Package: coreutils;
Reported by: Gian Piero Carrubba <gpiero <at> rm-rf.it>
Date: Mon, 4 Nov 2013 23:38:02 UTC
Severity: wishlist
Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):
From: Gian Piero Carrubba <gpiero <at> rm-rf.it> To: bug-coreutils <at> gnu.org Subject: [cp] -R modifies dereferencing settings Date: Tue, 5 Nov 2013 00:37:06 +0100
[Message part 1 (text/plain, inline)]
Severity: wishlist
Please Cc: me as I'm not subscribed.
POSIX.1-2008 (ed. 2013) [0] states:
If source_file is a file of type symbolic link:
If the -R option was not specified, cp shall take actions based on
the type and contents of the file referenced by the symbolic link,
and not by the symbolic link itself, unless the -P option was
specified.
So far, so good. As far as I know, coreutils' cp fully respect this.
If the -R option was specified:
If none of the options -H, -L, nor -P were specified, it is
unspecified which of -H, -L, or -P will be used as a default.
Somewhere in the past, coreutils team has opted for using '-P'
(DEREF_NEVER) in this case. Anyway this leads to an inconsistence in
the behaviour of cp:
$ touch file ; ln -s file symlink ; for o in "" -r ; do cp $o
symlink cp$o ; done ; ls -liog
total 0
8224776 -rw-r--r-- 1 0 Nov 4 23:15 cp
8224777 lrwxrwxrwx 1 4 Nov 4 23:15 cp-r -> file
8224774 -rw-r--r-- 1 0 Nov 4 23:15 file
8224775 lrwxrwxrwx 1 4 Nov 4 23:15 symlink -> file
What wrong with it ? The problem is that we got a modified dereference
setting just by using '--recursive', an unrelated option. Moreover,
recursion and dereferencing are orthogonal features and there's no
reason one should imply the other.
As for my opinion, there are three possibilities for, at least, reduce
this perceived inconsistency.
1. leave `cp -R` acting as it currently does...
...but properly document it. The texinfo doc already cites this
behaviour, but both the man page and the help (imo, the two most used
sources while searching for an option) don't. I would suggest adding
"Implies '--no-dereference'" to the description of the -r/-R option.
2. let `cp -R` act as if `-L` is used.
This is my preferred option, but it's also the most invasive. All the
scripts using `cp -r` for copying a directory tree without dereferencing
the symbolic links would fail. The texinfo doc warns against that use
[1]:
-- doc/coreutils.texi:8334
[...] It is not portable to use
@option{-r} to copy symbolic links or special files. On some
non-GNU systems, @option{-r} implies the equivalent of
@option{-L} and @option{--copy-contents} for historical reasons.
Also, it is not portable to use @option{-R} to copy symbolic links
unless you also specify @option{-P}, as POSIX allows
implementations that dereference symbolic links by default.
so maybe this option could be considered. But honestly, despite being my
preferred option (i.e.: the one I would implement if I had to write a
'cp' utility from scratch), I'm not sure I can endorse it as it would be
highly backward incompatible.
3. let `cp -R` act as if `-H` is used.
This is a sort of compromise between the other two options. It gains
some consistency ( `cp` and `cp -R` would act the same with regard to
dereferencing the symlinks passed on the command line ) and would
preserve a certain level of backward compatibility. I expect the
percentage of real-case scripts that would be broken by this change to
be really minimal.
I don't particularly like this option, but if option 2. is judged
impractical (as it probably is), I personally largely prefer this
solution over option 1.
The attached preliminary patch implements option 3.
After applying the patch the following tests fail:
= tests/cp/r-vs-symlink.sh
This is expected, as it is the point of the patch. Anyway the comments
in the test file are suspicious:
# cp -r should not create symlinks. Fixed in fileutils-4.1.5.
# Restored old behavior (whereby cp -r preserves symlinks) in 4.1.6,
# though now such usage evokes a warning:
# cp: 'slink': WARNING: using -r to copy symbolic links is not
# portable
So maybe a similar change (probably option 2. above) was implemented,
and reverted, in the past ? I wasn't able to find a reference to it in
the Changelog, so cannot tell why it has been reverted. Anyway the
warning cited in the comment doesn't seem to exist anymore.
= tests/cp/special-f.sh [2]
This is unexpected. At a first look, the failure should be caused by the
following test not being fully inclusive:
-- src/copy.c:1930
else if (! S_ISDIR (dst_sb.st_mode)
/* Never unlink dst_name when in move mode. */
&& ! x->move_mode
&& (x->unlink_dest_before_opening
|| (x->preserve_links && 1 < dst_sb.st_nlink)
|| (x->dereference == DEREF_NEVER
&& ! S_ISREG (src_sb.st_mode))
))
I hadn't the time for investigate further, will do in the next days. At
the moment, however, I suspect the previous dereference settings was
simply masking and underlying issue.
Ciao,
Gian Piero.
[0] http://pubs.opengroup.org/onlinepubs/9699919799/utilities/cp.html
[1] Anyway I'm not sure why it differentiates between '-r' and '-R',
given that in coreutils' cp they are aliases:
-- src/copy.c:1045
case 'r':
case 'R':
x.recursive = true;
break;
[2] A side note about this test. The comment seems to contradict the
code:
-- tests/cp/special-f.sh:28
# Without -f, expect it to fail
cp -R fifo e || fail=1
As for my impression, it also contradicts POSIX specifications (w/o -f
it should fail). Anyway this belongs to another bug report.
[draft.patch (text/x-diff, attachment)]
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