linux-kernel - RE: [PATCH 3/3] selftests/ftrace: Use /bin/echo instead of built-in echo

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Date:   Mon, 11 May 2020 10:34:55 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Masami Hiramatsu' <mhiramat@...nel.org>,
        Xiao Yang <yangx.jy@...fujitsu.com>
CC:     Steven Rostedt <rostedt@...dmis.org>,
        Shuah Khan <shuah@...nel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Li Philip <philip.li@...el.com>,
        Liu Yiding <yidingx.liu@...el.com>
Subject: RE: [PATCH 3/3] selftests/ftrace: Use /bin/echo instead of built-in
 echo

From: Masami Hiramatsu
> Sent: 11 May 2020 10:28
...
> > We may not avoid fixing related failures after your change:
> > 1) We have to reuse built-in echo (do alias echo=echo) if we want to
> > test common_pid for histogram.
> > 2) We have to reuse built-in echo if some new tests want to interpret
> > backslash escapes in future.
> 
> 1) yes, that's what I need to do for avoiding "pid" key histogram
>   (but I think we should have better way to test it)
> 2) No, in that case you should use "/bin/echo -e" explicitly.
>    dash's built-in echo doesn't support it.
> 
> > Is it simple to provide two implementations of echo?(built-in echo and
> > echo command?) and then just apply echo command for kprobe_syntax_errors.tc?
> 
> Hmm, OK, there might be another reason we reconsider this patch.
> 
> - Alisasing echo (this patch) can avoid dash related issues but
>   this also makes "echo" running in another process implicitly.
> 
> - Using /bin/echo for backslash explicitly will be missed unless
>   user runs it on dash, but it will keep "echo" in same process.

Why not change to use printf - probably a builtin in both shells?

	David

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