Fun_People Archive
2 Mar
Microsoft invents symbolic links!

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From: Peter Langston <psl>
Date: Thu,  2 Mar 100 11:55:02 -0800
To: Fun_People
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Subject: Microsoft invents symbolic links!

X-Lib-of-Cong-ISSN: 1098-7649  -=[ Fun_People ]=-
From: Dan Franklin

This is from

     Microsoft Research Innovations Enhance Windows 2000

     REDMOND, Wash., Feb. 28, 2000 -- Three years ago, Bill Bolosky and
     two Microsoft colleagues were brainstorming technology advances when
     an idea occurred to them -- why not save operating system disk space
     by storing duplicate files as links that point to a single file housed
     in a central location?

     Not only would this save storage space, they reasoned; it would also
     result in substantial performance improvements. Moreover, it would
     make it faster for information technology (IT) managers to install
     computers for new employees since they'd no longer be required to
     copy massive amounts of data each time they set up a new desktop.

Symbolic links, as described in the first paragraph, can be traced back at
least as far as Multics (i.e., between 25 and 35 years ago). UNIX symbolic
links are modelled on the ones in Multics.

The use of network file systems and symbolic links to reduce administrative
copying, as described in the 2nd paragraph, has been used by Sun virtually
since the inception of NFS.  Maybe Apollo did it before them.

The one innovation seems to be the creation of a filesystem, the Single
Instance Store, that identifies identical files automatically via
signatures, removes the extra copies, and creates copy-on-write links for
them.  I'm sure this will work perfectly.

Not discussed in the article is the implementation of symlinks itself - a
not-so-new notion called "reparse points" by Microsoft.  Instead of
embedding symlinks into your filesystem, you embed specially identified
executable code that the kernel calls to determine the rest of the
filename.  This is much more general than symlinks, and is obviously better
because of all the advantages:

1. Harder to detect loops
2. A very nice security hole for attackers
3. If the reparse code has a bug, you can crash the whole OS
4. OS version incompatibilities can be embedded in shared filesystems -
better upgrade EVERYBODY to win2k, guys!

and, best of all,

5. They STILL haven't implemented symlinks.  That is, according to my
informant, there is no tool that just inserts a "reparse point" to point to
another place in the filesystem.  Unless it's in the NT Resource Kit for
Win2k; he hasn't found it yet, but you never know.

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