Quoting Oren Laadan (orenl@xxxxxxxxxxx):
> > BTW it occurs to me that self-restart with a logfd must be kinda
> > hosed early on :)
>
> Why would that be a problem ? I actually think it's useful for
> those doing self-restart: you open a file, the kernel takes a
> reference to it, then sys_restart() will eventually close that
> file descriptor - but kernel still keeps a reference - so debug
> data keeps flowing. When restart completes -- data is gone; If
> restart fails - user will have information in that file.
Hmm, good point. No problem then.
...
> >>> Changelog:
> >>> Oct 21: split ckpt_debug into ckpt_debug and ckpt_err.
> >>> Git rid of the split by memory debug info etc.
> >> The split is useful to control the amount of log.
> >
> > It's a stupid split! And I've never used it. Besides, when a log is
> > for a single c/r, it's really not very big.
>
> It may be stupid split!, yet it did prove very useful to me.
Sorry, stupid isn't right. Clearly it made sense.
> Maybe it's because you never debugged the memory checkpoint
> page by page.
>
> A typical scenario: you hit a bug -> you enable debugging ->
> the bug disappears -> you disable debugging -> you hit the bug ...
>
> IOW, debugging output in big doses affects the execution in a
> way that makes heisen-bugs hide. Control over verbosity means you
> get better chances at reproducing the behavior and still have
> enough meaningful data.
So I guess it should stay in there at least for syslog output.
Then you could debug by not passing an fd for the logfile to
sys_restart, and tweaking the syslog output.
> > More practically, requiring userspace to pass over a flag
> > consisting of CKPT_DBG_MEM|CKPT_DBG|FILE|CKPT_DBG|TASK, and
> > handle corresponding usage flags, is not nice.
>
> I agree with you on about this. Maybe we want a better
> interface ?
>
> Which brings me to this random thought: maybe we want to
> make the fourth argument of sys_{checkpoint,restart} a
> structure, to make it easier to extend it in the future
> without having to go throw a clone3-like hell...
>
> Specifically, this structure could now be:
>
> struct ckpt_args {
> int version;
> int logfd;
> int logmask;
> };
>
> (or use union checkpoint {} and union restart {} to tell
> between checkpoint- and restart-related args.
Well I don't like passing structs to the kernel actually (and
don't like that in the clone3 patchset :), but can't think of
anything better offhand. I'll think about it a bit more, but
maybe this'll be the way to go - long as a very simple program
can pass NULL to mean no debug.
-serge
_______________________________________________
Containers mailing list
Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linux-foundation.org/mailman/listinfo/containers
