On Mon, Dec 3, 2018 at 2:55 AM Petr Mladek <pmladek@xxxxxxxx> wrote: > > On Thu 2018-11-29 19:29:24, Luis Chamberlain wrote: > > On Wed, Nov 28, 2018 at 11:36:20AM -0800, Brendan Higgins wrote: > > > A number of test features need to do pretty complicated string printing > > > where it may not be possible to rely on a single preallocated string > > > with parameters. > > > > > > So provide a library for constructing the string as you go similar to > > > C++'s std::string. > > > > Hrm, what's the potential for such thing actually being eventually > > generically useful for printk folks, I wonder? Petr? > > printk() is a bit tricky: > > + It should work in any context. Any additional lock adds risk of a > deadlock. Especially the NMI and scheduler contexts are problematic. > There are problems with any other code that might be called > from console drivers and calls printk() under a lock. > > + It should work also when the system is out of memory. Especially > atomic context is problematic because we could not wait for > memory reclaim or swap. > > + We also do to the best effort to get the message out on the > console. It is important when the system is about to die. > Any extra buffering layer might cause delay and avoid seeing the > message. > > From this point of views, this API is not generally usable with printk(). Yeah, that makes sense. I wouldn't really expect this to work well in those cases. > Now, the question is how many of the above fits also for unit testing. > At least, you might need to be careful when allocating memory in > atomic context. True, but this is only supposed to be used for constructing expectation failure messages which should only happen from a non-atomic context. > > BTW: There are more existing printk APIs: Well, I admit the they are > not easily reusable in unit testing: > > + printk() is old, crappy code, complicated with all the > cornercases and consoles. > > + include/linux/seq_buf.h is simple buffering. It is used primary > for sysfs output. It might be usable if you add support for > loglevel and use big enough buffer. I quess that you should > flush the buffer regularly anyway. > > + trace_printk() uses lockless per-CPU buffers. It currently does not > support loglevels. But it might be pretty interesting choice as well. > > > I do not say that you have to use one of the existing API. But you > might consider them if you encouter any problems and maintaining > your variant gets complicated. Alright, I will take a look. Thanks! _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
