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Date: Mon, 18 Dec 2023 13:04:00 +0100
Message-ID: <CALXu0Ue9SyJod+0k24pQzs3KPg1RPquRfhN3tw3GYG-qMt_+DQ@mail.gmail.com>
Subject: Re: Cygwin generates syscalls for *.lnk files on filesystems with
 native symlink support?
To: cygwin AT cygwin DOT com
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From: Cedric Blancher via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Cedric Blancher <cedric DOT blancher AT gmail DOT com>
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Sender: "Cygwin" <cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com>

On Fri, 1 Sept 2023 at 13:00, Corinna Vinschen via Cygwin
<cygwin AT cygwin DOT com> wrote:
>
> On Sep  1 06:23, Cedric Blancher via Cygwin wrote:
> > Good morning!
> >
> > During a Cygwin 3.4.8-1.x86_64 debugging session I noticed something
> > odd when I looked at the network traffic generated by one of our
> > cluster nodes:
> > It seems that for each call to a tool (i.e. starting "sed" from
> > "bash") Cygwin searches for *.lnk files.
> >
> > Is this correct even when the filesystem in question has native
> > symlink support (e.g. NFS)?
>
> Yes.  During file handling, Cygwin doesn't know what filesystem a
> file is on until it could actually open the file and request file
> and filesystem info from the open handle.

Why? If you have the path name you could lookup the (cached) mount
points, and determine the filesystem type. Same solution applies for
UNC paths, where you can easily lookup the filesystem type, and cache
it per-process or in Cygserver.

> So if Cygwin couldn't open
> "foo" because the NtCreateFile call returned with status
> STATUS_OBJECT_PATH_NOT_FOUND or STATUS_OBJECT_NAME_NOT_FOUND, or
> STATUS_NO_SUCH_FILE, or one of the countless other status codes the
> kernel (or the driver) might return in case a file doesn't exist,
> it will tack on .lnk and .exe and, for historical reasons, .exe.lnk,
> and try again.

Can this machinery please be turned off via CYGWIN env var option? As
discussed in https://www.mail-archive.com/cygwin AT cygwin DOT com/msg174547.html
this machinery causes very bad filesystem lookup performance, and it
would IMO a good idea to have an option to turn this off, and just
allow and expect native links (for NTFS, ReFS and NFS). Maybe CYGWIN
env var option winsymlinks_expect:native? winsymlinks_expect takes a :
seperated list which symlink types are to be expected.

Ced
-- 
Cedric Blancher <cedric DOT blancher AT gmail DOT com>
[https://plus.google.com/u/0/+CedricBlancher/]
Institute Pasteur

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