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Re: reiser4 (was Re: [PATCH] Revised extended attributes interface)

To: Andrew Pimlott <andrew@xxxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: reiser4 (was Re: [PATCH] Revised extended attributes interface)
From: Hans Reiser <reiser@xxxxxxxxxxx>
Date: Thu, 13 Dec 2001 23:47:01 +0300
Cc: Anton Altaparmakov <aia21@xxxxxxxxx>, Nathan Scott <nathans@xxxxxxx>, Andreas Gruenbacher <ag@xxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, linux-xfs@xxxxxxxxxxx
References: <20011205143209.C44610@wobbly.melbourne.sgi.com> <20011207202036.J2274@redhat.com> <20011208155841.A56289@wobbly.melbourne.sgi.com> <3C127551.90305@namesys.com> <20011211134213.G70201@wobbly.melbourne.sgi.com> <5.1.0.14.2.20011211184721.04adc9d0@pop.cus.cam.ac.uk> <3C1678ED.8090805@namesys.com> <20011212204333.A4017@pimlott.ne.mediaone.net> <3C1873A2.1060702@namesys.com> <20011213102729.B3812@pimlott.ne.mediaone.net>
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Andrew Pimlott wrote:

On Thu, Dec 13, 2001 at 12:23:46PM +0300, Hans Reiser wrote:

Andrew Pimlott wrote:

First, I write a desktop application that wants to save an HTML file
along with some other object that contains the name of the creating
application.  The latter can go anywhere you want, except in the
same stream as the HTML file.  The user has requested that the
filename be /home/user/foo.html , and expects to be able to FTP this
file to his ISP with a standard FTP program.  What calls does my
application make to store the HTML and the application name?  If the
answer is different depending on whether /home/user is NTFS or
reiserfs4, explain both ways.

Are you sure that standard ftp will be able to handle extended attributes without modification?


No, the ftp program only needs to transfer the HTML part.

One approach is to create a plugin called ..archive that when read is a virtual file consisting of an archive of everything in the directory.


Ok, does this mean that every directory in the filesystem (or in some part of it) will automatically have a node ..archive? Presumably, it will not appear in directory listings, but can be read but not written to? Does this mean that a legacy application (pathological as it may be) that expects to be able to create a file called ..archive will fail?

I remember that I used to be a sysadmin with some NetApp boxes that have a .snapshot directory that is invisible, and has special qualities.

It worked.  There were no namespace collision problems.  None.

These things can be survived by users.;-)

Nothing I say should be construed to mean that I think that a particular name for a pseudo-file implemented by the default regular directory plugin is what should ship. I am easy in such matters. You can also get me to agree it should be modifiable, so that if Joe Sevenpack needs a file named ..archive, he can have it.



Or do you mean that the application would explicitly create the node
associated with this plugin?

Both. If you want a file named '..glob' that does the same thing as
'..archive', go for it. I am not necessarily committed to putting ..archive in the default directory plugin (actually, I don't like that name, it should be something snappier, but I haven't thought of it). I also am not funded to implement ..archive at the moment (I am funded to do inheritance though) .




It would be interesting I think to attach said plugin to standard directories by default along with several other standard plugins like ..cat, etc.


Anyway, you didn't answer the part I really care about. What calls does the application make to store the HTML and the "extended attribute"? You can pick whatever conventions you want, just give me an example.


read, write, etc., on file.html/..joes_attribute, unless it is a particular attribute that has particular effects on the particular plugin for file.html, in which case it all depends on the plugin and the constraints imposed on joes_attribute. It may be that modifying file.html modifies ..joes_attribute as a side-effect, plugins can do anything in response to a VFS operation. You put the plugin into your kernel, you'd better be able to trust it....




Second, I booted NT and created a directory in the NTFS filesystem
called /foo .  In the directory, I created a file called bar.  I
also created a named stream called bar, and an extended attribute
called bar.  Now I boot Linux.  What calls do I make to see each of
the three objects called bar?

You access /foo/bar, /foo/bar/,,bar, /foo/..bar by name.


How do I access the file called ..bar (created in NT) in the directory /foo?


If you have permission, you can: cat /foo/..bar

Or you can use the efficient for small files API we are implementing, which I won't go into here.



(Anton, does NTFS define any reserved filename characters, or only
win32?)

Andrew






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