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References: <0f030e809f063f5a5e64ff7a7a0c3227 AT xs4all DOT nl> <20181216202847 DOT GK28727 AT calimero DOT vinschen DOT de>
In-Reply-To: <20181216202847.GK28727@calimero.vinschen.de>
From: Wayne Davison <wayne AT opencoder DOT net>
Date: Sun, 16 Dec 2018 13:36:10 -0800
Message-ID: <CAHSx_SvqFgi5stKvYSNCPwyyu98miPHyYcDKJL1-=KP8NE9+JQ@mail.gmail.com>
Subject: Re: /dev/fd/N not synonymous with file descriptor N; it is on Linux
To: cygwin <cygwin AT cygwin DOT com>
Content-Type: text/plain; charset="UTF-8"

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.

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.

> The way it's implemented in Cygwin uses the actual file path resolution and then either works or fails as above.

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 (note the dot-fd) before creating the normal
fd/0 symlink. Then, when a request came in to read /proc/$PID/fd/0, it
could check if the associated hard-link exists and read from that
instead.  Or perhaps the "symlink" info could be stored elsewhere and
the fd/0 file could be the hard-link, requiring the stat code to be
tweaked to look up the pretend-symlink info?

..wayne..

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