Mandatory File Locking

[test test]

Yeah it should work supposedly but its not working. For reference I'm
attaching a sample file may be I am doing something very wrong.
I make executable of attached code. Then run one instance on terminal & 2nd
on another terminal.
Executable on 2nd terminal is able to write in the file.


Regards,
~Nishant

On Sat, Nov 22, 2008 at 12:56 AM, Mark Haney <mhaney at ercbroadband.org>wrote:

> test test wrote:
> > Hello,
> >
> >
> >
> > I need to put a mandatory lock on /dev/fb0 (presently any file) in Linux
> OS.
> > But in actual scenario it will be a device file.
> >
> >
> >
> > OS: Ubuntu Hardy Heron 8.04
> >
> >
> >
> > Scenario:
> >
> > 1. Process A is super process (controller).
> >
> > 2. Process B is normal process.
> >
> > 3. *Process A and B are non-cooperating process, they simple don't know
> > about other process existence and they are not interested in knowing it
> > either.(So, advisory locking is out of scope). *
> >
> > 4. At particular instance Process B is accessing /dev/fb0.
> >
> > 5. Now, Process A wants access to it.
> >
> > 6. Process A locks /dev/fb0
> >
> > 7. It can hold the lock as long it wants & in any case process B cannot
> > write anything to it. (It's better if B cannot read the contents also).
> >
> >
> >
> > I also changed permissions of directory and lock file.
> >
> >
> >
> > I used:
> >
> > chmod g-x test
> >
> > chmod g+s test
> >
> >
>
> http://www.hackinglinuxexposed.com/articles/20030623.html
>
> That was a quick google on file locking in Linux.  Are you coding these
> processes yourself?  I mean there are documented ways of locking files
> programmatically in linux as well.
>
> Based on what you posted the file locking should work.  Are you saying
> it doesn't?
>
>
>
>
>
> --
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>
> Mark Haney
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>
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