HP-UX Reference (11i v3 07/02) - 2 System Calls (vol 5)

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shmget(2) shmget(2)

System V Shared Memory Under Adaptive Address Space

Itanium-based platforms have the capability to create two types of processes: MGAS (Mostly Global

Address Space), which is the default, and MPAS (Mostly Private Address Space). See ld(1) and chatr(1).

If 64-bit MPAS and 64-bit MGAS processes want to share a mapping among themselves without incurring

the cost of aliasing, then (shmﬂg &

IPC_GLOBAL ) should be "true", but (shmﬂg &

IPC_SHARE32 ) should

be "false". 64-bit MPAS processes should also specify the

IPC_GLOBAL ﬂag to the shmat(2) call. Such a

mapping cannot be shared with 32-bit MGAS processes.

See the Adaptive Address Space Whitepaper for details.

EXAMPLES

The following call to

shmget() returns a unique shmid for the newly created shared memory segment of

4096 bytes:

int myshmid;

myshmid = shmget (IPC_PRIVATE, 4096, 0600);

RETURN VALUE

Upon successful completion, a non-negative integer, namely a shared memory identiﬁer, is returned. Oth-

erwise, a value of −1 is returned and errno is set to indicate the error.

ERRORS

shmget() fails if any of the following conditions are encountered:

[EINVAL] size is less than the system-imposed minimum or greater than the system-imposed

maximum.

[EINVAL] A shared memory identiﬁer exists for key but is in 64-bit address space and the pro-

cess performing the request has been compiled as a 32-bit executable. In order to

avoid receiving this error, both

IPC_SHARE32 and IPC_CREAT must be set in

shmﬂg by the 64-bit processes upon segment creation.

[EACCES] A shared memory identiﬁer exists for key but operation permission (see glossary(9)) as

speciﬁed by the low-order 9 bits of shmﬂg would not be granted.

[EINVAL] A shared memory identiﬁer exists for key but the size of the segment associated with

it is less than size and size is not equal to zero.

[ENOENT] A shared memory identiﬁer does not exist for key and (shmﬂg &

IPC_CREAT)is

"false".

[ENOSPC] A shared memory identiﬁer is to be created but the system-imposed limit on the max-

imum number of allowed shared memory identiﬁers system wide would be exceeded.

[ENOMEM] A shared memory identiﬁer and associated shared memory segment are to be created,

but the amount of available physical memory is not sufﬁcient to ﬁll the request.

[ENOMEM] A shared memory segment with

IPC_CREAT or IPC_GLOBAL

speciﬁed was to be

created; however, there is not enough space in the global quadrant.

[EEXIST] A shared memory identiﬁer exists for key but ((shmﬂg &

IPC_CREAT)&&(shmﬂg &

IPC_EXCL) ) is "true".