Re: 'cp -lL' behaviour conflicts with documentation

[Eric Blake]

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According to Jim Meyering on 3/15/2005 10:35 AM:
> 
> But the actual referent (as opposed to the symlink value) may be
> another symlink, which may point to another, etc.  The final
> non-symlink value -- assuming there is one -- is the referent.
> It'd be easy if there were an flink syscall.  Then
> you'd just open the symlink (which would open the referent)
> and use flink to create a hard link to the file behind
> the descriptor.
> 
> Is it worth it to make cp manually follow a sequence of symlinks
> when given both -L and --link?

On a related matter, POSIX is a bit ambiguous about link utilities when
the source is a (nested) symlink.  For link(1), it defers strictly to
link(2), which does not directly mention what to do if path1 is a symlink.
 And for ln(1), step 3 states that link(2) should be called "using the
object that source_file references as the path1 argument", without saying
whether this must be the final referrent (or an error for broken links or
loops) or just a single dereference that might be another symlink.

Personally, I think that ln(1) should by default always try to resolve the
symlink down to a non-symlink file, and error out if that is not possible;
and that link(1) should be used to make hard links to symlinks on
architectures whose link(2) permit that.  Maybe it is also worth adding -H
- -L and -P to ln to bypass my proposed default, at the same time as fixing
cp -lL.

At any rate, the following sequence is a bug in ln(1), because it does not
involve any of the above-mentioned ambiguities:

$ uname
CYGWIN_NT-5.1
$ touch a
$ ln -s a b
$ ln b c      # Bug: c should be a hard link to a, not b
$ ls -l a b c
- -rw-r--r--  1 eblake None 0 Mar 15 19:04 a
lrwxrwxrwx  2 eblake None 1 Mar 15 19:04 b -> a
lrwxrwxrwx  2 eblake None 1 Mar 15 19:04 c -> a

- --
Life is short - so eat dessert first!

Eric Blake             address@hidden
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