Re: fix off-by-one in dup2

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

On Wed, Dec 04, 2013 at 06:23:24PM +0100, Corinna Vinschen wrote:
>On Dec  4 12:00, Christopher Faylor wrote:
>> On Wed, Dec 04, 2013 at 01:04:08PM +0100, Corinna Vinschen wrote:
>> >On Dec  4 12:36, Corinna Vinschen wrote:
>> >> On Dec  4 10:32, Corinna Vinschen wrote:
>> >> > Hi guys,
>> >> > [...etc...]
>> >> > The problem is still present in the current sources.
>> >> > [...]
>> >
>> >Ouch, ouch, ouch!  I tested the wrong DLL.  Actually current CVS fixes
>> >this problem.  Duh.  Sorry for the confusion.
>> >
>> >One question, though.  Assuming start is == size, then the current code
>> >in CVS extends the fd table by only 1.  If that happens often, the
>> >current code would have to call ccalloc/memcpy/cfree a lot.  Wouldn't
>> >it in fact be better to extend always by at least NOFILE_INCR, and to
>> >extend by (1 + start - size) only if start is > size + NOFILE_INCR?
>> >Something like
>> >
>> >  size_t extendby = (start >= size + NOFILE_INCR) ? 1 + start - size : NOFILE_INCR;
>> >
>> >?
>> >
>> >Sorry again.  Fortunately it's my WJM week...
>> 
>> I don't think it is a common occurrence for start >= size.  It is
>> usually done when something like bash dup2's stdin/stdout/stderr to a
>> high fd.  Howeer, I'll check in something which guarantees that there is
>> always a NOFILE_INCR entries free after start.
>
>That might be helpful.  Tcsh, for instance, always dup's it's std
>descriptors to the new fds 15-19.  If it does so in this order, it would
>have to call extend 5 times.

dtable.h:#define NOFILE_INCR    32

It shouldn't extend in that scenario.  The table starts with 32
elements.

cgf