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Re: file locking

2000-08-16 16:29:07
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Hi there

On Wed, 16 Aug 2000 guenther+procmail(_at_)gac(_dot_)edu wrote:

Xander Soldaat <xander(_at_)soldaat(_dot_)com> writes:
I was wondering if it is necessary to use the :0: flag when writing to a 
file,
 ie something like this:
:0:
* some_condition
my_file

I was using procmail with VERBOSE=yes defined in my rc file and I
noticed some thing about aquiring kernel locks. Does this mean that the
":" is not always necessary, but only in the case of using a program
such as formail to write something to a file?

If you can trust the kernel-locking (no NFS involved, etc), and _all_
programs that access the file use kernel locking, then "yes".
Otherwise, no.
But who is to say that the other programs will respect the lock file :) If the 
kernel has put a lock on a file, does this mean that the file cannot be opened 
in RW mode? I am not much of a programmer anymore, but this would be 
interesting to see. If this were the case then surely kernel locking would be a 
far superior method for local filesystems.
The lock file mechanism is just user-space, is it not? Another program would 
have to know that the lock file in the cwd belongs to file "A" and not file "B".

Just wondering...
Xander

- --------------------------------------------------------------------
Xander Soldaat                                    xander(_at_)soldaat(_dot_)com
Firewall/security consultant                      xander(_at_)competa(_dot_)com

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