On 05/16/2012 08:08 AM, Wolfgang Denk wrote: > Dear Tim, > > In message <4fb2c002.5030...@am.sony.com> you wrote: >> Support same log buffer or tracing buffer in both bootloader and kernel >> >> ; Summary: Support same log buffer or tracing buffer in both bootloader and >> kernel >> ; Proposer: Tim Bird - Sony Network Entertainment >> >> == Description == >> It would be nice to share log buffer or trace buffers between the bootloader >> and the kernel, >> so that either log messages or trace events (respectively) could be >> coalesced from both sources in a >> unified view. > > This has been a standard feature in U-Boot for many years. > > The corresponding Linux code is also available; see for example > https://lkml.org/lkml/2009/1/21/250 > and commit 212f61c in git://git.denx.de/linux-denx.git > > The code has recently been resubmitted by Heiko Schocher, and as far > as I can tell it is supposed to hit mainline any time soon. > >> It appears that U-boot uses a log-buffer format similar to the Linux kernel. > > Not only similar, but identical (which is intentional). > >> Note that this is useful for on-box analysis (using 'dmesg' locally, and >> getting both >> bootloader and kernel messages). It is obvious that someone with a serial >> console > > It actually works round-trip: i. e. you can see in U-Boot the last > log messages of the previously running kernel, which may be helpful if > messages were written to the log buffer, but the kernel crashed before > these could be processed otherwise. And as long as you don't clear > the log buffer, you can still read these messages in Linux after > rebooting (assuming sane hardware which does not lose memory content > during a warmboot - U-Boot takes care to preserve this information > during a reboot). > >> Handling trace events in a coalesced fashion is a whole other issue. > ... >> * Does u-boot support any tracing code similar to ftrace? > > No, U-Boot does not support any such feature (yet). > >> == Scope == >> Unknown > > Scope should be small. As mentioned, the patches are queued. > >> == Contractor Candidates == >> No one so far. > > I would recommend Heiko Schocher here, who has been working on this in > several iterations before, and who submitted the most recent set of > patches.
Thanks. This is very helpful. Are you aware of the churn going on right now with regards to the kernel printk code? Kay Sievers has proposed a structured logging system, which will alter the format of the messages as they are stored in the log buffer. I don't know if it will be backwards compatible with the stuff you have in U-boot or not. This has not been mainlined yet, but it's probably worth following what is going on there. See http://thread.gmane.org/gmane.linux.kernel/1277619 ============================= Tim Bird Architecture Group Chair, CE Workgroup of the Linux Foundation Senior Staff Engineer, Sony Network Entertainment ============================= _______________________________________________ Celinux-dev mailing list Celinux-dev@lists.celinuxforum.org https://lists.celinuxforum.org/mailman/listinfo/celinux-dev
