The serial ops used a legacy calling convention that passed in just the
pointer to the userdata pointer (ie the first argument to the functions
was "void **userdata").
That's actually very inconvenient, because the custom IO data can not
only contain other interesting information that was filled in by the
custom IO provider, it also made it harder to chain these things
together, as exemplified by the core to emulate serial over the packet
interface in the subsurface bluetooth code.
This also adds the 'dc_context_t' field that is passed to the packet
routine open. That can allow the open routine to override the
'custom_io' details of the context at open time (to allow nested
custom_io operation).
Note that callers of the open function need to be aware that the
'custom_io' can be changed by the act of opening a custom_io, and the
value shouldn't be cached in some local variable.
Finally, this adds a new user-supplied opaque pointer
dc_user_device_t *user_device;
to the custom_io descriptor.
The 'user_device' data is filled in when registering the custom_io with
data that the custom IO open() routines can use. This is different from
the existing 'userdata' in that the 'user_device' is filled in before
dc_open_device() is called (and "open" can then use it to limit what
kinds of devices it looks for, for example).
In contrast, the existing 'userdata' field is filled in by the
"xyz_open()" routines, and contains the data necessary for the IO
itself.
The SSRF_CUSTOM_IO define is updated to v2 to indicate the new
interfaces.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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