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include vmm.inc VMMcall _SetFreePhysRegCalBk, <Callback, flags> or eax, eax ; nonzero if installed, zero if error jz not_installed |
The _SetFreePhysRegCalBk service installs a callback procedure for managing the free list for a free physical region. The system calls the callback procedure whenever the memory manager puts a page on the free list or wants to obtain a physical page.
Any number of callback procedures can be installed.
This service is only available during initialization.
Callback
Points to the callback procedure to install. For more information about the callback procedure, see the following “Comments” section.
flags
Specifies the operation flags. This parameter must be set to 0.
The EAX register contains a nonzero value if the service is successful. Otherwise, EAX contains zero to indicate an error such as insufficient memory to define the callback procedure.
When the system places a page on the free list, the system gives a callback
procedure the option to take the page and map it in a free physical region using
the _MapFreePhysReg service. When the system needs a page, the system requests pages from the callback procedures. They provide pages by using the _UnmapFreePhysReg service to unmap the pages from the free physical region, and put it back on the free list.
The system calls the callback procedure as follows:
mov eax, Request ; 0 for pages available, 1 for pages needed
mov ecx, Pages ; count of pages available or needed
call [Callback]
jc dont_chain ; carry flag set if request satisfied
The Request parameter specifies whether the call is a notification of free pages or a request for free pages. This parameter is 0 if the pages are available, and 1 if the pages are needed. All other values are reserved.
The Pages parameter specifies the count of page either currently available in the free list, or requested by the memory manager to be placed on the free list.
The callback procedure sets the carry flag to indicate that it carried out the request, and to prevent the system from calling the next callback procedure in the chain. If the callback procedure cannot complete the entire request, it must clear the carry flag.
The callback procedure can modify all registers except the segment registers and the EBP register.
If more than one callback procedure is installed, the system calls each procedure in the chain unless a procedure returns with the carry flag set. The system varies the order in which it calls the procedures, ensuring that every procedure is periodically the first to be called.
When Request is 1, the callback procedure must release pages for regions which were mapped without the PageFixed value.
The callback procedure must release all free physical region pages which were mapped without the PageFixed value.
The callback procedure can release more pages than requested. The extra pages remain on the free list until the next operation places pages on the free list. At this point, the system sends a notification (Request is 0) to the callback procedure for all of the pages currently on the free list.
In general, a callback procedure should not call any services other than the _MapFreePhysReg and _UnmapFreePhysReg services. Calling other services, particularly nonasynchronous services, may cause the system to be re-entered.
The system does not begin calling the free-physical-region callback procedures until after the Init_Complete message has been processed by all virtual devices.
EAX