Re: [PATCH] x86: adjust initial setting of watchdog kind

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.03.2024 21:35, Andrew Cooper wrote:
> On 25/01/2024 2:12 pm, Jan Beulich wrote:
>> "watchdog_timeout=0" is documented to disable the watchdog. Make sure
>> this also is true when there's a subsequent "watchdog" command line
>> option (and no further "watchdog_timeout=" one).
> 
> We also document that latest takes precedence, at which point "watchdog"
> would re-activate.

True, so perhaps ...

>> While there also switch watchdog_setup() to returning void, bringing it
>> in line with the !CONFIG_WATCHDOG case. Further amend command line
>> documentation to also mention the implicit effect of specifying a non-
>> zero timeout.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> Alternatively "watchdog" following "watchdog_timeout=0" could be taken
>> to mean to use the default timeout again.

... this alternative wants following.

> I realise that watchdog_timeout is my fault, but in fairness it was an
> early change of mine in Xen and didn't exactly get the kind of review it
> would get these days.  It also wasn't used by XenServer in the end - we
> just stayed at a default 5s.
> 
> I'm very tempted to suggest deleting watchdog_timeout, and extending
> watchdog= to have `force | <bool> | <int>s` so you could specify e.g.
> `watchdog=10s`.
> 
> The watchdog is off by default so I don't expect this will impact
> people.  It is also more convenient for the end user, and means that we
> don't have have the current split approach of two separate options
> fighting for control over each other.

While I'd be happy to fold the two options, I don't think the watchdog
being off by default is relevant here. People using just the
watchdog_timeout= option with a non-zero value will already have the
watchdog enabled. They'd need to pay attention to an eventual CHANGELOG
entry and change their command line.

Furthermore consolidating the two options isn't going to remove any
of the problems. What effect would e.g. "watchdog=off,10s" have? The
principle of "latest takes precedence" assigns clear meaning to
"watchdog=off watchdog=10s", but the above remains as ambiguous as
e.g. "watchdog=force,0s". I'd be inclined to follow those to the
letter, i.e. "watchdog=off,10s" sets the timeout to 10 but disables
the watchdog while "watchdog=force,0s" simply results in a non-
functioning watchdog (due to 0s effectively meaning 4 billion seconds
and hence for all practical purposes "never").

Jan