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List:       freebsd-hackers
Subject:    Re: locking revisited
From:       Garance A Drosihn <drosih () rpi ! edu>
Date:       1999-08-30 15:40:40
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At 12:52 PM +0930 8/28/99, Greg Lehey wrote:
>FreeBSD is one of the few operating systems which doesn't have
>kernel-level locking.  If we want to emulate other systems correctly,
>we *must* have advisory locking.  This includes SCO UNIX, System V.4
>and Linux.  I suspect it also includes Microsoft.
>
>All this doesn't leave too much room for arguments about whether
>locking works or not: it works on all platforms except FreeBSD, and
>that's only because FreeBSD doesn't implement locking.

I agree (for what it's worth)

>As a result, I argue that we should implement locking.  The questions
>are: how?  I'd suggest three ...  [the third being:]
>
> - Via separate calls to fcntl.  fcntl currently has the following
>   command values:
>
>     #define	F_DUPFD		0   /* duplicate file descriptor */
>     #define	F_GETFD		1   /* get file descriptor flags */
>     #define	F_SETFD		2   /* set file descriptor flags */
>     #define	F_GETFL		3   /* get file status flags */
>     #define	F_SETFL		4   /* set file status flags */
>     #define	F_GETOWN	5   /* get SIGIO/SIGURG proc/pgrp */
>     #define   F_SETOWN	6   /* set SIGIO/SIGURG proc/pgrp */
>     #define	F_GETLK		7   /* get record locking information */
>     #define	F_SETLK		8   /* set record locking information */
>     #define	F_SETLKW	9   /* F_SETLK; wait if blocked */
>
>   We could add a F_SETMANDLOCK or some such.
>
>Any thoughts?

On this last option, I assume that means a program could open
some file, set this option, and then other programs would behave
as if the mandatory-locking flag was on for that file.  However,
that behavior would only last as long as the first program, the
one which set the option, still had the file-descriptor open?

Presumably this new fcntl value would only be honored for
programs executing as the owner of the file?  (or some other
limited group, to limit denial-of-service attacks)


---
Garance Alistair Drosehn           =   gad@eclipse.acs.rpi.edu
Senior Systems Programmer          or  drosih@rpi.edu
Rensselaer Polytechnic Institute


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