cvs commit: src/sys/ddb db_command.c db_output.c

Nate Lawson nate at
Mon Oct 3 09:45:54 PDT 2005

Robert Watson wrote:
> On Sun, 2 Oct 2005, Olivier Houchard wrote:
>> cognet      2005-10-02 22:57:31 UTC
>>  FreeBSD src repository
>>  Modified files:
>>    sys/ddb              db_command.c db_output.c
>>  Log:
>>  - Call db_setup_paging() for traceall.
>>  - Make it so one can't call db_setup_paging() if it has already been 
>> called
>>  before. traceall needs this, or else the db_setup_paging() call from
>>  db_trace_thread() will reset the printed line number, and override its
>>  argument.
>>  This is not perfect for traceall, because even if one presses 'q' 
>> while in
>>  the middle of printing a backtrace it will finish printing the backtrace
>>  before exiting, as db_trace_thread() won't be notified it should 
>> stop, but
>>  it is hard to do better without reworking the pager interface a lot 
>> more.
> Thanks!
> Is there any chance I can interest you in an idea phk, I, and a few 
> others have been kicking around for a bit relating to smart small dumps? 
> Specifically, we were discussing the idea of allowing a dumping mode in 
> which rather than dumping all of kernel memory, we dump specifically the 
> common and useful output from ddb, such as ps, show locked vnods, show 
> alllocks, traceall, show allpcpu, and so on, basically in text format, 
> to the dump partition.  Then the results can be pulled off easily in a 
> format that is appropriate for e-mailing or submitting via a PR, even 
> without a full debugging kernel, etc.  Among other things, these dumps 
> would be much, much smaller than a memory dump, meaning they could be 
> kept around like log files (/var/log/crash.log.0, ...), be e-mailed to 
> the sysadmin, etc.  It would require some new magic in DDB and the 
> dumping code, but almost all of the logic to generate the information 
> from DDB could be reused, perhaps via an alternative pager or debug 
> output device :-).

That's fine as a hack-around, but I hope that doesn't distract effort 
from sparse kernel dumps.  If you throw out non-anonymous pages, buffer 
cache, etc., you end up with a very small image to begin with.  Add in 
gzip compression and it wouldn't be much larger than your uncompressed 
logs.  Then you can run whatever info tools you want against the core 
since no actual data is lost.


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