SHMOP(S) XENIX System V SHMOP(S)
Name
shmop - Performs shared memory operations.
Syntax
For 386 processes:
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
char *shmat (shmid, shmaddr, shmflg)
int shmid;
char *shmaddr;
int shmflg;
int shmdt (shmaddr)
char *shmaddr;
For 286 processes:
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
char far *shmat (shmid, shmaddr, shmflg)
int shmid;
char far *shmaddr;
int shmflg;
int shmdt (shmaddr)
char far *shmaddr;
Description
shmat attaches the shared memory segment associated with the
shared memory identifier specified by shmid to the data
segment of the calling process. The segment is attached at
the address specified by one of the following criteria:
If shmaddr is equal to zero, the segment is attached at
the first available address as selected by the system.
For 286 processes, if shmaddr is not equal to zero and
(shmflg & SHM_RND) is ``true,'' the segment is attached
at the first available address given by (shmaddr -
(shmaddr modulus SHMLBA)) (SHMLBA = 64K or 65536
bytes).
If shmaddr is not equal to zero and (shmflg & SHM_RND)
is ``true'', the segment is attached at the address
given by (shmaddr - (shmaddr modulus SHMLBA)).
If shmaddr is not equal to zero and (shmflg & SHM_RND)
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is ``false'', the segment is attached at the address
given by shmaddr.
The segment is attached for reading if (shmflg & SHM_RDONLY)
is ``true'', otherwise it is attached for reading and
writing.
shmdt detaches from the calling process's data segment the
shared memory segment located at the address specified by
shmaddr. shmat will fail and not attach the shared memory
segment if one or more of the following are true:
shmid is not a valid shared memory identifier.
[EINVAL]
Operation permission is denied to the calling process
(see intro(S)). [EACCES]
The available data space is not large enough to
accommodate the shared memory segment. [ENOMEM]
shmaddr is not equal to zero, and the value of (shmaddr
- (shmaddr modulus SHMLBA)) is an illegal address.
[EINVAL]
shmaddr is not equal to zero, (shmflg & SHM_RND) is
``false'', and the value of shmaddr is an illegal
address. [EINVAL]
For 286 processes, the shared memory segment is already
attached by the calling process. [EINVAL]
The number of shared memory segments attached to the
calling process would exceed the system-imposed limit.
[EMFILE]
shmdt detaches the shared memory segment located at the
address specified by shmaddr from the calling process
data segment. [EINVAL]
shmdt will fail and not detach the shared memory
segment if shmaddr is not the data segment start
address of a shared memory segment. [EINVAL]
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Return Values
Upon successful completion, the return values are as
follows:
shmat returns the data segment start address of the
attached shared memory segment.
shmdt returns a value of 0.
Otherwise, a value of -1 is returned and errno is set to
indicate the error.
See Also
exec(S), exit(S), fork(S), intro(S), shmctl(S), shmget(S)
Notes
Programs using this function must be compiled with the -Me
compiler option.
For 286 processes, if a program is compiled using small or
middle model, the char far variables cannot be used as
arguments to the standard libc.a routines because these
routines require char near pointers. If the libc.a routines
are required, the program must be compiled using large or
huge model. If both the libc.a routines and small or middle
model compiling are required, the XENIX 3.0 shared data
system calls must be used.
Small data 386 processes must specify shmaddr equal to zero
(i.e. you must allow the system to attach the shared memory
segment at whatever address it chooses).
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