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[Xen-devel] [PATCH 0/6] printk log level and print rate.

The following is a rewrite of the printk log levels (plus the added print rate limit) as for Keir's suggestions.

This touches a lot so please test.

We have now four log levels to choose from, as well as a GUEST flag for prints that are controlled by something that a guest does. I tried to go though practically all DPRINTKs to see what level it should be and whether or not a GUEST should be tagged to it. But, being human and not knowing the fine details of the code surrounding the prints, I'm sure I tagged things wrong. So that said, here are the new tags:

XENLOG_ERR - non guest fatal error message. The ship is sinking.
XENLOG_WARNING - non guest warning message, we can plug the holes.
XENLOG_INFO - non guest info message, counting the fish we catch.
XENLOG_DEBUG - non guest debug message, keep all fish, even if they are
              under the limit.

XENLOG_G_ERR - guest fatal error, One of the boats is sinking.
XENLOG_G_WARNING - guest warning message, we can dump the water out.
XENLOG_G_INFO - guest info message, count the people on board.
XENLOG_G_DEBUG - guest debug message, smuggle the illegal immigrants.

Basically, we don't trust guests. So we differentiate the guest messages with the _G_ option so that we can process these prints differently. Basically, we add a print rate limit to them.

On a domain crash, I also added a oops_in_progress to notify that all prints should be printed regardless.

There's also a xen_startup variable, that currently isn't set, but it should be set to 1 on startup (print everything) and cleared after dom0 is up and running. I haven't added this in yet.

There's 4 thresholds too.

For both the non-guest and guest, they have an upper and lower threshold. Since ERR is 0 and DEBUG is 3, what these thresholds represent is that anything above the upper is ignored, anything below the lower is always printed, and any thing in between (inclusive) is rate limited.

If the lower is greater than the upper, then only the upper is recognized, and there is no rate limiting performed. All above the upper is ignored, and all below or equal to the upper is printed.


1) Have xen_startup = 1 on startup and turned to zero later.
2) Add a config option for changing the default thresholds
3) Having a keyhandler to change the default thresholds
4) Add a hypercall to let Dom0 change the default thresholds
5) Add a sysctl to have userspace in Dom0 change the default thresholds
    (** seeing a pattern here? **)
6) Tag the bare printks to use the log levels.

Currently (as Keir suggested) the default thresholds are:

non guest: upper=1 lower=2 (ERR/WARNING printed, but nothing else)
guest: upper=1 lower=0 (ERR/WARNING print rated, nothing else printed)

Feel free to comment.

-- Steve

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