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
Date: Sun, 16 Dec 2018 20:31:00 -0000 [thread overview]
Message-ID: <20181216203118.GL28727@calimero.vinschen.de> (raw)
In-Reply-To: <20181216202847.GK28727@calimero.vinschen.de>
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On Dec 16 21:28, Corinna Vinschen wrote:
> On Dec 16 17:31, Houder wrote:
> > L.S.,
> >
> > /dev/fd/N not synonymous with file descriptor N; it is on Linux
>
> Yes, it is. Most of the time. Try this:
>
> $ echo foo | cat /dev/fd/0
>
> The problem is that some of the concepts don't work as desired:
>
> > 64-@@ cat /dev/fd/0 <<\EOF
>
> If you observe what happens in tcsh in this situation you see that it
> doesn't even execute cat as long as you didn't type EOF. What you type
> is written to a tmpfile:
>
> $ ls -l /proc/5980/fd
> total 0
> lrwxrwxrwx 1 corinna vinschen 0 Dec 16 21:15 0 -> /tmp/sh.lVQq04
> lrwxrwxrwx 1 corinna vinschen 0 Dec 16 21:15 15 -> /dev/pty0
> lrwxrwxrwx 1 corinna vinschen 0 Dec 16 21:15 16 -> /dev/pty0
> lrwxrwxrwx 1 corinna vinschen 0 Dec 16 21:15 17 -> /dev/pty0
> lrwxrwxrwx 1 corinna vinschen 0 Dec 16 21:15 18 -> /dev/pty0
> lrwxrwxrwx 1 corinna vinschen 0 Dec 16 21:15 19 -> /dev/pty0
>
> However, this tmpfile has been unlinked already, so it has been moved to the
> recycle bin:
>
> $ ls -l /tmp/sh.lVQq04
> ls: /tmp/sh.lVQq04: No such file or directory
>
> So the path in the fd subdir doesn't reflect the actual file path.
>
> But after starting cat, cat tries to open /proc/self/fd/0 which
> is in fact the non-existing path /tmp/sh.lVQq04. Bad luck.
>
> In contrast to Linux the symlinks are not just faked symlinks with the
> underlying OS having direct access to the file descriptors. The way
> it's implemented in Cygwin uses the actual file path resolution and then
> either works or fails as above. I'm not sure how to fix that easily.
> I guess the fd/0 symlink would have to show the actual file path pointing
> to the recycle bin. But that's often not what you want either since it
> hows a patch outside the POSIX namespace.
shows a path
Sorry,
Corinna
--
Corinna Vinschen
Cygwin Maintainer
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next prev parent reply other threads:[~2018-12-16 20:31 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-16 16:31 Houder
2018-12-16 20:28 ` Corinna Vinschen
2018-12-16 20:31 ` Corinna Vinschen [this message]
2018-12-16 21:36 ` Wayne Davison
2018-12-16 21:55 ` Corinna Vinschen
2018-12-17 4:30 ` Houder
2018-12-17 9:25 ` Corinna Vinschen
2018-12-17 11:26 ` Corinna Vinschen
2019-01-02 13:56 ` Houder
2018-12-17 3:41 ` Houder
2019-01-06 20:19 ` Corinna Vinschen
2019-01-22 8:50 ` Houder
2019-01-22 8:57 ` Houder
2019-01-22 9:06 ` Corinna Vinschen
2019-01-22 9:25 ` Houder
2019-01-22 9:42 ` Corinna Vinschen
2019-01-22 10:20 ` Houder
2019-01-22 10:39 ` Corinna Vinschen
2019-01-27 18:39 ` Houder
2019-01-27 21:57 ` Corinna Vinschen
2019-01-27 22:12 ` Corinna Vinschen
2019-01-28 14:15 ` Houder
2019-01-28 16:51 ` Corinna Vinschen
2019-01-22 9:02 ` Corinna Vinschen
2019-01-22 9:07 ` Corinna Vinschen
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