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man pages section 2: System Calls     Oracle Solaris 10 1/13 Information Library
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Document Information

Preface

Introduction

System Calls

access(2)

acct(2)

acl(2)

adjtime(2)

alarm(2)

audit(2)

auditon(2)

auditsvc(2)

brk(2)

chdir(2)

chmod(2)

chown(2)

chroot(2)

close(2)

creat(2)

dup(2)

exec(2)

execl(2)

execle(2)

execlp(2)

execv(2)

execve(2)

execvp(2)

_Exit(2)

_exit(2)

exit(2)

facl(2)

fchdir(2)

fchmod(2)

fchown(2)

fchownat(2)

fchroot(2)

fcntl(2)

fgetlabel(2)

fork1(2)

fork(2)

forkall(2)

fpathconf(2)

fstat(2)

fstatat(2)

fstatvfs(2)

futimens(2)

futimesat(2)

getacct(2)

getaudit(2)

getaudit_addr(2)

getauid(2)

getcontext(2)

getdents(2)

getegid(2)

geteuid(2)

getgid(2)

getgroups(2)

getisax(2)

getitimer(2)

getlabel(2)

getmsg(2)

getpflags(2)

getpgid(2)

getpgrp(2)

getpid(2)

getpmsg(2)

getppid(2)

getppriv(2)

getprojid(2)

getrctl(2)

getrlimit(2)

getsid(2)

gettaskid(2)

getuid(2)

getustack(2)

ioctl(2)

issetugid(2)

kill(2)

lchown(2)

link(2)

llseek(2)

lseek(2)

lstat(2)

_lwp_cond_broadcast(2)

_lwp_cond_reltimedwait(2)

_lwp_cond_signal(2)

_lwp_cond_timedwait(2)

_lwp_cond_wait(2)

_lwp_continue(2)

_lwp_info(2)

_lwp_kill(2)

_lwp_mutex_lock(2)

_lwp_mutex_trylock(2)

_lwp_mutex_unlock(2)

_lwp_self(2)

_lwp_sema_init(2)

_lwp_sema_post(2)

_lwp_sema_trywait(2)

_lwp_sema_wait(2)

_lwp_suspend(2)

memcntl(2)

meminfo(2)

mincore(2)

mkdir(2)

mknod(2)

mmap(2)

mount(2)

mprotect(2)

msgctl(2)

msgget(2)

msgids(2)

msgrcv(2)

msgsnap(2)

msgsnd(2)

munmap(2)

nice(2)

ntp_adjtime(2)

ntp_gettime(2)

open(2)

openat(2)

pathconf(2)

pause(2)

pcsample(2)

pipe(2)

poll(2)

p_online(2)

pread(2)

priocntl(2)

priocntlset(2)

processor_bind(2)

processor_info(2)

profil(2)

pset_assign(2)

pset_bind(2)

pset_create(2)

pset_destroy(2)

pset_getattr(2)

pset_info(2)

pset_list(2)

pset_setattr(2)

putacct(2)

putmsg(2)

putpmsg(2)

pwrite(2)

read(2)

readlink(2)

readv(2)

rename(2)

renameat(2)

resolvepath(2)

rmdir(2)

sbrk(2)

semctl(2)

semget(2)

semids(2)

semop(2)

semtimedop(2)

setaudit(2)

setaudit_addr(2)

setauid(2)

setcontext(2)

setegid(2)

seteuid(2)

setgid(2)

setgroups(2)

setitimer(2)

setpflags(2)

setpgid(2)

setpgrp(2)

setppriv(2)

setrctl(2)

setregid(2)

setreuid(2)

setrlimit(2)

setsid(2)

settaskid(2)

setuid(2)

setustack(2)

shmat(2)

shmctl(2)

shmdt(2)

shmget(2)

shmids(2)

shmop(2)

sigaction(2)

sigaltstack(2)

sigpending(2)

sigprocmask(2)

sigsend(2)

sigsendset(2)

sigsuspend(2)

sigwait(2)

__sparc_utrap_install(2)

stat(2)

statvfs(2)

stime(2)

swapctl(2)

symlink(2)

sync(2)

sysfs(2)

sysinfo(2)

time(2)

times(2)

uadmin(2)

ulimit(2)

umask(2)

umount(2)

umount2(2)

uname(2)

unlink(2)

unlinkat(2)

ustat(2)

utime(2)

utimensat(2)

utimes(2)

uucopy(2)

vfork(2)

vhangup(2)

waitid(2)

wracct(2)

write(2)

writev(2)

yield(2)

msgsnap

- message queue snapshot operation

Synopsis

#include <sys/msg.h>

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 insufficient 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 follows:

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 returned 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;
     struct msgsnap_head *buf;
     struct msgsnap_mhead *mhead;
     int i;

     /* allocate a minimum-size buffer */
     buf = malloc(bufsize = sizeof(struct msgsnap_head));

     /* 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 = realloc(buf, 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(5) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
MT-Level
Async-Signal-Safe

See Also

ipcrm(1), ipcs(1), Intro(2), msgctl(2), msgget(2), msgids(2), msgrcv(2), msgsnd(2), attributes(5)