Re: [RFC][glibc PATCH] fcntl-linux.h: add new definitions and manual updates for open file description locks

["Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>]

On Wed, Apr 23, 2014 at 9:00 PM, Alfred M. Szmidt <ams@gnu.org> wrote:
>    > Likewise.  You infact write that it does get the lock information
>    > later in the document wrt. F_OFD_GETLK.
>
>    Sorry, I disagree here...GETLK is really a misnomer, IMO. TESTLK
>    would have been a better name.

I'm inclined to agree.

>    GETLK are used is to "get the first lock".
>
>    It's a way to test whether a particular lock can be applied, and to
>    return information about a conflicting lock if it can't. If, for
>    instance there is no conflicting lock, then you don't "get" any
>    lock information back (l_type just gets reset to F_UNLCK).
>
> While I kinda see your point, it isn't what GETLK does; it really does
> get you information about the first lock -- you're not testing
> anything.  It is also the terminology used in the POSIX standard.

The POSIX wording is a little confused. For example, what does "first"
mean in this context? F_GETLK returns information about one
(arbitrarily selected) lock that blocks a lock you would like to
place. So, I'm inclined to agree with Jeff -- this really is a "test"
(or "can I lock it") operation.

Of course, the operation has no reliable use: by the time it returns
the information might already be out of date. I suspect that it was
designed to solve the problem: "My F_GETLK operation failed. Who's
blocking me?"

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/