On Thu, 2008-02-07 at 11:27 -0500, Dave Anderson wrote:
> Andrew Hecox wrote:
> > On Thu, 2008-02-07 at 10:32 -0500, Dave Anderson wrote:
> >> Andrew Hecox wrote:
> >>> hello,
> >>>
> >>> I'm looking at a customer issue where diskdumpmsg is unable to read a
> >>> vmcore file. It is not clear if this a problem with the vmcore file or
> >>> diskdumpmsg. I can load the vmcore with crash and in my naive usage of
> >>> it, can see no problems. However, I'm new to the tool so that doesn't
> >>> give me a lot of confidence.
> >>>
> >>> Does anyone have any suggestions on how or if I can use crash to help
> >>> determine if there's corruption in the vmcore file? Or any other way of
> >>> approaching the problem?
> >>>
> >>> Thanks much,
> >>>
> >>> Andrew
> >>>
> >> I'm not sure what you expect the crash utility to do -- if it comes
> >> up to a prompt with no error or warning messages, it means that the
> >> ELF header contains what appears to be valid usable information,
> >> and that the minimum kernel memory contents required to set up the
> >> crash utility's notion of the running system are all in place. That's
> >> not to say that there is no chance that the vmcore contains some
> >> corruption that was not recognized.
> >>
> >
> > Thanks. Any other suggestions on how to determine if a vmcore is "valid"
> > or is that not even a reasonable question to try and ask? The problem
> > I'm trying to solve is described better below:
> >
> >> With respect to diskdumpmsg, as I understand it, it was fairly recently
> >> changed from a perl script to a C file so that it could be run
> >> earlier in time so as to be able to use the swap partition. Looking
> >> at main() in the diskdumpmsg.c file (version 1.4.1-2), there are numerous
> >> error types and associated error messages. What do you mean when you
> >> say that "diskdumpmsg is unable to read a vmcore file"?
> >
> > Specifically:
> >
> > - user reported a floating point exception from diskdump on startup
> > - the result was reproducible locally but only with their vmcore file
> > - fpe occurred in get_logbuf:
> > log_end %= log_buf_len;
> > - log_buf_len had been set to 0 in read_buffer
> > if (!page_is_dumpable(pfn, dump->device)) {
> > memset(buf, 0, copy_len);
> > } else {
> > - I don't know enough to say if the page really wasn't dumpable.
> > static inline bool page_is_dumpable(unsigned int nr, DumpDevice *device)
> > {
> > return device->dumpable_bitmap[nr>>3] & (1 << (nr & 7));
> > }
> > - I wrote a patch with one way to avoid the FPE (attached) and sent it
> > to SEG.
> >
> > Now I'm trying to determine if the vmcore file should be readable by
> > diskdumpmsg. In other words, is this a problem in diskdumpmsg post-crash
> > or a problem with the vmcore file prior to it getting to diskdumpmsg.
> > Unfortunately, I don't understand the problem domain very well at all,
> > hence the probably naive questions :)
> >
> > Any suggestions are appreciated.
> >
> > -Andrew
>
> So it appears that the page containing the log_buf_len symbol is not
> readable or contained in the dumpfile. BTW, is this a compressed
> dumpfile or an ELF formatted dumpfile? And what "dump_level" did
> they configure?
>
compressed, level is 19.
> Anyway, back to the log_buf_len symbol read, what happens when you
> enter the "log" command while in a crash session? It attempts to
> read that symbol immediately.
>
I get what appears to be a full and valid dump of the kernel message
buffer.
-Andrew
>
> Dave
>
>
> >>
> >> ------------------------------------------------------------------------
> >>
> >> diff -rupN diskdumputils-1.4.1.orig/diskdumpmsg.c diskdumputils-1.4.1/diskdumpmsg.c
> >> --- diskdumputils-1.4.1.orig/diskdumpmsg.c 2008-02-06 14:32:41.000000000 -0500
> >> +++ diskdumputils-1.4.1/diskdumpmsg.c 2008-02-06 15:56:22.000000000 -0500
> >> @@ -208,6 +208,10 @@ static int get_logbuf(DumpFile *dump, ch
> >>
> >> len = log_end;
> >> } else {
> >> + if (!log_buf_len) {
> >> + ret = READ_ERROR_IN_DUMP_FILE;
> >> + goto err;
> >> + }
> >> log_end %= log_buf_len;
> >>
> >> ret = read_buffer(dump, log_buf + log_end,
>
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