Install_IO_Handler

include vmm.inc

mov esi, IOCallback ; points to callback procedure

mov edx, Port ; I/O port number

VMMcall Install_IO_Handler

jc not_installed ; carry flag set if procedure not installed

The Install_IO_Handler service installs a callback procedure for I/O port trapping, and enables trapping for the specified port. Only one procedure may be installed for a given port.

This service is only available during initialization.

Parameters

IOCallback

Points to the callback procedure. For more information about the callback procedure, see the following “Comments” section.

Port

Specifies the I/O port to be trapped.

Return Value

The carry flag is clear if the service successfully installs the callback procedure. If the carry flag is set, a callback procedure is already installed for the specified port or the system limit for I/O callback procedures has been reached.

Comments

The system calls the callback procedure whenever a program in a virtual machine attempts to access the specified I/O port, and I/O trapping is enabled. The system calls the procedure as follows:

mov ebx, VM ; current VM handle

mov ecx, IOType ; type of I/O

mov edx, Port ; port number

mov ebp, OFFSET32 crs ; points to a Client_Reg_Struc

mov eax, Data ; output data (if I/O type is output)

call [IOCallback]

mov [Data], eax ; input data (if I/O type is input)

The VM parameter specifies the current virtual machine, the Port parameter specifies the I/O port, and the crs parameter points to a Client_Reg_Struc structure containing the register contents for the current virtual machine.

The IOType parameter specifies the type of input or output operation requested and determines whether the callback procedure receives data in the EAX register or must return data in the EAX register. The IOType parameter can be a combination of the following values:

Value

Meaning

Addr_32_IO	Use 32-bit address offsets for input or output string operations. If this value is not given, the 16-bit offsets are used.
Byte_Input	Input a single byte; place in AL if String_IO not given.
Byte_Output	Output a single byte from AL if String_IO not given.
Dword_Input	Input a double word; place in EAX if String_IO not given.
Dword_Output	Output a double word from EAX if String_IO not given.
Rep_IO	Repeat the input or output string operation the number of times specified by the Client_CX field in the Client_Reg_Struc structure.
Reverse_IO	Decrement string address on each input or output operation. If this value is not given, the string address is incremented on each operation.
String_IO	Input or output a string. The high 16-bits specifies segment address of buffer containing the string to output or to receive the string input.
Word_Input	Input a word; place in AX if String_IO not given.
Word_Output	Output a word from AX if String_IO not given.

The Data parameter is used only for when I/O type is for output.

A virtual machine can disable trapping of a port for every or for specific
virtual machines by using the Disable_Global_Trapping and
Disable_Local_Trapping services.

Uses

Flags