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

[Hans Reiser <reiser@xxxxxxxxxxx>]

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