This is the mail archive of the cygwin mailing list for the Cygwin project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: {lp,cb}Reserved2 under Windows 7 and file descriptors

On Thu, Jul 15, 2010 at 12:25:09PM +0100, Andy Koppe wrote:
>On 15 July 2010 09:19, Corinna Vinschen wrote:
>>> Furthermore, there is a very long-standing issue with Cygwin pty devices:
>>> while Cygwin programs report true from isatty() when called on a Cygwin PTY,
>>> MSVCRT applications do *not*.
>> Right.
>>> [...]
>>> However, due to the way the CRT works, we can fool it into thinking a
>>> passed-in file descriptor is actually a tty. All you need to do is use 3 for
>>> the value of *lpReserved2, then follow it with three flag bytes, then three
>>> HANDLE values --- corresponding respectively to flags[fd0], flags[fd1],
>>> flags[fd2] and fh[0], fh[fd1] and fh[fd2]. ??This information would be
>>> followed by the normal child_info structure. If stdin, stdout, or stderr is
>>> a Cygwin PTY, Cygwin can manually set the FDEV bit (described in the old
>>> MSDOS headers) in corresponding flag byte, which will make _isatty() return
>>> true in the child.
>>> (Not that I've actually tried it --- it's just an idea.)
>> That sounds like an interesting idea. ??I'll play around with it as soon
>> as I have a bit of spare time again. ??Unless, of course, nobody else
>> will try it or already did...
>It would be brilliant if this did work, taking at least some of the
>sting out of the whole pty vs interactive console app issue.

I actually have thought about doing this in the past but it always
seemed to me that lying to a program about the "ttyness" of a file
handle was going to cause more subtle problems than what we have

It also obviously isn't a panacea since not everything is going to use
msvcrt file handles.

If we really can create a standard file handle structure and not have to
tweak it for the next five years and if we only fill it out for
non-cygwin programs (which we do know when we're about to exec
something) maybe it will be worth it.  I think I'm going to need some
real convincing though.

Hmm.  I wonder if anything else does this.  Does MKS do something similar?


Problem reports:
Unsubscribe info:

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]