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Date: Thu, 09 Mar 2017 11:13:49 -0800
From: L A Walsh <cygwin AT tlinx DOT org>
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To: cygwin AT cygwin DOT com
Subject: Re: Treating Junctions consistently, as "normal dirs" as w/linux "bind"-type mount
References: <58A4741E DOT 5020408 AT gmail DOT com> <20170216092611 DOT GE3889 AT calimero DOT vinschen DOT de> <58B0AA58 DOT 30504 AT tlinx DOT org> <20170228214321 DOT GB13542 AT calimero DOT vinschen DOT de> <58C0D744 DOT 2030005 AT tlinx DOT org> <1599023500 DOT 20170309163724 AT yandex DOT ru> <58C1795B DOT 5010809 AT tlinx DOT org> <20170309164113 DOT GC7716 AT calimero DOT vinschen DOT de>
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Corinna Vinschen wrote:
> He's right. The mount point handling in Cygwin is based on the
> in-memory mount table.  
----
    I'm not wanting a mount point fake.  Just wanting it to look
like a normal dir just like the mountvol-junctions.

> There's no reasonable way to fake some
> reparse point to look like a mount point.  We can either handle it
> as normal dir, or as symlink.  Handling it as normal dir is 
> problematic in terms of find/rsync
----
    T All of the core utils are loop-protected in that respect.
same-dev file systems already exist on linux and cygwin.

    File system loops are already present just using mountvol:

>  mountvol
...
\\?\Volume{578b2172-f917-11e4-b3d9-a0369f15ce28}\
        C:\mountedVol\
/mountedVol> mkdir remounted

# note, next "2" lines are really 1 wrapped line:

/mountedVol> mountvol remounted  
'\\?\Volume{578b2172-f917-11e4-b3d9-a0369f15ce28}\'


So the same volume is mounted at C:\mountedVol and at
C:\mountedVol\remounted.
>  etc, bacause the cross-device
> check would fail and files are potentially visited multiple times.
>   
----
That isn't what happens right now with mountvol:

find shows:

/> find mountedVol/ -type d
mountedVol/
mountedVol/$RECYCLE.BIN
mountedVol/$RECYCLE.BIN/S-1-5-21-1885695451-752926663-1105222378-1000
mountedVol/$RECYCLE.BIN/S-1-5-21-1885695451-752926663-1105222378-1025
mountedVol/$RECYCLE.BIN/S-1-5-21-1885695451-752926663-1105222378-500
mountedVol/$RECYCLE.BIN/S-1-5-21-33333-77777-33333-5013
find: File system loop detected; ‘mountedVol/remounted’ is part of the 
same file system loop as ‘mountedVol/’.
mountedVol/System Volume Information

I.e. 'find' (and other coreutils) detect the loop even though
they are the same file system.

Sure, you can find program(s) that are broken and don't detect
such loops, but at least the core utils do check -- and besides,
no one HAS to create junctions -- they can use symlinks as they do
today and no risk of such problems.

But treating linkd-junctions the same as mountvol-junctions allows
those bind-style mounts that are supported on linux and Windows
to be supported on Cygwin.


   

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