[phobos] Making std.stdio.readf @safe

[Jakub Łabaj via phobos]

There is an idea to make stdio.readf @trusted/@safe (reported 
here: https://issues.dlang.org/show_bug.cgi?id=8471). What 
currently makes it unsafe is LockingTextReader using functions 
FLOCK, FUNLOCK, FGETC (aliased from extern functions, dependent 
on the OS) and using a cast from 'shared(_IO_FILE)*' to 
'_IO_FILE*'.

I found out that stdio.write* functions are made @safe by 
declaring all methods of LockingTextWriter (similar to 
LockingTextReader) @trusted and using helper function:

/**
   * Property used by writeln/etc. so it can infer @safe since 
stdout is __gshared
*/
private @property File trustedStdout() @trusted
{
     return stdout;
}

So the obvious solution is to copy the approach of stdio.write. 
The other one would be to mark underlying functions 
FLOCK/FUNLOCK/FGETC @trusted (which in the process would allow to 
get rid off @trusted from LockingTextWriter, except casting from 
shared), but I'm not sure if it's legit as there may be some 
quirks and they should not be @trusted at all.

So my question are: are both solutions presented acceptable? If 
yes, which one is preferred? Or maybe there is a better one?