On 12/11/18 2:41 PM, Steven Rostedt wrote:
On Tue, 11 Dec 2018 15:09:26 +0100
Petr Mladek <pmladek(a)suse.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
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