|SHMGET(2)||FreeBSD System Calls Manual||SHMGET(2)|
NAMEshmget — obtain a shared memory identifier
LIBRARYStandard C Library (libc, -lc)
SYNOPSIS#include < sys/types.h>
#include < sys/ipc.h>
#include < sys/shm.h>
shmget( key_t key, size_t size, int flag);
DESCRIPTIONBased on the values of key and flag, shmget() returns the identifier of a newly created or previously existing shared memory segment. The key is analogous to a filename: it provides a handle that names an IPC object. There are three ways to specify a key:
- IPC_PRIVATE may be specified, in which case a new IPC object will be created.
- An integer constant may be specified. If no IPC object corresponding to key is specified and the IPC_CREAT bit is set in flag, a new one will be created.
- The ftok(3) may be used to generate a key from a pathname.
The mode of a newly created IPC object is determined by OR'ing the following constants into the flag argument:
- Read access for owner.
- Write access for owner.
- Read access for group.
- Write access for group.
- Read access for other.
- Write access for other.
When creating a new shared memory segment, size indicates the desired size of the new segment in bytes. The size of the segment may be rounded up to a multiple convenient to the kernel (i.e., the page size).
RETURN VALUESUpon successful completion, shmget() returns the positive integer identifier of a shared memory segment. Otherwise, -1 is returned and errno set to indicate the error.
ERRORSThe shmget() system call will fail if:
- [ EINVAL]
- Size specified is greater than the size of the previously existing segment. Size specified is less than the system imposed minimum, or greater than the system imposed maximum.
- [ ENOENT]
- No shared memory segment was found matching key, and IPC_CREAT was not specified.
- [ ENOSPC]
- The kernel was unable to allocate enough memory to satisfy the request.
- [ EEXIST]
- IPC_CREAT and IPC_EXCL were specified, and a shared memory segment corresponding to key already exists.
|December 17, 2010||FreeBSD|