From: A Tammy <openbsd.tech@aisha.cc>
Subject: Re: Question about cp -P (without -R) and POSIX compliance
To: Hiltjo Posthuma <hiltjo@codemadness.org>, tech@openbsd.org
Date: Sun, 6 Oct 2024 17:11:37 -0400


On 10/6/24 5:50 AM, Hiltjo Posthuma wrote:
> On Tue, Sep 17, 2024 at 12:28:45PM +0200, Hiltjo Posthuma wrote:
>> On Thu, Sep 05, 2024 at 09:44:45PM +0200, Hiltjo Posthuma wrote:
>>> Hi,
>>>
>>> I have a question about cp on OpenBSD and the -P flag.
>>>
>>> It seems cp -P (without the -R option) to copy a symlink behaves differently
>>> for single files on OpenBSD than POSIX specifies and compared to NetBSD,
>>> FreeBSD, Linux (GNU, busybox, toybox, etc).
>>>
>>> Test-case to reproduce it:
>>>
>>> 	touch file
>>> 	ln -s file link
>>> 	cp -P link link2
>>> 	ls -l link link2


For anyone curious about what is happening, on debian I get

$ ls -l link link2
lrwxrwxrwx 1 epsilon epsilon 4 Oct  6 20:59 link -> file
lrwxrwxrwx 1 epsilon epsilon 4 Oct  6 20:59 link2 -> file


On openbsd I get


# ls -l link link2
lrwxr-xr-x  1 root  wheel  4 Oct  6 23:03 link@ -> file
-rw-r--r--  1 root  wheel  0 Oct  6 23:03 link2


Personally, I think the documentation in the openbsd man page is correct
and sufficient.
Regarding the posix docs, the way I read it, the -P flag is only going
to modify the behaviour of the -R flag, if specified, and doesn't make
any sense to have -P by itself.

At the end of the day, we can bikeshed as much as we want but this
difference in behaviour is here to stay and is unlikely to be changed.


>>>
>>> NetBSD and FreeBSD changed the check a while ago (Feb 23, 2022), for example:
>>>
>>> 	https://github.com/freebsd/freebsd-src/commit/97e13037915c22162f199461f56951793d669f57
>>>
>>> Snippet:
>>>
>>> 	} else if (!Pflag) {
>>> 		fts_options &= ~FTS_PHYSICAL;
>>> 		fts_options |= FTS_LOGICAL | FTS_COMFOLLOW;
>>>
>>> The OpenBSD man page specifies:
>>>
>>> "if the -R option is also specified, no symbolic links are followed".
>>>
>>> and:
>>>
>>> "Symbolic links are always followed unless the -R flag is set, in which case
>>> symbolic links are not followed, by default. The -H or -L flags (in conjunction
>>> with the -R flag) cause symbolic links to be followed as described above. The
>>> -H, -L, and -P options are ignored unless the -R option is specified. In
>>> addition, these options override each other and the command's actions are
>>> determined by the last one specified."
>>>
>>>
>>> But POSIX specifies:
>>>
>>> "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."
>>>
>>> Reference: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/cp.html
>>>
>>> Should this be changed?
>>>
>>> Thank you,
>>>
>> Hi,
>>
>> Any thoughts about the above? Feedback would be appreciated.
>>
>> If the proposed change looks good I can write a full patch and documentation
>> update.
>>
>> Thank you,
>>
> One more try: any thought about the above?
>