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Date: Sun, 16 Dec 2018 22:55:49 +0100
From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: /dev/fd/N not synonymous with file descriptor N; it is on Linux
Message-ID: <20181216215549.GO28727@calimero.vinschen.de>
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References: <0f030e809f063f5a5e64ff7a7a0c3227@xs4all.nl> <20181216202847.GK28727@calimero.vinschen.de> <CAHSx_SvqFgi5stKvYSNCPwyyu98miPHyYcDKJL1-=KP8NE9+JQ@mail.gmail.com>
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On Dec 16 13:36, Wayne Davison wrote:
> On Sun, Dec 16, 2018 at 12:29 PM Corinna Vinschen wrote:
> > In contrast to Linux the symlinks are not just faked symlinks with the =
underlying OS having direct access to the file descriptors.
>=20
> Yeah, Linux is more like a fuse where the open filehandles are used
> directly on open, and the stat calls return pretend symlinks with the
> lsof info.
>=20
> > The way it's implemented in Cygwin uses the actual file path resolution=
 and then either works or fails as above.
>=20
> If Cygwin can't be changed into a fuse idiom, perhaps a hard-link
> idiom could be used? For instance, when the /proc/$PID/fd/0 symlink is
> being created, the code could try to hard-link the file to
> /proc/$PID/.fd/0 first

Nice try, but hardlinks don't cross FS borders.  /proc is a filesystem
on its own with its own inode numbers.

I'm mulling over adding some hack to open().  It could try to recognize
the special case of opening a processes' own descriptor symlink within
/proc and then warp the open() call into dup().  No idea how tricky
or even feasible that is, though...


Corinna

--=20
Corinna Vinschen
Cygwin Maintainer

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