GNU bug report logs - #25814
Windows same_file macro is not reliable

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Kees Dekker <Kees.Dekker <at> infor.com>
To: "bug-diffutils <at> gnu.org" <bug-diffutils <at> gnu.org>
Subject: Windows same_file macro is not reliable
Date: Mon, 20 Feb 2017 16:01:09 +0000

[Message part 1 (text/plain, inline)]

Hi,

On file systems that do not support inodes (e.g. NTFS, because not everything is POSIX), the same_file() macro (in system.h) is incorrect as st_ino (and probably st_dev) are meaningless. See also https://msdn.microsoft.com/en- us/library/14h5k7ff.aspx<https://msdn.microsoft.com/en-%20us/library/14h5k7ff.aspx>. I would suggest to add an #ifdef _WIN32 macro that let return same_file() 0.

The same applies to same_file_attributes macro. The st_uid and st_gid fields are never set to a useful value on Windows (see MSDN URL as mentioned before).

The resulting suggested code would be:

#if _WIN32
# define same_file(s, t) 0
#else
# define same_file(s, t) \
    ((((s)->st_ino == (t)->st_ino) && ((s)->st_dev == (t)->st_dev)) \
     || same_special_file (s, t))
#endif

and

#ifndef same_file_attributes
#if _WIN32
# define same_file_attributes(s, t) 0
#else
# define same_file_attributes(s, t) \
   ((s)->st_mode == (t)->st_mode \
    && (s)->st_nlink == (t)->st_nlink \
    && (s)->st_uid == (t)->st_uid \
    && (s)->st_gid == (t)->st_gid \
    && (s)->st_size == (t)->st_size \
    && (s)->st_mtime == (t)->st_mtime \
    && (s)->st_ctime == (t)->st_ctime)
#endif
#endif

Since I'm unfamiliar with git, please check whether this change is feasible.

Regards,
Kees

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