Re: [patch] suspend: update documentation

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > | Update suspend documentation.
> > | 
> > | Signed-off-by: Pavel Machek <pavel@suse.cz>
> > | 
> > | ---
> > | 
> > | diff --git a/Documentation/power/swsusp.txt b/Documentation/power/swsusp.txt
> > | --- a/Documentation/power/swsusp.txt
> > | +++ b/Documentation/power/swsusp.txt
> > | @@ -318,3 +318,10 @@ As a rule of thumb use encrypted swap to
> > |  system is shut down or suspended. Additionally use the encrypted
> > |  suspend image to prevent sensitive data from being stolen after
> > |  resume.
> > | +
> > | +Q: Why we cannot suspend to a swap file?
> > 
> > Q: Why can't we suspend to a swap file?
> > or
> > Q: Why can we not suspend to a swap file?
> > 
> > | +
> > | +A: Because accessing swap file needs the filesystem mounted, and
> > | +filesystem might do something wrong (like replaying the journal)
> > | +during mount. [Probably could be solved by modifying every filesystem
> > | +to support some kind of "really read-only!" option. Patches welcome.]
> 
> This is wrong. Suspend2 has supported writing to a swap file for a long
> time (since 1.0), without requiring the filesystem to be mounted when
> resuming. We just need to store the bdev and block numbers in the image
> header.

Uh, and then you pass something like resume=/dev/hda5@BLOCKID on
command line? Okay, that could work.

Does this look fair?

Q: Why can't we suspend to a swap file?

A: Because accessing swap file needs the filesystem mounted, and
filesystem might do something wrong (like replaying the journal)
during mount.

There are few ways to get that fixed:

1) Probably could be solved by modifying every filesystem to support
some kind of "really read-only!" option. Patches welcome.

2) suspend2 gets around that by storing absolute positions in on-disk
image, with resume parameter pointing directly to suspend header.


								Pavel
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