Question about file system permissions

[Joe Smith]

Les Mikesell wrote:
> On Tue, 2007-01-02 at 14:17 -0500, Joe Smith wrote:
>> Mikkel L. Ellertson wrote:
>>> .... But as you have
>>> noticed, it does not work out as well when editing shared files.
>> Oddly perhaps, Unix has never really provided shared writeable files. 
> 
> What?  If you have write permission you can write.

But two processes writing to the same file at the same time gives you 
what? Probably not what you want.

I don't mean literally Unix can't do it, I only meant that Unix never 
really supported it with a standard API that worked well enough to be 
widely accepted and handled all the complicated corner cases that rear 
up when two users want to naively "share a file".

>> Perhaps there are good theoretical reasons for it; perhaps it was just 
>> one of those simplifying assumptions that Unix was born with, I don't know.
> 
> Initially there was no file locking and the only really atomic
> operation was creating a file or making a hard link to an existing
> file.  Later, about a dozen different file locking methods were
> added and the applications never really converged on how to do
> it across versions and network mounts.  Plus, a lot of stuff depends
> on the unix filesystem semantics ...

Thanks for making my point with real facts ;-)

Sorry everybody: drifting off-topic and talking stuff that I know just 
well enough to make an ass of myself, so I'm going to shut up right 
about... now.

<Joe