[PATCH] locks: rename file-private locks to file-description locks

[Rich Felker]

On Mon, Apr 21, 2014 at 04:23:54PM +0200, Michael Kerrisk (man-pages) wrote:
> On 04/21/2014 04:02 PM, Rich Felker wrote:
> > On Mon, Apr 21, 2014 at 09:45:35AM -0400, Jeff Layton wrote:
> >> File-private locks have been merged into Linux for v3.15, and *now*
> >> people are commenting that the name and macro definitions for the new
> >> file-private locks suck.
> >>
> >> ....and I can't even disagree. The names and command macros do suck.
> >>
> >> We're going to have to live with these for a long time, so it's
> >> important that we be happy with the names before we're stuck with them.
> >>
> >> The consensus on the lists so far is that they should be rechristened as
> >> "file-description locks".
> >>
> >> This patch makes the following changes that I think are necessary before
> >> v3.15 ships:
> >>
> >> 1) rename the command macros to their new names. These end up in the uapi
> >>    headers and so are part of the external-facing API. It turns out that
> >>    glibc doesn't actually use the fcntl.h uapi header, but it's hard to
> >>    be sure that something else won't. Changing it now is safest.
> >>
> >> 2) make the the /proc/locks output display these as type "FDLOCK"
> >>
> >> The rest of the renaming can wait until v3.16, since everything else
> >> isn't visible outside of the kernel.
> > 
> > I'm sorry I didn't chime in on this earlier, but I really prefer the
> > (somewhat bad) current naming ("private") to the
> > ridiculously-confusing use of "FD" to mean "file descriptION" when
> > everybody is used to it meaning "file descriptOR". The potential for
> > confusion that these are "file descriptOR locks" (they're not) is much
> > more of a problem, IMO, than the confusion about what "private" means
> > (since it doesn't have an established meaning in this context.
> > 
> > Thus my vote is for leaving things the way the kernel did it already.
> 
> There's at least two problems to solve here:
> 
> 1) "File private locks" is _meaningless_ as a term. Elsewhere

That's the benefit of it: it doesn't clash with any
already-established meaning. I agree it's less than ideal, but all the
alternatives I've seen so far are worse.

>    (http://thread.gmane.org/gmane.network.samba.internals/76414/focus=1685376),
>    I suggested various alternatives. "File-handle locks [*]" was my

This is also bad. "Handle" also has a defined meaning in POSIX. See
XSH 2.5.1:

http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html

>    initial preference, and I also suggested "file-description locks"
>    and noted the drawbacks of that term. I think it's insufficient
>    to say "stick with the existing poor name"--if you have
>    something better, then please propose it. (Note by the way
>    that for nearly a decade now, the open(2) man page has followed
>    POSIX in using the term "open file description. Full disclosure:
>    of course, I'm responsible for that change in the man page.)

I'm well aware of that. The problem is that the proposed API is using
the two-letter abbreviation FD, which ALWAYS means file descriptor and
NEVER means file description (in existing usage) to mean file
description. That's what's wrong.

> 2) The new API constants (F_SETLKP, F_SETLKPW, F_GETLKP) have names
>    that are visually very close to the traditional POSIX lock names 
>    (F_SETLK, F_SETLKW, F_GETLK). That's an accident waiting to happen
>    when someone mistypes in code and/or misses such a misttyping
>    when reading code. That really must be fixed.

I agree, but I don't think making it worse is a solution.

Rich