This would leave room to have either 1 or 2 blanks before things like function or class definitions, which IMO should be fixed to either 1 (I just used 1 because our code base does more or less that) or 2 (as for instance pep8 enforces for python). What I would not do is to leave it up to the contributor, I'd rather have some uniformity

Fair concern. We could use this set of configurations for that then:

# The number of newlines before a function prototype.
nl_before_func_body_proto       = 0        # unsigned number

# The number of newlines before a multi-line function definition.
nl_before_func_body_def         = 0        # unsigned number

# The number of newlines before a class constructor/destructor prototype.
nl_before_func_class_proto      = 0        # unsigned number

# The number of newlines before a class constructor/destructor definition.
nl_before_func_class_def        = 0        # unsigned number

This was more a suggestion than a request (that's why I only commented).

I agree with your opinion, but we should take into account our whole code base, since this is the file for all the code in the eProsima repositories.

I haven't checked all of them, but I think you are right that we are almost always using a single blank line everywhere.

Yes, definitely! That's why I'd like as many opinions as possible here