Date: Tue, 26 Dec 2017 08:25:22 -0600 From: Mike Karels <karels@FreeBSD.org> To: freebsd-arch@freebsd.org Subject: making SW_WATCHDOG dynamic Message-ID: <201712261425.vBQEPMmQ007578@mail.karels.net>
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There is a kernel option, SW_WATCHDOG, which adds a low-level software watchdog in hardclock. By default, the kernel and watchdogd support only hardware-based watchdogs. There is also a callout-based software watchdog that can be enabled by watchdogd with an ioctl if --softwatchdog is specified, but watchdogd doesn't switch on its own. The SW_WATCHDOG option adds a lower-level software watchdog to the hardware-based mechanism, but it adds it unconditionally. I propose to include the SW_WATCHDOG facility by default, but enable it only if there is no hardware watchdog. I'm interested in any comments, suggestions, or background; feel free to mail me off the list. If there are multiple people interested, I'll forward messages to that group. I want to make the change because I have found SW_WATCHDOG quite useful at $JOB, and it's annoying to have to build a custom kernel just for this (not just once, but every time there is a kernel patch). Also, I'm curious why we have two software watchdog facilities. The --softwatchdog facility has various options on expiration, such as printf/log/panic; I don't know why anything other than panic/reboot would be desirable, though. I already contacted some of the people who have left fingerprints on watchdog. Also, if anyone wants to review the code, let me know. Thanks, Mikehome | help
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