linux-kernel - Re: [PATCH 1/2] perf tools: Ensure --symfs ends with '/'

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Date:	Mon, 11 Aug 2014 10:15:48 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Minchan Kim <minchan@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>, David Ahern <dsahern@...il.com>
Subject: Re: [PATCH 1/2] perf tools: Ensure --symfs ends with '/'

Em Mon, Aug 11, 2014 at 04:38:17PM +0900, Namhyung Kim escreveu:
> On Fri, 1 Aug 2014 17:15:38 -0300, Arnaldo Carvalho de Melo wrote:
> > Em Fri, Aug 01, 2014 at 08:38:02AM +0900, Namhyung Kim escreveu:
> >> On Thu, 31 Jul 2014 09:26:21 -0300, Arnaldo Carvalho de Melo wrote:
> >> > Em Thu, Jul 31, 2014 at 01:25:52PM +0900, Namhyung Kim escreveu:
> >> >> Are you still against my approach - adding '/' at the end of the symfs
> >> >> string itself?  It seems that mine is simpler and shorter.

> >> > Yes, I am.

> >> > We are not just concatenating two strings, we are joining two path
> >> > components.

> >> > I think it is more clear and elegant to do it as python os.path.join()
> >> > does.

> >> Then I think you also need to care about trailing and leading '/' in the
> >> components so that, say, joining '/home/' and '/namhyung/' can result in
> >> '/home/namhyung/' not '/home///namhyung/'.

> > Well, "/home/namhyung/" is the same as "/home///namhyung/" for POSIX:
> > http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap03.html#tag_03_266

> > So, when we can easily avoid it, no use to have a sequence of slashes,
> > but otherwise it is harmless.
 
> Yes, I know it's supported.  But I think it'd be better off avoiding it
> in order to be an elegant path joiner. :)

Yeah, when we can do such things with just one or two lines of code,
that is ok, but if not, hey, the kernel will do it for us. I.e. there
_is_ code already to make it sane, to understand the intent. And it is
_always_ in place, since this is a standard.
 
> >> Btw, it seems like python's os.path.join() just use latter if it's an
> >> absolute path.
> >> 
> >>   $ python
> >>   Python 2.7.3 (default, Jul 24 2012, 10:05:38) 
> >>   [GCC 4.7.0 20120507 (Red Hat 4.7.0-5)] on linux2
> >>   Type "help", "copyright", "credits" or "license" for more information.
> >>   >>> import os.path
> >>   >>> os.path.join('/home/', '/namhyung/')
> >>   '/namhyung/'

> > Interesting, wonder what is the rationale for that or if this is a bug.
 
> Hmm.. pydoc os.path.join says below:
 
>  os.path.join = join(a, *p)
> 
>     Join two or more pathname components, inserting '/' as needed.  If
>     any component is an absolute path, all previous path components will
>     be discarded.  An empty last part will result in a path that ends
>     with a separator.

It states the behaviour, but doesn't present the rationale, that left me
wondering :)

- Arnaldo
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