shmop.2

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)shmop.2	8.1	9/11/90
.TH shmop 2
.SH Name
shmop, shmat, shmdt \- shared memory operations
.SH Syntax
.ft B
.nf
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
.PP
.ft B
char *shmat (shmid, shmaddr, shmflg)
int shmid;
char *shmaddr;
int shmflg;
.PP
.ft B
int shmdt (shmaddr)
char *shmaddr;
.fi
.SH Description
.NXR "shmop system call"
.NXR "shmat system call"
.NXR "shmdt system call"
.NXA "shmat system call" "shmctl system call"
.NXA "shmdt system call" "shmget system call"
.NXR "shared memory" "operations"
The
.PN shmat
system call attaches the shared memory segment
associated with the shared memory identifier specified by 
.I shmid
to the data segment of the calling process.
The segment is attached at the address
specified by one of the following criteria:
.PP
If
.I shmaddr 
is equal to zero, the segment is attached
at the first available address as
selected by the system.
.PP
If
.I shmaddr
is not equal to zero and 
.RI ( shmflg
& SHM_RND )
is true, the segment is attached
at the address given by 
.RI ( shmaddr \- 
.RI ( shmaddr
modulus
SHMLBA )).
.PP
If
.I shmaddr
is not equal to zero and 
.RI ( shmflg
& SHM_RND )
is false, the segment is attached
at the address given by
.I shmaddr.
.PP
The segment is attached for reading if 
.RI ( shmflg
& SHM_RDONLY )
is true. Otherwise, it is
attached for reading and writing. 
.PP
The
.PN shmdt
system call detaches from the calling process's
data segment the shared memory segment
located at the address specified by
.I shmaddr.
.SH Return Values
Upon successful completion, the return values are as follows:
.IP \(bu 4
The
.PN shmat
system call
returns the data segment start address
of the attached shared memory segment.
.IP \(bu
The
.PN shmdt
system call returns a value of zero (0).
.PP
Otherwise, a value of \-1 is returned, and 
.I errno
is set to indicate the error.
.SH Diagnostics
The
.PN shmat
system call
fails and not attach the shared memory segment, if any of the
following is true:
.TP 15
[EINVAL]
The
.I shmid 
is not a valid shared memory identifier. 
.TP 15
[EACCES]
Operation permission is denied to the calling process.  For further
information, see 
.MS errno 2 . 
.TP 15
[ENOMEM]
The available data space is not large
enough to accommodate the shared memory segment. 
.TP 15
[EINVAL]
The
.I shmaddr
is not equal to zero, and the value of 
.RI ( shmaddr \-
.RI ( shmaddr
modulus SHMLBA ))
is an illegal address.
.TP 15
[EINVAL]
The
.I shmaddr
is not equal to zero, 
.RI ( shmflg
& SHM_RND )
is false, and the value of
.I shmaddr
is an illegal address. 
.TP 15
[EMFILE]
The number of shared memory segments
attached to the calling process would
exceed the system imposed limit. 
.PP
The
.PN shmdt
fails and does not detach the shared memory segment if:
.TP 15
[EINVAL]
The
.I shmaddr
is not the data segment start
address of a shared memory segment. 
.SH See Also
execve(2), exit(2), fork(2), shmctl(2), shmget(2)