Re: [PATCH] open: introduce O_NOSTD

Davide Libenzi
2009-08-25T21:53:54Z

On Tue, 25 Aug 2009, Eric Blake wrote:

> Another solution is for the application to sanitize all newly-created
> fds: GNU coreutils provides a wrapper open_safer, which does nothing
> extra in the common case that open() returned 3 or larger, but calls
> fcntl(n,F_DUPFD,3)/close(n) before returning if n was less than 3.
> However, this leads to triple the syscall cost for every open() call
> if the process starts life with a std fd closed; and if O_CLOEXEC is
> not used, still leaves a window of time where the fd can be leaked
> through another thread's use of fork/exec.

I think we can say that the vast majority of the software is not going to
notice the proposed open_safer(), performance-wise, since the first three
fds are always filled. So IMO the performance impact argument is a weak one.
If CLOEXEC semantics are needed in the open operation, F_DUPFD_CLOEXEC can
be used to match it.
While the patch is simple, IMO this is something that can be easily taken
care in glibc layers w/out huge drawbacks.

- Davide