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 : > Thanks for the explanations. > After carefully trying again, it is working as expected. > > Fabrice > > > 2014-06-16 16:55 GMT+02:00 Eli Zaretskii : > > > From: Fabrice Popineau >> > 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. >> > >