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

[Anton Ivanov]

On 12/11/18 2:41 PM, Steven Rostedt wrote:
> On Tue, 11 Dec 2018 15:09:26 +0100
> Petr Mladek <pmladek@xxxxxxxx> 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

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