fork/exec & close file descriptors

[Alain Ketterlin]

random832 at fastmail.us writes:

> On Wed, Jun 3, 2015, at 03:11, Alain Ketterlin wrote:
>> Thank you, I know this. What I mean is: what are the reasons that you
>> cannot access your file descriptors one by one? To me closing a range of
>> descriptors has absolutely no meaning, simply because ranges have no
>> meaning for file descriptors (they're not ordered in any way). What if
>> some library uses its own descriptors that happen to lie in your
>> "range"? Etc.
>
> The context in which this is useful is that you've just forked, and
> you're about to exec. "Some library" isn't going to ever get back
> control within the current process.

Any decent library will (on linux) use close-on-exec, or even have
fini/dtor functions to clean up. Any that does not is buggy. But of
course, if you shoot in their feet...

> Generally the range of file descriptors you want to close is (e.g.)
> 3-Infinity, after you've already got 0 1 and 2 pointing to where you
> want them (whatever redirected file or pipe).

Closing 3-... is meaningless, probably useless, and potentially harmful.

-- Alain.