[plug] Productivity

[Carl Gherardi]

On 08/09/2004, at 1:18 PM, Cameron Patrick wrote:

> Rennie wrote:
>
>> Sounds very interesting. Could you please give us a quick summary of
>> what's going on - to save us the trouble of reading the hundreds of
>> emails - with this fascinating topic.
>>
I'll give this a go because i've been following the discussion with 
some interest. Disclaimer:This is my take on things not what is 
actually happening. This is a very long thread 2000+ emails so i'm 
going to miss plenty(and I dont claim to have read or understood all of 
them)

The linux kernel has a virtual file system layer, which defines what 
operations a filesystem can provide(write, read, link unlink etc) if it 
chooses to and its up to the filesystem on the implementation and 
whether it will support it.(eg. vfs defines write, but a cd filesystem 
has no need of it)

Reiser4 implements file operations that are not part of the vfs, and as 
such cant be implemented by other filesystems. The classic example of 
this is all files in reiser4 are also directories. Reiser4 has a plugin 
mechanism, which can completely change the way a file operates on a 
file by file basis. One could for example cd into a .tar.gz file(a file 
is a directory remember) using a reiser4 plugin, and possibly run 
make(!). Changing posix semantics for files was always going to be a 
flame war...

The files-are-directories semantics also cause difficult to solve 
locking issues(see http://kerneltrap.org/node/view/3749 for a technical 
description) There was an interesting mail on the list today about the 
difficulties in detecting loops in graphs also written by Al Viro

Theres been a lot of stuff about file streams, a revelation that 
copying a MS Word document to an ftp site and back down again loses 
some meta infomation, lots of people i've never seen post before 
arguing and generally a lot of bad blood flowing between several 
people. Somewhere in there there was also some reasonable technical 
discussions going on about kernel supported interfaces for meta 
information.

I found the lwn kernel article from last(week before?) on Reiser4 
pretty good aswell. That should be available to non-subscribers now.

For audiophiles out there Ingo Molnar has been doing a lot of work in 
reducing latencies in 2.6, and has most of the audio community happy 
now.

Cheers

Carl