makedumpfile --dump-dmesg option broken on 3.5 kernels and later
Dave Anderson
anderson at redhat.com
Wed Jan 30 12:11:50 EST 2013
----- Original Message -----
> Bouchard Louis <louis.bouchard at canonical.com> wrote:
>
> I now have what looks like a working patch for this issue. Thank to Dave
> Anderson (crash) and Eric Biederman (vmcore-dmesg) for having chewed
> most of the work for me.
>
> My only remaining problem is to be able to print the syslog level as is
> provided in the previous version. Currently, the kernel doesn't export
> the 'level:3' offset of the log structure in the vmcoreinfo information
> provided in the vmcore.
>
> Vivek who authored the original kernel/printk.c patch might be able to
> suggest a better way to expose log.level:3 (I did try to patch the
> kernel but got thrown away because of the nature of .level:3 that didn't
> fit the VMCOREINFO_OFFSET macro)
>
> In the meantime, I only found this kinda ugly hack to work around the
> absence of the structure element :
>
> > /*
> > * Ugly hack around absence of log.level:3
> > * Hard code log.level offset = log.dict_len + 3
> > */
> > level = (UCHAR(logptr + OFFSET(log.dict_len)+3)&level_mask);
> >
> > sprintf(buf,"<%d>[%5lld.%06ld] ",level,nanos,rem/1000);
>
> Aside from that, I get an identical dmesg output on kernel 3.5 and after.
>
> I would appreciate comments on the following before I send the patch to
> the list.
IMHO, just drop it.
As I mentioned on the crash-utility list, it's a PITA keeping up with
the log structure changes, especially when it involves bit-fields.
The vmcore-dmesg facility just ignores displaying the message evel.
And for the next crash release, I'm putting the finishing touches on
a new "crash --log vmcore" option (i.e., without requiring the vmlinux
file), and I'm also going to ignore the log-level.
I understand that "makedumpfile --dump-dmesg" and vmcore-dmesg show
the log level for the legacy log buffer dumps, but that's because
they're embedded in the messages themselves.
Dave
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