Re: Switching from CVS to GIT

Johannes Schindelin [off-list ref] writes:

Hi,

On Mon, 15 Oct 2007, Eli Zaretskii wrote:

quoted

quoted

Date: Mon, 15 Oct 2007 00:45:47 +0100 (BST)
From: Johannes Schindelin <redacted>
cc: Alex Riesen <redacted>, ae@op5.se, tsuna@lrde.epita.fr, 
    git@vger.kernel.org, make-w32@gnu.org

The problem is not so much opening, but determining if an existing file 
and a file in the index have the same name.

For example, "README" in the index, but "readme" in the working directory, 
will be handled as "deleted/untracked" by the current machinery.  IOW git 
will not know that what it gets from readdir() as "readme" really is the 
same file as "README" in the index.

That's because you think file names are simple strings and can be
compared by simple string comparison.

Almost...

quoted

This na?ve view is not true even on POSIX systems: "foo/bar" and 
"/a/b/foo/bar" can be the same file, as well as "/a/b/c/d" and "/x/y/z", 
given the right symlinks.

... not quite, ah ...

quoted

But for some reason that eludes me, people who are accustomed to POSIX
stop right there and in effect say "file names are strings, if we only
make them absolute and resolve links".

... yes!  There you have it.  Absolute filenames, resolved by
readlink() are assumed to be the unique (!) identifiers for the
contents.

They aren't.  One can mount the same file system several times in
different places.  In Linux, one can even mount directories and files
to several places at once.  Most Unices also support some
case-insensitive file systems, and readlink does not canonicalize the
casing.

_Note:_ absolute paths _without_ readlink() resolving are _still_
unique identifiers; this time for files/symlinks.

Not even that.  A unique identifier for files would imply that
touching the file does not affect, say, the access times of files with
other unique identifiers.

-- 
David Kastrup