HP-UX Reference (11i v2 03/08) - 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.

Otherwise, 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

maximum 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’’.