Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: Suspend to disk: do we HAVE to use swap? | Date | Tue, 31 Oct 2006 22:20:46 +0100 |
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On Tuesday, 31 October 2006 21:15, John Richard Moser wrote: > > Luca Tettamanti wrote: > > Il Tue, Oct 31, 2006 at 02:41:11PM -0500, John Richard Moser ha scritto: > >> Rafael J. Wysocki wrote: > >>> On Tuesday, 31 October 2006 20:05, Alistair John Strachan wrote: > >>>> On Tuesday 31 October 2006 17:40, Luca Tettamanti wrote: > >>>>> Alistair John Strachan <s0348365@sms.ed.ac.uk> ha scritto: > >>>>>> On Tuesday 31 October 2006 06:16, Rafael J. Wysocki wrote: > >>>>>> [snip] > >>>>>> > >>>>>>> However, we already have code that allows us to use swap files for the > >>>>>>> suspend and turning a regular file into a swap file is as easy as > >>>>>>> running 'mkswap' and 'swapon' on it. > >>>>>> How is this feature enabled? I don't see it in 2.6.19-rc4. > >>>>> Swap files have been supported for ages. suspend-to-swapfile is very > >>>>> new, you need a -mm kernel and userspace suspend from CVS: > >>>>> http://suspend.sf.net > >>>> I know, I use swap files, and not a partition. This has prevented me from > >>>> using suspend to disk "for ages". ;-) > >>>> > >>>> Is userspace suspend REQUIRED for this feature? > >>> No, but unfortunately one piece is still missing: You'll need to figure out > >>> where your swap file's header is located. > >>> > >>> However, if you apply the attached patch the kernel will tell you where it is > >>> (after you do 'swapon' grep dmesg for 'swap' and use the value in the > >>> 'offset' field). > >> Nobody has answered this one yet: Once you 'swapon' doesn't the kernel > >> have (require?) the swap file opened writable? Simple mode: > >> > >> IS THIS NOT EXTREMELY DANGEROUS? > > > > The trick is that the FS hosting the swapfile is *not* mounted at all; > > you don't even activate the swap. resume process uses the block number > > (better: the couple <devid, block>) to locate the swapfile. > > The "ugly" part of this method is that the user has to figure out the > > first block of the swapfile, since at resume time it's not possibile to > > mount the fs (not even read only - journaled filesystems will blow up > > due to journal replay) to search the swap area... > > > > Yes, I was referring to Wysoki's comment about using swapon to find it. > Although I guess you could look beforehand; but then if you move the > partition around on disk the block changes (and the kernel, on resume, > goes "BOY WHAT IS WRONG WITH YOU?!" because the partition table is > incorrect XD)
Well, if you change your partition table between the suspend and resume, the resume will fail anyway (in the very best case).
Greetings, Rafael
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