How to get all commands defined in a specified file (or files)?

[mbork]

Hi all,

say that I'd like to define a `execute-extended-command' alternative
which would only allow to run commands defined in a specified file.  How
can I get all such commands?  I know about `symbol-file', but I don't
know how it works (and it's complicated enough that I'm not sure I want
to study it ATM;-) - I tried to instrument it for edebug, but a quick
run revealed only that it's pretty mysterious).  I also looked at the
property plist of a function name and saw that the filename is not kept
there.  Any hints?

TIA,

-- 
Marcin Borkowski
https://mbork.pl
https://crimsonelevendelightpetrichor.net/