watchdogd stat location

[Warner Losh]

On Fri, Sep 27, 2019, 1:21 PM mike tancsa <mike at sentex.net> wrote:

> On 9/27/2019 3:19 PM, Oleksandr Rybalko wrote:
> >
> > пт, 27 вер. 2019 о 19:22 Warner Losh <imp at bsdimp.com
> > <mailto:imp at bsdimp.com>> пише:
> >
> >     On Fri, Sep 27, 2019 at 9:36 AM mike tancsa <mike at sentex.net
> >     <mailto:mike at sentex.net>> wrote:
> >
> >     > We sometimes run into an issue where our embedded devices that
> >     boot off
> >     > a read only SD card, hang with a controller error.  Its not clear
> if
> >     > this is a BIOS/firmware/SDCard or driver bug issue. Its pretty
> >     > infrequent, but annoying enough that I started to dig to see why
> >     the box
> >     > is not rebooting via the hardware watchdog.   It seems to fail
> >     to reboot
> >     > the box as the stat that it does on the filesystem is off the md
> >     backed
> >     > /etc which is not impacted.  I know I could run an external
> >     program, but
> >     > would it be safer to change the default directory where the stat
> >     is done
> >     > to something that is generally not mounted via ramdisk ?
> >
> >
> > Why not just stat "/".
> >
> > I think embedded devices may have monolithic kernel w/o any loadable
> > modules and book config.
> >
> I am all for that too. Just something other than /etc or /var which are
> often mounted on ramdisk.
>

I think that / is too special to cause disk IO to ever happen. Other dirs
will sometimes not be in the cache.... The notion here, perhaps bogus, is
that we want to check the root FS is sane. The stat(2) is a cheap way to do
this that will eventually fail if / goes wonky enough. It's weak.

Warner

    ---Mike
>
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