DrvEscape

The DrvEscape function is used for retrieving information from a device that is not available in a device-independent device driver interface; the particular query depends on the value of the iEsc parameter.

ULONG
  DrvEscape(
    IN SURFOBJ  *pso,
    IN ULONG  iEsc,
    IN ULONG  cjIn,
    IN PVOID  pvIn,
    IN ULONG  cjOut,
    OUT PVOID  pvOut
    );

Parameters

pso

Pointer to a SURFOBJ structure that describes the surface to which the call is directed.

iEsc

Specifies a query. The meaning of the other parameters depends on this value. QUERYESCSUPPORT is the only predefined value; it queries whether the driver supports a particular escape function. In this case, pvIn points to an escape function number; cjOut and pvOut are ignored. If the specified function is supported, the return value is nonzero.

cjIn

Specifies the size, in bytes, of the buffer pointed to by pvIn.

pvIn

Pointer to the input data for the call. The format of the input data depends on the query specified by the iEsc parameter.

cjOut

Specifies the size, in bytes, of the buffer pointed to by pvOut.

pvOut

Pointer to the output buffer. The format of the output data depends on the query specified by the iEsc parameter.

Return Value

The return value is dependent on the query specified by the iEsc parameter. If the function specified in the query is not supported, the return value is zero.

Headers

Declared in winddi.h. Include winddi.h.

Comments

Drawing on the device is not allowed in this function. DrvDrawEscape is to be used for specialized drawing support.

GDI passes data directly from a (possibly malicious) client application to the driver, which means that the DrvEscape function must validate all input arguments. Specifically, this function must:

• Verify that the value received in the iEsc parameter represents a valid query.
• Verify that the size of the input buffer (the value in the cjIn parameter) is valid for the specified query.
• Verify that the contents of the buffer pointed to by the pvIn parameter are valid for the specified query.
• Verify that the size of the specified output buffer (the value in the cjOut parameter) is valid for the specified query.

Microsoft reserves the range 0 to 0X10000 for its escape codes. Third-party vendors are free to choose escape codes for their own use above this range. Since driver-specific escape codes may conflict with those used in other display drivers, it is important for a display driver to validate escape parameters before processing the escape. One way to do this would be to validate the input and output block sizes and the input block parameters. For added security, drivers should also include a "magic" value which must be set appropriately in every input block to ensure that the input block is from a trusted source.

DrvEscape is optional for all drivers.

See Also

DrvDrawEscape, SURFOBJ