On 08/04/2021 10:04, Marvin Häuser wrote:
Thank you a lot. One thing I noticed is that part of the quote I did not
see on the list before, so I marked it below.
On 08.04.21 00:10, Andrew Fish wrote:
The general UEFI (and UEFI PI) is we mostly add new things, and don’t
depreciated things to maintain compatibility. So for example you can
add a new Protocol to a handle so you have V1 and V2 of a protocol on
the same handle. An example of this is SimpleTextIn and
SimpleTextInEx. SimpleTextIn was modeled on the LCD of a serial
terminal (our server roots) so it did not expose modifier keys, or
have an easy way to implement snag keys so that is why SimpleTextInEx
got added for the new functional.
^ Here; +1
The addition of EFI_SIMPLE_TEXT_INPUT_EX_PROTOCOL was really not a good
example of how to handle this issue gracefully.
Here is the kind of workaround that external code has to implement: it's
a perfect example of how this "add a V2 protocol" approach ends up
imposing a permanent maintenance burden on external code:
https://github.com/ipxe/ipxe/commit/a08244ecc
Note that there was absolutely no reason for the specification to
require a V2 protocol in order to support Ctrl-<key>, and the EDK2
codebase will indeed do the sensible thing and return the ASCII values
for Ctrl-<key> via the original EFI_SIMPLE_TEXT_INPUT_PROTOCOL. It
would be amazing if, as you suggested, everyone uses the EDK2 codebase
and so all public implementations of EFI_SIMPLE_TEXT_INPUT_PROTOCOL
would do this sensible thing.
Unfortunately, this is not the case. Very large numbers of vendors use
some other non-EDK2 implementation that does not do the sensible thing.
I have no idea why.
It's also worth noting that the addition of
EFI_SIMPLE_TEXT_INPUT_EX_PROTOCOL opened up a gaping potential security
hole related to pointer lifetimes, as documented in the above-linked
commit message.
TL;DR: please assume that creating a V2 protocol has a very significant
cost, and needs to come with benefits that outweigh that very
significant cost. If you can achieve what you need without breaking
backwards compatibility, then that represents a massive increase in value.
Thanks,
Michael
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