shmctl.2

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 2 代码 · 共 166 行

.\" SCCSID: @(#)shmctl.2	8.1	9/11/90
.TH shmctl 2
.SH Name
shmctl \- shared memory control operations
.SH Syntax
.nf
.B #include <\fIsys/types.h\fP>
.B #include <\fIsys/ipc.h\fP>
.B #include <\fIsys/shm.h\fP>
.PP
.B int shmctl (\fIshmid, cmd, buf\fP)
.B int \fIshmid, cmd\fP;
.B struct \fIshmid_ds *buf\fP;
.fi
.SH Description
.NXR "shmctl system call"
.NXR "shmctl system cal" "plock system call"
.NXR "shmctl system call" "shmop system call"
.NXR "shared memory" "control operations"
The
.PN shmctl
system call
provides a variety of shared memory
control operations, as specified by
.IR cmd .
The following 
.I cmds
are available:
.NXR "shmctl system call" "commands"
.TP 15
.B IPC_STAT
Place the current value of each member
of the data structure associated with
.I shmid
into the structure pointed to by 
.IR buf .
The contents of this structure are defined in
.MS intro 2 .
.TP 15
.B IPC_SET
Set the value of the following members
of the data structure associated with
.I shmid
to the corresponding value found
in the structure pointed to by
.IR buf :
.EX
shm_perm.uid
shm_perm.gid
shm_perm.mode    /* only low 9 bits */
.EE
.RS 16
.PP
This 
.I cmd
can only be executed by a process
that has an effective user ID equal to
either that of the superuser or to the value of
.PN shm_perm.uid
in the data structure associated with 
.I shmid.
.RE
.TP 15
.B IPC_RMID
Remove the shared memory identifier specified by 
.I shmid
from the system and destroy the shared
memory segment and data structure
associated with it. This
.I cmd
can only be executed by a process that
has an effective user ID equal to
either that of the superuser or to the value of 
.PN shm_perm.uid
in the data structure associated with
.IR shmid .
.TP 15
.B SHM_LOCK
Lock the shared memory segment specified by
.I shmid
in memory.
Lock prevents the shared memory segment from being swapped
or paged.  This 
.I cmd
can only be executed by a process that has an effective user ID equal to
the superuser.
.TP 15
.B SHM_UNLOCK
Unlock the shared memory segment specified by
.I shmid.
This 
.I cmd
can only be executed by a process that has an effective user ID equal to
the superuser.
.SH Return Values
Upon successful completion, a value of zero (0) is returned.
Otherwise, a value of \-1 is returned, and 
.I errno 
is set to indicated the error.
.SH Diagnostics
.NXR "shmctl system call" "diagnostics"
The
.PN shmctl
system call
fails if any of the following is true:
.TP 15
[EINVAL]
The
.I shmid
is not a valid shared memory identifier. 
.TP 15
[EINVAL]
The
.I cmd
is not a valid command.  
.TP 15
[EACCES]
The
.I cmd
is equal to IPC_STAT,
and read permission is
denied to the calling process.  For further information, see
.MS errno 2 . 
.TP 15
[EPERM]
The
.I cmd
is equal to IPC_RMID or IPC_SET,
and the effective user ID of the
calling process is not equal to that of
the superuser or to the value of
.PN shm_perm.uid
in the data structure associated with
.I shmid. 
.TP 15
[EPERM]
The
.I cmd
is equal to SHM_LOCK
or SHM_UNLOCK
and the effective user ID
of the calling process is not equal to that of the superuser.
.TP 15
[EINVAL]
The
.I cmd
is equal to SHM_LOCK,
and the shared memory segment is currently locked by
this process.
.TP 15
[EINVAL]
The
.I cmd
is equal to SHM_UNLOCK,
and the shared memory segment specified by 
.I shmid
is not currently locked in memory by
this process.
.TP 15
[EFAULT]
The
.I buf
points to an illegal address. 
.SH See Also
shmget(2), shmop(2)