On Fri, Aug 21, 2020 at 7:32 PM David Laight <David.Laight@xxxxxxxxxx> wrote: > > From: Nicolas Boichat > > Sent: 21 August 2020 11:28 > > > > On Fri, Aug 21, 2020 at 4:48 PM David Laight <David.Laight@xxxxxxxxxx> wrote: > > > > > > From: Steven Rostedt > > > > Sent: 21 August 2020 01:36 > > > > On Fri, 21 Aug 2020 08:13:00 +0800 > > > > Nicolas Boichat <drinkcat@xxxxxxxxxxxx> wrote: > > > > > > > > > On Thu, Aug 20, 2020 at 10:23 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > > > > > > > > > > On Thu, 20 Aug 2020 17:14:12 +0800 > > > > > > Nicolas Boichat <drinkcat@xxxxxxxxxxxx> wrote: > > > > > > > > > > > > > Technically, we could only initialize the trace_printk buffers > > > > > > > when the print env is switched, to avoid the build error and > > > > > > > unconditional boot-time warning, but I assume this printing > > > > > > > framework will eventually get removed when the driver moves out > > > > > > > of staging? > > > > > > > > > > > > Perhaps this should be converting into a trace event. Look at what bpf > > > > > > did for their bpf_trace_printk(). > > > > > > > > > > > > The more I think about it, the less I like this series. > > > > > > > > > > To make it clear, the primary goal of this series is to get rid of > > > > > trace_printk sprinkled in the kernel by making sure some randconfig > > > > > builds fail. Since my v2, there already has been one more added (the > > > > > one that this patch removes), so I'd like to land 2/3 ASAP to prevent > > > > > even more from being added. > > > > > > > > > > Looking at your reply on 1/3, I think we are aligned on that goal? Is > > > > > there some other approach you'd recommend? > > > > > > > > > > Now, I'm not pretending my fixes are the best possible ones, but I > > > > > would much rather have the burden of converting to trace events on the > > > > > respective driver maintainers. (btw is there a short > > > > > documentation/tutorial that I could link to in these patches, to help > > > > > developers understand what is the recommended way now?) > > > > > > > > > > > > > I like the goal, but I guess I never articulated the problem I have > > > > with the methodology. > > > > > > > > trace_printk() is meant to be a debugging tool. Something that people > > > > can and do sprinkle all over the kernel to help them find a bug in > > > > areas that are called quite often (where printk() is way too slow). > > > > > > > > The last thing I want them to deal with is adding a trace_printk() with > > > > their distro's config (or a config from someone that triggered the bug) > > > > only to have the build to fail, because they also need to add a config > > > > value. > > > > > > > > I add to the Cc a few developers I know that use trace_printk() in this > > > > fashion. I'd like to hear their view on having to add a config option > > > > to make trace_printk work before they test a config that is sent to > > > > them. > > > > > > Is it worth having three compile-time options: > > > 1) trace_printk() ignored. > > > > CONFIG_TRACE=n (now) > > > > > 2) trace_printk() enabled. > > > > CONFIG_TRACE=y (now) > > > > > 3) trace_printk() generates a compile time error. > > > > CONFIG_TRACE=y and CONFIG_TRACING_ALLOW_PRINTK=n (my patch) > > > > > > > > Normal kernel builds would ignore calls. > > > Either a config option or a module option (etc) would enable it. > > > A config option that 'rand-config' builds would turn on would > > > generate compile-time errors. > > > > Yes, a config option is exactly what my patch 2/2 does. And see > > Steven's argument. > > But you were adding #ifs to you code to enable the traces. > That is just horrid. Yeah this patch 3/3 is not the best (if I understand what you mean), 1/3 type of #ifdef is actually fairly common in the kernel (an ifdef that you can enable manually in the same file, _not_ a config option). Steven's point is that both 1/3 and 3/3 should be replaced by trace events anyway. > > What you want is CONFIG_HJHJVLKHCVKIYVKIIYVYKIYVLUCLUCL=y (default n) > that would only ever get set by a 'rand-config' build and would > never be tested in any source code. What I have now is CONFIG_TRACING_ALLOW_PRINTK=n (default y). That's the same thing? Also, I'd want to enable this option on Chromium OS (i.e. set your CONFIG_HJHJVLKHCVKIYVKIIYVYKIYVLUCLUCL=y, or my CONFIG_TRACING_ALLOW_PRINTK=n), and it's likely some distros would make that choice (because they'd also do not want to see that big trace_printk warning on their production kernels). And then you end up with Steven's point (developers inconvenience when trying to add trace_printk using a config that somebody else provided to them) ,-( > > You might also want a #define that can set temporarily > to enable traces in a specific file/module even though > CONFIG_TRACE=n. I don't understand how traces are supposed to work with CONFIG_TRACE=n? > (But rand-config builds would still fail if they enabled the > 'special' option.) > > David. > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales)
