"Guilherme G. Piccoli" <gpicc...@linux.vnet.ibm.com> writes:
> Currently the xmon debugger is set only via kernel boot command-line. > It's disabled by default, and can be enabled with "xmon=on" on the > command-line. Also, xmon may be accessed via sysrq mechanism, but once > we enter xmon via sysrq, it's kept enabled until system is rebooted, > even if we exit the debugger. A kernel crash will then lead to xmon > instance, instead of triggering a kdump procedure (if configured), for > example. > > This patch introduces a debugfs entry for xmon, allowing user to query > its current state and change it if desired. Basically, the "xmon" file > to read from/write to is under the debugfs mount point, on powerpc > directory. Reading this file will provide the current state of the > debugger, one of the following: "on", "off", "early" or "nobt". Writing > one of these states to the file will take immediate effect on the debugger. I like this in general. But I think we can simplify it a bit. I don't think we need the nobt state anymore. As far as I can see it was added as a way to reinstate the old behaviour when the auto backtrace mode was added, but I've never heard of anyone using it. If anyone hits a crash where they really need that feature they can always just hack the code to disable the backtrace. So I think step 1 is a patch to drop the xmon_no_auto_backtrace stuff. Also I'm not sure EARLY needs to be a separate state. It's just a one-off invocation at boot, all we really need is just a single bit of state communicated from early_parse_xmon() to xmon_setup(), ie. a static bool would do. If we agree with that, then there's only two states left, on and off, in which case it can probably just be an int - and we can use a simple attribute file rather than custom parsing. > * I had this patch partially done for some time, and after a discussion > at the kernel slack channel latest week, I decided to rebase and fix > some remaining bugs. I'd change 'x' option to always disable the debugger, Not quite. 'x' should exit and leave xmon in whatever state it was previously in. cheers
