linux-kernel - Re: [PATCH] locks: rename file-private locks to file-description locks

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Date:	Tue, 22 Apr 2014 06:54:36 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	"Stefan (metze) Metzmacher" <metze@...ba.org>,
	Jeff Layton <jlayton@...hat.com>
CC:	mtk.manpages@...il.com, Rich Felker <dalias@...c.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	samba-technical@...ts.samba.org,
	Ganesha NFS List <nfs-ganesha-devel@...ts.sourceforge.net>,
	Carlos O'Donell <carlos@...hat.com>,
	libc-alpha <libc-alpha@...rceware.org>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH] locks: rename file-private locks to file-description
 locks

On 04/21/2014 11:15 PM, Stefan (metze) Metzmacher wrote:
> Am 21.04.2014 21:55, schrieb Jeff Layton:
>> On Mon, 21 Apr 2014 21:39:12 +0200
>> "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> wrote:
>>
>>> On 04/21/2014 08:46 PM, Rich Felker wrote:
>>>> On Mon, Apr 21, 2014 at 08:32:44PM +0200, Michael Kerrisk (man-pages) wrote:
>>>>> On 04/21/2014 06:10 PM, Rich Felker wrote:
>>>>>> 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.
>>>>>
>>>>> So, can you *please* answer this question: what do you call (i.e., 
>>>>> what  everyday technical language term do use for) the thing
>>>>> that sits between a file descriptor and an i-node? 
>>>>>
>>>>> (Please don't say 'struct file' -- that is not is an implementation 
>>>>> detail, and does not qualify as the kind of term that I could use 
>>>>> when documenting this feature in man pages.)
>>>>
>>>> "Open file description".
>>>
>>> Oh! I didn't realize we agreed :-).
>>>
>>>>> POSIX uses (or invented, I am not sure which) the term file description
>>>>> for a good reason: it is unambiguous, and therefore precise. I do agree
>>>>> that there's a risk of confusion between 'open file descriptor" and 
>>>>> 'and file description'--it's the same kind of risk as between English 
>>>>> terms such as 'arbitrator' and 'arbitration' (and any number of other
>>>>> examples), and as language speakers we deal with this every day.
>>>>
>>>> There's not a problem when the full word is used. On the other hand,
>>>> if you use "arb" as an abbreviation for "arbitration" in a context
>>>> where it was already universally understood as meaning "arbitrator",
>>>> that would be a big problem.
>>>>
>>>> Likewise the problem here isn't that "open file description" is a bad
>>>> term. It's that using "FD" to mean "[open] file description" is
>>>> utterly confusing, even moreso than just making up a new completely
>>>> random word.
>>>
>>> Ohh -- I had thought you a problem not just with "FD" but also
>>> "(open) file description".
>>>
>>>>>>> 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.
>>>>>
>>>>> I don't agree that it's making it worse. The real problem here is 
>>>>> that people use no good unambiguous term for the thing between a file
>>>>> descriptor and an inode. POSIX provides us with a solution that may
>>>>> not seem perfect, but it is unambiguous, and I think it might feel
>>>>> more comfortable if we used it often enough.
>>>>
>>>> I would like to see it used more too, and in particular, I think it
>>>> belongs in the documentation for these new locking interfaces. But
>>>> that still doesn't answer the question of what to call them (the
>>>> macros) unless you want:
>>>>
>>>> F_OPEN_FILE_DESCRIPTION_GETLK
>>>> F_OPEN_FILE_DESCRIPTION_SETLK
>>>> F_OPEN_FILE_DESCRIPTION_SETLKW
>>>
>>> Or just 'F_OFD_*'?
>>>
>>>> Perhaps "OP" (for open-private, i.e. private to the particular open)
>>>> would be a sensible choice; OTOH people are likely to misread it as
>>>> OPeration. The general principle I have in mind though is that it
>>>> might be nice to highlight the word "open" in "open file description"
>>>
>>> (Fair enough.)
>>>
>>>> since it (1) contrasts with file descriptor, despite file descriptors
>>>> also dealing with open files, and (2) contrasts well with legacy fcntl
>>>> locks, which are (this is the whole bug) associated with the
>>>> underlying file and not the open file description.
>>>
>>> Makes sense to me. (We are in more agreement that I realized.)
>>>
>>> Cheers,
>>>
>>> Michael
>>>
>>>
>>>
>>
>> So the motion is to call them "open file description locks" and change
>> the macros to read *_OFD_*. Does anyone object?
> 
> Works fine for me...

And works for me.


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