From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ivanoab6.miniserver.com ([5.153.251.140]:34134 "EHLO www.kot-begemot.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726241AbeLKRlQ (ORCPT ); Tue, 11 Dec 2018 12:41:16 -0500 Subject: Re: [RFC v3 11/19] kunit: add Python libraries for handing KUnit config and kernel To: Steven Rostedt , Petr Mladek Cc: brakmo@fb.com, Knut Omang , jeffm@suse.com, Brendan Higgins , dri-devel@lists.freedesktop.org, Sasha Levin , Linux Trace Devel , linux-kselftest@vger.kernel.org, shuah@kernel.org, Rob Herring , Frank Rowand , linux-nvdimm@lists.01.org, mpe@ellerman.id.au, Eric Sandeen , Kieran Bingham , Matthew Wilcox , Felix Guo , Joel Stanley , Kent Overstreet , jdike@addtoit.com, Tim.Bird@sony.com, linux-um@lists.infradead.org, Julia Lawall , dan.j.williams@intel.com, kunit-dev@googlegroups.com, richard@nod.at, Greg KH , Linux Kernel Mailing List , Luis Chamberlain , Eryu Guan , Daniel Vetter , Kees Cook , joe@perches.com, linux-fsdevel@vger.kernel.org, khilman@baylibre.com References: <20181128193636.254378-1-brendanhiggins@google.com> <20181128193636.254378-12-brendanhiggins@google.com> <841cf4ae-501b-05ae-5863-a51010709b67@ideasonboard.com> <20181204204701.GT28501@garbanzo.do-not-panic.com> <20181206153718.GD24603@bombadil.infradead.org> <20181211140926.7wzd5jh6klcfsfgz@pathway.suse.cz> <20181211094140.2a928fe7@gandalf.local.home> From: Anton Ivanov Message-ID: <34f9e9f3-6bca-f11f-097c-c6e0cb779b61@cambridgegreys.com> Date: Tue, 11 Dec 2018 17:01:48 +0000 MIME-Version: 1.0 In-Reply-To: <20181211094140.2a928fe7@gandalf.local.home> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-trace-devel-owner@vger.kernel.org List-ID: On 12/11/18 2:41 PM, Steven Rostedt wrote: > On Tue, 11 Dec 2018 15:09:26 +0100 > Petr Mladek 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/