HP OpenVMS systems documentation

The interface for the MMG_STD$IOLOCK routine is:

int mmg_std$iolock (void *buf, int bufsiz, int is_read, PCB *pcb, void **svapte_p)

This routine returns a 32-bit address by reference (the svapte_p parameter) which, depending on the routine status, may specify the address of the first PTE or the address of a location in the buffer that must be faulted in.

The new version of this routine must accept a 64-bit buffer address. In addition, the new version must also return either a 64-bit PTE or buffer address. This is an incompatible interface change because this return parameter is passed by reference. Thus, MMG_STD$IOLOCK has been removed and is replaced by the new MMG_STD$IOLOCK_BUF routine.

The interface for MMG_STD$IOLOCK_BUF is:

int mmg_std$iolock_buf (VOID_PQ const buf, const int bufsiz, const int is_read, PCB *const pcb, PTE_PPQ va_pte_p, VOID **fault_va_p)

Table B-14 summarizes the use of the arguments.

Table B-14 MMG_STD$IOLOCK_BUF Arguments

Argument	Type	Access	Description
buf	VOID_PQ	Input	64-bit pointer to the buffer that is to be locked.
bufsiz	int	Input	Size of the buffer in bytes.
is_read	int	Input	Contains the value 0 if buffer will be only written to the device, 1 if the buffer will be only read from device, 5 if the buffer will be modified by the device.
pcb	PCB *	Input	Pointer to the process PCB.
va_pte_p	PTE_PPQ	Output	Pointer to a 64-bit PTE address that is returned. If the returned value of the function is successful, then the address returned is the 64-bit virtual address of the first PTE that maps the buffer. For all other function return values, the value returned in this parameter is undefined.
fault_va_p	VOID_PPQ	Output	Pointer to a 64-bit address that is returned. If the returned value of the function is zero, then the address returned is the 64-bit address within the buffer that must be faulted in. For all other function return values, the value returned in this parameter is undefined.

The returned value of this routine is a system condition value or the value zero:

	Success	A successful VMS condition value indicates that the buffer has been locked and that the 64-bit virtual address of the first PTE that maps the buffer has been returned using the va_pte_p parameter.
	0	This return value means that a page fault is required for a page in the buffer. The virtual address of the page is returned using the fault_va_p parameter. Any portion of the buffer that may have been locked before this condition was detected has been unlocked before returning.
	Failure	Standard VMS condition value that indicates the failure.

Just like MMG_STD$IOLOCK, the MMG_STD$IOLOCK_BUF routine must be called in process context at IPL 2 and it acquires and releases the MMG spinlock.

Although the interfaces for the MMG_STD$IOLOCK_BUF and MMG_STD$IOLOCK routines are similar, there are important differences between these routines that go beyond the width of the address parameters.

1. The 32-bit address that is returned by MMG_STD$IOLOCK in the svapte_p parameter is valid regardless of process context. In contrast, the 64-bit address that is returned by MMG_STD$IOLOCK_BUF in the va_pte_p parameter may be valid only in the context of the current process. The new routines IOC_STD$FILL_DIOBM and IOC_STD$CREATE_DIOBM are designed to deal with this difference.
2. The MMG_STD$IOLOCK routine locks into memory the level-3 page tables that contain the PTEs that map the buffer as well as the buffer pages. In contrast, MMG_STD$IOLOCK_BUF only locks the buffer pages. It does not lock the level-3 page tables because it would be difficult to unlock them in the absence of process context where MMG_STD$IOUNLOCK_BUF is called. Moreover, the mechanisms used by IOC_STD$FILL_DIOBM and IOC_STD$CREATE_DIOBM usually do not require the locking of the level-3 page tables. Only when the PTE window method is used by IOC_STD$FILL_DIOBM or IOC_STD$CREATE_DIOBM will these routines need to lock the level-3 page table pages into memory. When this case applies, the IOC_STD$RELEASE_DIOBM routine has enough information to unlock the level-3 page tables regardless of process context.

The existing callers of MMG_STD$IOLOCK need to be very aware of the first of these differences. The second difference is likely to be transparent to most callers.

Because the routine MMG$IOLOCK is simply a JSB-to-CALL jacket routine around MMG_STD$IOLOCK, the MMG$IOLOCK routine has also been removed.

B.17.1 CALL_IOLOCK Macro

The CALL_IOLOCK MACRO-32 macro facilitates the use of the MMG_STD$IOLOCK routine by code that was originally written to use the JSB-interface counterpart MMG$IOLOCK. The CALL_IOLOCK macro has implicit register inputs and outputs that correspond to the register inputs and outputs of the JSB-interface for the MMG$IOLOCK routine.

Because this macro uses registers for its inputs and outputs, it can be altered to use the full 64-bit values in these registers and it can call the MMG_STD$IOLOCK_BUF routine instead of MMG_STD$IOLOCK. Nevertheless, the CALL_IOLOCK macro has been modified to generate a suppressable interface warning at compile-time, because:

• The full 64-bits of register R1 are now significant on return.
• The returned PTE address is a 64-bit process virtual address.
• Callers of MMG_STD$IOLOCK_BUF are very likely to need to call the new IOC_STD$FILL_DIOBM or IOC_STD$CREATE_DIOBM routines.

The format of the macro call is:

CALL_IOLOCK [ INTERFACE_WARNING=YES|NO ]

By default the interface warning is enabled and generates the following warning at compile-time:

%AMAC-W-GENWARN, generated WARNING: 0 CALL_IOLOCK interface has changed for 64-bit virtual addressing; set INTERFACE_WARNING=NO to disable messages. %AMAC-W-GENWARN, generated WARNING: 0 CALL_IOLOCK uses the 64-bit buffer address in R0 %AMAC-W-GENWARN, generated WARNING: 0 CALL_IOLOCK returns a 64-bit VA_PTE or fault VA in R1 %AMAC-W-GENWARN, generated WARNING: 0 CALL_IOLOCK does not lock the page table pages %AMAC-W-GENWARN, generated WARNING: 0 A call to IOC_STD$FILL_DIOBM may be required to derive a SVAPTE

The compile-time warning serves to identify the existing callers of this macro. Once the invoking code has been modified, the warning can be suppressed by specifying INTERFACE_WARNING=NO.

B.18 MMG_STD$UNLOCK, MMG$UNLOCK, MMG_STD$IOUNLOCK_BUF

The interface for the MMG_STD$UNLOCK routine is:

void mmg_std$unlock (int npages, void *svapte)

The MMG$UNLOCK routine is simply a JSB-to-CALL jacket routine around MMG_STD$UNLOCK.

Because 32-bit PTE addresses that may point to PTE copies are sufficient for the needs of the MMG_STD$UNLOCK routine, there is no absolute requirement to change the interface of these routines. However, it is extremely likely that all callers of MMG_STD$UNLOCK and MMG$UNLOCK need to use the new DIOBM structure and need to call the new routine IOC_STD$RELEASE_DIOBM immediately after unlocking the memory buffer. Therefore, routine MMG_STD$UNLOCK has been renamed to MMG_STD$IOUNLOCK_BUF and the MMG$UNLOCK routine has been removed in order to make it difficult to miss the places where this source change is needed.

The interface for MMG_STD$IOUNLOCK_BUF is:

void mmg_std$iounlock_buf (const int npages, PTE_PQ const va_pte);

Just like MMG_STD$UNLOCK, the MMG_STD$IOUNLOCK_BUF routine does not depend on process context. However, the IPL and spinlocks of the caller must allow this routine to acquire and restore the MMG spinlock.