Re: dup2() vs dup3() inconsistency when

[H. Peter Anvin]

Michael Kerrisk wrote:
> Al,
>
> your 2008-07-26 commit 6c5d0512a091480c9f981162227fdb1c9d70e555 for
> fs/fcntl.c:sys_dup3 contains
>
> +       if (unlikely(oldfd == newfd))
> +               return -EINVAL;
>
> This makes dup2() and dup3() differ with respect to the oldfd==newfd
> case (dup2() becomes a no-op, just returning oldfd, dup3() gives the
> EINVAL error.
>
> Your commit log doesn't explain the rationale for this change.  What
> is it?  (I could guess that it is to error on a case that may be a
> user programming error, but I want to check this with you, so that I
> add the right text to the man page.)

The dup2() behavior comes from the logical consequence of dup2()'s 
"close on reuse"; one would think it would be logical for dup3() to 
behave the same way.

	-hpa
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