SHMAT(2) | System Calls Manual | SHMAT(2) |
shmat
, shmdt
—
#include <sys/shm.h>
void *
shmat
(int
shmid, const void
*shmaddr, int
shmflg);
int
shmdt
(const
void *shmaddr);
shmat
() maps the shared memory segment associated with
the shared memory identifier shmid into the address
space of the calling process. The address at which the segment is mapped is
determined by the shmaddr parameter. If it is equal to
0, the system will pick an address itself. Otherwise, an attempt is made to
map the shared memory segment at the address shmaddr
specifies. If SHM_RND
is set in
shmflg, the system will round the address down to a
multiple of SHMLBA
bytes
(SHMLBA
is defined in
<sys/shm.h>
).
A shared memory segment can be mapped read-only by specifying the
SHM_RDONLY
flag in shmflg.
shmdt
() unmaps the shared memory segment
that is currently mapped at shmaddr from the calling
process' address space. shmaddr must be a value
returned by a prior shmat
() call. A shared memory
segment will remain in existence until it is removed by a call to
shmctl(2) with the
IPC_RMID
command.
shmat
() returns the address at which the shared memory
segment has been mapped into the calling process' address space when
successful, shmdt
() returns 0 on successful
completion. Otherwise, a value of -1 is returned, and the global variable
errno is set to indicate the error.
shmat
() will fail if:
EACCES
]ENOMEM
]EINVAL
]shmaddr specifies an illegal address.
EMFILE
]shmdt
() will fail if:
EINVAL
]shmat
and shmdt
system calls
conform to X/Open System Interfaces and Headers
Issue 5 (“XSH5”).
June 17, 2002 | NetBSD 9.2 |