From: Fabrice Popineau <fabrice.popineau@gmail.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: Emacs developers <emacs-devel@gnu.org>
Subject: Re: w32.c/link()
Date: Mon, 16 Jun 2014 20:48:14 +0200 [thread overview]
Message-ID: <CAFgFV9Na8NXa6Vb+A+675+RWaijkYSX=bKS4Pdtm6FEwcTnJpg@mail.gmail.com> (raw)
In-Reply-To: <CAFgFV9OXfoGKxD6TWsbiraiHyR2xqt2DD3eYJaN5WRn9=MXqpQ@mail.gmail.com>
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I have found my problem.
I did what Eli said and it is working as expected.
But now I start again :
emacs -Q
M-: (add-name-to-file "c:/temp/foo.el" "c:/temp/foo1.el" t)
M-x c:/temp/foo.el
add a few characters
C-x s
M-x dired
And foo.el size has changed, but not foo1.el size.
This is because after editing foo.el, foo1.el is still a hard link but to
foo.el~ (autosave file). :-/
Quite misleading! Sorry for the noise.
Fabrice
2014-06-16 19:55 GMT+02:00 Fabrice Popineau <fabrice.popineau@gmail.com>:
> Thanks for the explanations.
> After carefully trying again, it is working as expected.
>
> Fabrice
>
>
> 2014-06-16 16:55 GMT+02:00 Eli Zaretskii <eliz@gnu.org>:
>
> > From: Fabrice Popineau <fabrice.popineau@gmail.com>
>> > Date: Mon, 16 Jun 2014 07:30:50 +0000 (UTC)
>> >
>> > I tried to use add-name-to-file from elisp,
>> > which calls w32.c/link(). It seems to end up in doing
>> > a copy of the file.
>>
>> No, it doesn't copy. It creates a hard link, as you'd expect.
>>
>> You can verify this yourself, with the following simple procedure:
>>
>> . start Dired on some directory
>> . go to any file in the listing (not a directory: Windows doesn't
>> support hard links to directories)
>> . notice that the second column from the left says "1", i.e. this
>> file has only 1 link to its data
>> . press H, type the name of a link in the minibuffer and press RET
>> . press g to refresh the directory listing, and notice that both the
>> original file and the link now have their link count at 2
>> . visit the original file, set backup-by-copying-when-linked to a
>> non-nil value, then modify the file and save it
>> . visit the link and observe that the same modifications are
>> "miraculously" present there as well
>> . still not convinced? type "C-u C-x d", change the switches to say
>> "-ali", hit RET, and observe that both the file and the link have
>> the same filesystem index (a.k.a. "inode"), which means they share
>> the same file data
>>
>> If you have a decent port of GNU 'ls', you will see the link counts
>> change there as well.
>>
>> If you see something different from the above, please describe what
>> you see.
>>
>> > I'm fine with that, but that wasn't clear before trying it.
>> > OTOH if hard links were possible, why not using them? Permissions?
>>
>> We do use them (on NTFS; on other Windows filesystems you'll likely
>> get an error).
>>
>> > Could someone (Eli ?) care to explain why link() is implemented this
>> way?
>> > Why BackupWrite() is used? I would have expected either CopyFile() or
>> > CreateHardLink().
>>
>> CreateHardLink was introduced with Windows 2000, while this code tries
>> to support older NT systems which lacked that API. Back then this was
>> the only way to create a hard link. I don't think we still support
>> NT4 etc., but the code works very well, so I see no reason to rewrite
>> it using newer APIs.
>>
>
>
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next prev parent reply other threads:[~2014-06-16 18:48 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-16 7:30 w32.c/link() Fabrice Popineau
2014-06-16 14:55 ` w32.c/link() Eli Zaretskii
2014-06-16 17:55 ` w32.c/link() Fabrice Popineau
2014-06-16 18:48 ` Fabrice Popineau [this message]
2014-06-16 19:27 ` w32.c/link() Eli Zaretskii
2014-06-16 20:58 ` w32.c/link() Stefan Monnier
2014-06-16 22:08 ` w32.c/link() Fabrice Popineau
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