[linux-pm] Software suspend support in Fedora.

[Pavel Machek]

Hi!

>  > > The outcome: I'm no more enthusiastic about enabling this in Red Hat
>  > > kernels than I ever was before.  It seems to have real issues with LVM
>  > > setups (which is default on Red Hat/Fedora installs these days).
>  > > After convincing it where to suspend/resume from by feeding it
>  > > the major/minor of my swap partition, it did actually seem
>  > > to suspend. And resume (though it did spew lots of 'sleeping whilst
>  > > atomic warnings, but thats trivial compared to whats coming up
>  > > next).
>  > 
>  > I do not know much about LVM. How exactly did you resume= command line
>  > look like? You were not resuming from initrd, right?
> 
> Indeed, this was very likely the problem. Doing a resume if I had
> any partition mounted was *bad* news.  We implemented the necessary
> bits in our initrd today to detect resume partitions, and erm.. resume them.
> So far so good, no repeats of the corruption I saw.

Aha, good.

> As of tomorrow rawhide kernels (for the unenlightened: these will
> eventually be FC5) will have software suspend support.
> 
> Our initial experiments with it have been fairly positive, though as
> expected there are a number of drivers that don't survive the resume
> correctly. http://www.livejournal.com/users/kernelslacker/22975.html

I see, having ext3 (or anything else) mounted when doing resume is
going to kill you data, fast. I thought warning in docs was good
enough :-).

Anyway, if you want to make this idiot-proof, I think the preferred
way is to kill suspend signature during the boot [it is must-have for
failsafe boot, so you can recover system if resume crashes it]. That
way user can echo whatever to resume, but having no signature means he
is not going to cause big damage.

[Actually there are more easy ways to kill some data. Suspend, do
normal boot next time, change something on disk, reboot and make it
resume. Bye-bye data.]

Okay, I realized I had too many warnings in there, and some things
(like no driver support) is not _that_ dangerous, while resuming with
filesystems mounted clearly is. I'll probably change the warning to:

 * BIG FAT WARNING *********************************************************
 *
 * If you touch anything on disk between suspend and resume...
 *                              ...kiss your data goodbye.
 *
 * If you do resume from initrd after your filesystems are mounted...
 *                              ...bye bye root partition.
 *                      [this is actually same case as above]
 *
 * If you have unsupported (*) devices using DMA, you may have some
 * problems. If your disk driver does not support suspend... (IDE does),
 * it may cause some problems, too. If you change kernel command line
 * between suspend and resume, it may do something wrong. If you change
 * your hardware while system is suspended... well, it was not good idea;
 * but it wil probably only crash.
 *
 * (*) suspend/resume support is needed to make it safe.



								Pavel
-- 
if you have sharp zaurus hardware you don't need... you know my address