On (09/06/17 09:55), Petr Mladek wrote: [..] > > but I'm not super eager to have printk-safe based buffering. > > that's why I never posted a patch set. this approach has its > > limitations. > > Ah, I am happy to read this. From the previous mails, > I got the feeling that you were eager to go this way.
naaah, not really :) [..] > > I prepend every line with the CPU number that has printk()-ed it. > > and that's helpful because one can grep and filter out messages > > from other CPUs. it's quite OK thing to have given that messages > > can be really mixed sometimes. > > > > so adding extra information to `struct printk_log' could be helpful. > > I think we had this discussion before and you didn't want to change > > the size of `struct printk_log' because that might break gdb/crash/etc > > user space tools. has it changed? > > Yup, there should be a serious reason to change 'struct printk_log'. > I am not sure if this is the case. But I am sure that there will > be need to change the structure sooner or later. > > Anyway, it seems that we will need to update all the tools > for the different time stamps, see > https://lkml.kernel.org/r/1504613201-23868-1-git-send-email-pra...@redhat.com > Then we will be more clever how painful it is. > > > > may be we can #ifdef CONFIG_PRINTK_ABC them. so... I think we don't have to update 'struct printk_log'. we can store that "extended data" at the beginning of every message, right after the prefix. NOTE: below is a very-very quick hack. so quick, that it has known problems. - the code does not handle !PREFIX messages (like printk("foo")). but I guess we can come up with a solution here. - and printk_vscnprintf() should have that CONFIG_PRINTK_ABC, which is missing in the code below. dmesg looks like this [ 3.338129] [ext: kworker/3:2/3] input: ETPS/2 Elantech Touchpad as /devices/platform/i8042/serio1/input/input7 [ 3.340653] [ext: systemd-udevd/0] mousedev: PS/2 mouse device common for all mice [ 5.554184] [ext: swapper/0/0] random: crng init done [ 33.410639] [ext: wpa_supplicant/6] IPv6: ADDRCONF(NETDEV_UP): wlp2s0: link is not ready [ 36.812187] [ext: kworker/u16:5/1] wlp2s0: associated [ 36.812231] [ext: kworker/1:1/1] IPv6: ADDRCONF(NETDEV_CHANGE): wlp2s0: link becomes ready if we will ever decide to add any sort of "extended data" to every message, then may be we can do it this way? --- kernel/printk/printk.c | 31 ++++++++++++++++++++++++++++++- 1 file changed, 30 insertions(+), 1 deletion(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index a64c52c19b03..d7380cb70fb5 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1936,6 +1936,35 @@ static size_t log_output(int facility, int level, enum log_flags lflags, const c return log_store(facility, level, lflags, 0, dict, dictlen, text, text_len); } +static size_t printk_vscnprintf(char *text, size_t text_sz, + const char *fmt, va_list args) +{ + size_t printed = 0; + bool do_prefix = false; + + if (fmt[0] == KERN_SOH_ASCII) { + text[0] = fmt[0]; + text[1] = fmt[1]; + + if (fmt[1] != 'c') + do_prefix = true; + + fmt += 2; + printed = 2; + } + + if (do_prefix) { + printed += snprintf(text + printed, + text_sz - printed, + "[ext: %s/%d] ", + current->comm, + smp_processor_id()); + } + + printed += vscnprintf(text + printed, text_sz - printed, fmt, args); + return printed; +} + asmlinkage int vprintk_emit(int facility, int level, const char *dict, size_t dictlen, const char *fmt, va_list args) @@ -1962,7 +1991,7 @@ asmlinkage int vprintk_emit(int facility, int level, * The printf needs to come first; we need the syslog * prefix which might be passed-in as a parameter. */ - text_len = vscnprintf(text, sizeof(textbuf), fmt, args); + text_len = printk_vscnprintf(text, sizeof(textbuf), fmt, args); /* mark and strip a trailing newline */ if (text_len && text[text_len-1] == '\n') {
