VH-VE SHM

VH-VE SHM is a feature for VE programs to register System V shared memory created at VH side to DMAATB of VE. More...

Functions
int	vh_shmget (key_t key, size_t size, int shmflag)
	This function gets the identifier of system V shared memory on VH. More...
void *	vh_shmat (int shmid, const void *shmaddr, int shmflag, void **vehva)
	This function attaches system V shared memory on VH and register it with DMAATB. More...
int	vh_shmdt (const void *shmaddr)
	This function detaches system V shared memory on VH and releases DMAATB entry. More...

Detailed Description

VH-VE SHM is a feature for VE programs to register System V shared memory created at VH side to DMAATB of VE.

Please include "vhshm.h".

Note

VH-VE SHM feature does not provide a function to create System V shared memory. A user program at VH side needs to create System V shared memory.

System V shared memory needs to be created with SHM_HUGETLB flag to allocate huge pages (2MB pages). The kernel parameter "vm.nr_hugepages" needs to be set, in order to allocate huge pages.

1. Check whether "vm.nr_hugepages" exists in /etc/sysctl.conf and files under /etc/sysctl.d and /usr/lib/sysctl.d.
2. If "vm.nr_hugepages" does not exists, add "vm.nr_hugepages = 4096" to /etc/sysctl.conf. 4096 is tentative value. Please set required value for your program.
3. If "vm.nr_hugepages" exists, add the required value to the current value of "vm.nr_hugepages"
4. Execute "sysctl --system" command

VE programs can use VE DMA feature to transfer data between System V shared memory and VE memory registered to DMAATB.

Function Documentation

int vh_shmget	(	key_t	key,
		size_t	size,
		int	shmflag
	)

This function gets the identifier of system V shared memory on VH.

Note

Argument is similar to shmget(2). Different points are shown below.

If a specified size is smaller than actual shared memory size, actual shared memory size is used.

Invoking this function is not required if the program knows the shared memory identifier.

Parameters

[in]	key	A key value associated with System V shared memory segment on VH. Don't specify IPC_PRIVATE.
[in]	size	Size of System V shared memory segment on VH
[in]	shmflag	SHM_HUGETLB must be specified. Don't specify SHM_NORESERVE IPC_EXCL and IPC_CREAT.

Returns

A valid shared memory identifier on Success, -1 on Failure.

• EINVAL SHM_HUGETLB is not specified as 3rd argument. SHM_NORESERVE or IPC_EXCL or IPC_CREAT are specified as 3rd argument.
• EINVAL IPC_PRIVATE is specified as 1st argument.
• EINVAL A segment with given key existed, but size is greater than the size of the segment.
• EACCES The user does not have permission to access the shared memory segment, and does not have the CAP_IPC_OWNER capability.
• ENOENT No segment exists for the given key.

void* vh_shmat	(	int	shmid,
		const void *	shmaddr,
		int	shmflag,
		void **	vehva
	)

This function attaches system V shared memory on VH and register it with DMAATB.

Note

Argument is similar to shmat(2). Different points are shown below.

On Linux, it is possible to attach a shared memory segment even if it is already marked to be deleted. vh_shmat() follows it.

Parameters

[in]	shmid	System V shared memory segment identifier.
[in]	shmaddr	This argument must be NULL.
[in]	shmflag	SHM_RDONLY can be specified. Don't specify SHM_EXEC, SHM_REMAP and SHM_RND.
[in]	vehva	An address of pointer to store VEHVA.

Returns

A valid shared memory identifier on Success, (void *)-1 on Failure.

• EINVAL shmaddr is not NULL.
• EINVAL SHM_EXEC, SHM_REMAP or SHM_RND are specified.
• EINVAL Invalid shmid value.
• EFAULT vehva is invalid or the specified segment is not huge page.
• ENOMEM Can't allocate DMAATB more. No enough memory at VH side.
• ECANCELED Failed to update resource information (VEOS internal error).
• EACCES The calling process does not have the required permissions for the requested attach type, and does not have the CAP_IPC_OWNER capability.
• ENOTSUP VEOS does not connect to IVED.
• EIDRM shmid points to a removed identifier.

int vh_shmdt

(

const void *

shmaddr

)

This function detaches system V shared memory on VH and releases DMAATB entry.

Parameters

[in]

shmaddr

An address which is attached to System V shared memory on VH

Returns

0 on Success, -1 on Failure.

• ECANCELED Failed to update resource information (VEOS internal error).
• EINVAL shmaddr is invalid. There is no shared memory segment attached at shmaddr, or shmaddr is not aligned on a page boundary.