#include <machine/param.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h> int
shmctl (int shmid int cmd struct shmid_ds *buf);
DESCRIPTION
Performs the action specified by
Fa cmd
on the shared memory segment identified by
Fa shmid :
IPC_STAT
Fetch the segment's
Fa struct shmid_ds ,
storing it in the memory pointed to by
Fa buf .
IPC_SET
Changes the
Fa shm_perm.uid ,
Fa shm_perm.gid ,
and
Fa shm_perm.mode
members of the segment's
Fa struct shmid_ds
to match those of the struct pointed to by
Fa buf .
The calling process's effective uid must
match either
Fa shm_perm.uid
or
Fa shm_perm.cuid ,
or it must have superuser privileges.
IPC_RMID
Removes the segment from the system.
The removal will not take
effect until all processes having attached the segment have exited;
however, once the IPC_RMID operation has taken place, no further
processes will be allowed to attach the segment.
For the operation
to succeed, the calling process's effective uid must match
Fa shm_perm.uid
or
Fa shm_perm.cuid ,
or the process must have superuser privileges.
The
Vt shmid_ds
structure is defined as follows:
struct shmid_ds {
struct ipc_perm shm_perm; /* operation permission structure */
int shm_segsz; /* size of segment in bytes */
pid_t shm_lpid; /* process ID of last shared memory op */
pid_t shm_cpid; /* process ID of creator */
short shm_nattch; /* number of current attaches */
time_t shm_atime; /* time of last shmat() */
time_t shm_dtime; /* time of last shmdt() */
time_t shm_ctime; /* time of last change by shmctl() */
void *shm_internal; /* sysv stupidity */
};
RETURN VALUES
Rv -std shmctl
ERRORS
The
shmctl ();
system call
will fail if:
Bq Er EINVAL
Invalid operation, or
no shared memory segment was found corresponding to
Fa shmid .
Bq Er EPERM
The calling process's effective uid does not match the uid of
the shared memory segment's owner or creator.
Bq Er EACCES
Permission denied due to mismatch between operation and mode of
shared memory segment.
