linux-kernel - Re: [RFC v3 11/19] kunit: add Python libraries for handing KUnit config and kernel

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Message-ID: <34f9e9f3-6bca-f11f-097c-c6e0cb779b61@cambridgegreys.com>
Date:   Tue, 11 Dec 2018 17:01:48 +0000
From:   Anton Ivanov <anton.ivanov@...bridgegreys.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>
Cc:     brakmo@...com, Knut Omang <knut.omang@...cle.com>, jeffm@...e.com,
        Brendan Higgins <brendanhiggins@...gle.com>,
        dri-devel@...ts.freedesktop.org,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        Linux Trace Devel <linux-trace-devel@...r.kernel.org>,
        linux-kselftest@...r.kernel.org, shuah@...nel.org,
        Rob Herring <robh@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        linux-nvdimm@...ts.01.org, mpe@...erman.id.au,
        Eric Sandeen <sandeen@...deen.net>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Matthew Wilcox <willy@...radead.org>,
        Felix Guo <felixguoxiuping@...il.com>,
        Joel Stanley <joel@....id.au>,
        Kent Overstreet <kent.overstreet@...il.com>, jdike@...toit.com,
        Tim.Bird@...y.com, linux-um@...ts.infradead.org,
        Julia Lawall <julia.lawall@...6.fr>, dan.j.williams@...el.com,
        kunit-dev@...glegroups.com, richard@....at,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Eryu Guan <guaneryu@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Kees Cook <keescook@...gle.com>, joe@...ches.com,
        linux-fsdevel@...r.kernel.org, khilman@...libre.com
Subject: Re: [RFC v3 11/19] kunit: add Python libraries for handing KUnit
 config and kernel


On 12/11/18 2:41 PM, Steven Rostedt wrote:
> On Tue, 11 Dec 2018 15:09:26 +0100
> Petr Mladek <pmladek@...e.com> wrote:
>
>>> We have liburcu already, which is good.  The main sticking points are:
>>>
>>>   - printk has started adding a lot of %pX enhancements which printf
>>>     obviously doesn't know about.
>> I wonder how big problem it is and if it is worth using another
>> approach.
> No, please do not change the %pX approach.
>
>> An alternative would be to replace them with helper functions
>> the would produce the same string. The meaning would be easier
>> to understand. But concatenating with the surrounding text
>> would be less elegant. People might start using pr_cont()
>> that is problematic (mixed lines).
>>
>> Also the %pX formats are mostly used to print context of some
>> structures. Even the helper functions would need some maintenance
>> to keep them compatible.
>>
>> BTW: The printk() feature has been introduced 10 years ago by
>> the commit 4d8a743cdd2690c0bc8 ("vsprintf: add infrastructure
>> support for extended '%p' specifiers").
> trace-cmd and perf know about most of the %pX data and how to read it.
> Perhaps we can extend the libtraceevent library to export a generic way
> to read data from printk() output for other tools to use.

Going back for a second to using UML for this. UML console at present is 
interrupt driven - it emulates serial IO using several different 
back-ends (file descriptors, xterm or actual tty/ptys). Epoll events on 
the host side are used to trigger the UML interrupts - both read and write.

This works OK for normal use, but may result in all kinds of interesting 
false positives/false negatives when UML is used to run unit tests 
against a change which changes interrupt behavior.

IMO it may be useful to consider some alternatives specifically for unit 
test coverage purposes where printk and/or the whole console output 
altogether bypass some of the IRQ driven semantics.

-- 

Anton R. Ivanov

Cambridge Greys Limited, England and Wales company No 10273661
http://www.cambridgegreys.com/