of the messages on the queue are read.
o If msgtyp is greater than 0, all messages of type msgtyp are
read.
o If msgtyp is less than 0, all messages with type less than
or equal to the absolute value of msgtyp are read.
The msgsnap() function is a non-destructive operation. Upon completion,
no changes are made to the data structures associated with msqid.
RETURN VALUES
Upon successful completion, msgsnap() returns 0. Otherwise, −1 is re‐
turned and errno is set to indicate the error.
ERRORS
The msgsnap() function will fail if:
EACCES Operation permission is denied to the calling process. See
Intro(2).
EINVAL The msqid argument is not a valid message queue identifier or
the value of bufsz is less than sizeof(struct msgsnap_head).
EFAULT The buf argument points to an illegal address.
USAGE
The msgsnap() function returns a snapshot of messages on a message
queue at one point in time. The queue contents can change immediately
following return from msgsnap().
EXAMPLES
Example 1 msgsnap() example
This is sample C code indicating how to use the msgsnap function (see
msgids(2)).
void
process_msgid(int msqid)
{
size_t bufsize = sizeof(struct msgsnap_head);
struct msgsnap_head *buf;
struct msgsnap_mhead *mhead;
int i;
/* allocate a minimum-size buffer */
buf = malloc(bufsize);
/* read all of the messages from the queue */
for (;;) {
if (msgsnap(msqid, buf, bufsize, 0) != 0) {
perror("msgsnap");
free(buf);
return;
}
if (bufsize >= buf->msgsnap_size) /* we got them all */
break;
/* we need a bigger buffer */
buf = reallocf(buf, buf->msgsnap_size);
if (buf == NULL) {
perror("reallocf");
return;
}
bufsize = buf->msgsnap_size;
}
/* process each message in the queue (there may be none) */
mhead = (struct msgsnap_mhead *)(buf + 1); /* first message */
for (i = 0; i < buf->msgsnap_nmsg; i++) {
size_t mlen = mhead->msgsnap_mlen;
/* process the message contents */
process_message(mhead->msgsnap_mtype, (char *)(mhead + 1),
mlen);
/* advance to the next message header */
mhead = (struct msgsnap_mhead *)
((char *)mhead + sizeof(struct msgsnap_mhead) +
((mlen + sizeof(size_t) - 1) & ~(sizeof(size_t) - 1)));
}
free(buf);
}
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelAsync-Signal-
Safe
SEE ALSO
ipcrm(1), ipcs(1), Intro(2), msgctl(2), msgget(2), msgids(2), ms‐
grcv(2), msgsnd(2), attributes(7)
HISTORY
The msgsnap() function was added to Solaris in the Solaris 8 10/00 (Up‐
date 2) release.
Oracle Solaris 11.4 25 Sep 2020 msgsnap(2)