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include vmm.inc
 
mov     esi, OFFSET32 IdleCallback      ; points to callback procedure
VMMcall Call_When_Idle
 
jc      error                       ; carry set if callback not installed
 
The Call_When_Idle service installs a system-idle callback procedure. The
system calls this procedure whenever the Windows kernel signals that Windows
is idle and all other virtual machines are also idle. Virtual devices
typically use this service to perform background operations. For example,
the pageswap device uses this service to asynchronously write dirty pages to
the backing store.
 
Parameter     Description
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IdleCallback  Points to the callback procedure to install. See the Comments
              section for more information about the procedure.
 
Return Value
 
The carry flag is clear if the callback procedure is installed. Otherwise,
the carry flag is set.
 
Comments
 
Virtual devices can install any number of idle callback procedures. The
system calls each one, in the order installed, until one of the procedures
clears the carry flag.
 
The system calls each callback procedure as follows:
 
mov     ebx, SysVM          ; system VM handle
mov     ebp, OFFSET32 crs   ; points to a Client_Reg_Struc structure
call    [IdleCallback]
 
jc      pass_to_next        ; if carry set, call the next idle callback
 
 
The SysVM parameter specifies a handle identifying the system virtual
machine and the csr parameters points to a Client_Reg_Struc structure
containing the registers of the system virtual machine.
 
The callback procedure can carry out any operation and can modify EAX, EBX,
ECX, EDX, ESI, EDI, and Flags. If the operation takes a significant amount
of time, the procedure should clear the carry flag before returning to
prevent other callbacks from being called. Otherwise,  the procedure should
set the carry flag and return.
 
Uses
 
Flags
 
See Also
 
Call_When_Not_Critical, Call_When_Task_Switched
 
 
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