Re: [PATCH] PM / hibernate: Introduce snapshot test mode for hibernation

From: Pavel Machek
Date: Wed Jul 13 2016 - 06:22:10 EST


> On 2016???07???13??? 17:50, Pavel Machek wrote:
> >On Thu 2016-07-07 14:40:58, Chen Yu wrote:
> >>This mode is to verify if the snapshot data written to
> >>swap device can be successfully restored to memory. It
> >>is useful to ease the debugging process on hibernation,
> >>since this mode can not only bypass the BIOSen/bootloader,
> >>but also the system re-initialization.
> >>
> >>For example:
> >>$ sudo echo snapshot > /sys/power/disk
> >>$ sudo echo disk > /sys/power/state
> >>
> >>/* manual resume.*/
> >>$ sudo echo 8:3 > /sys/power/resume
> >Your examples will not work, will they?
> It works on my platform, although I did not tested it for too many
> rounds.

Please check again:

sudo echo disk > /sys/power/state
-bash: /sys/power/state: Permission denied

...because bash does the open, not echo.

> >This is also quite tricky/dangerous. If you do this with filesystems
> >mounted R/W, it is "good bye, filesystems".
> Ah, yes, this is quite tricky, maybe we can use this option as a
> debug method,
> for example, boot with rootfs = initrd, without mounting any disks,
> and then swapon the swap device, and do a testing. This should be safer?

Yeah, that's the way. Read-only root is other option.

> >I guess updating documentation would be welcome from my side,
> >otherwise it should be ok.
> OK, I'll update the documents.

Just add fat warning into the documentation.

(cesky, pictures)