[sane-devel] Proposal to change function signatures of a couple of sanei_usb_* functions

[Ralph Little]

Hi,
I'm having a go at writing my first SANE backend for a learning exercise.

I notice that a few backends that use the functions: 
sanei_usb_attach_matching_devices() and sanei_usb_find_devices() require 
some context information in the callback function to complete the find 
function.
This is typically because the backend is looping through a list of known 
device configurations and calling the sanei_* function on each one: the 
callback needs to know the element in that loop to complete the attach 
function in the callback.

This is typically achieved with setting some global variables to be 
picked up by the callback function, or searching again through the 
original loop using information gleaned from the devicename (such as 
vendor and product), both of which are messy and ugly hacks.

I propose that we change the function signature of the functions and the 
callback to include a (void *) context pointer:

SANE_Status
sanei_usb_find_devices (SANE_Int vendor, SANE_Int product, void *context,
             SANE_Status (*attach) (SANE_String_Const dev, void *context));

void
sanei_usb_attach_matching_devices (const char *name, void *context,
                    SANE_Status (*attach) (const char *dev, void *context));

I would have to change existing backends that rely on this function but 
I feel that it would be an improvement and clean up the processing of 
USB device detection.

Comments?

Cheers,
Ralph