On Mon 2019-02-25 17:41:50, John Ogness wrote: > On 2019-02-25, Petr Mladek <pmladek@xxxxxxxx> wrote: > >> >> vprintk_emit and vprintk_store are the main functions that all printk > >> >> variants eventually go through. Change these to store the message in > >> >> the new printk ring buffer that the printk kthread is reading. > >> > > >> > Please, are there any candidates or plans to reuse the new ring > >> > buffer implementation? > >> > >> As you pointed out below, this patch already uses the ring buffer > >> implementation for a totally different purpose: NMI safe dynamic memory > >> allocation. > > > > I have found an alternative solution. We could calculate the length > > of the formatted string without any buffer: > > > > va_list args_copy; > > > > va_copy(args_copy, args); > > len = vscprintf(NULL, fmt, args_copy); > > va_end(args_copy); > > > > This vsprintf() mode was implemented for exactly this purpose. > > For vprintk_emit() that would work. As you will see in later (patch 23), > the sprint_rb ringbuffer is used for dynamic memory allocation for > kmsg_dump functions as well. It looks dangerous to share a limited buffer between core kernel functionality and user-space triggered one. I mean that an unlimited number of devkmsg operations must not cause loosing printk() messages. > The current printk implementation allows readers to read directly from > the ringbuffer. The proposed ringbuffer requires the reader (printk) to > have its own buffers. > > We may be able to find an alternate solution here as well if that is > desired. I hope that we will be able to find one. The previous implementation needed some buffers as well. We should be able to use the same approach. I guess that one problem is that the new ringbuffer API is not able to copy just the text directly into the user-provided buffer. It might get solved by extending the API. Anyway, I still have to look at the remaining patches. Best Regards, Petr
