linux-kernel - Re: Suspend to disk: do we HAVE to use swap?

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Date:	Tue, 31 Oct 2006 23:51:49 +0100
From:	"Luca Tettamanti" <kronos.it@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	"Alistair John Strachan" <s0348365@....ed.ac.uk>,
	linux-kernel@...r.kernel.org,
	"John Richard Moser" <nigelenki@...cast.net>
Subject: Re: Suspend to disk: do we HAVE to use swap?

On 10/31/06, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Tuesday, 31 October 2006 21:15, Luca Tettamanti wrote:
> > Il Tue, Oct 31, 2006 at 08:19:37PM +0100, Rafael J. Wysocki ha scritto:
> > > 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@....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).
> >
> > Of course it's also possibile to use FIBMAP ioctl:
> >
> > #include <stdio.h>
> > #include <fcntl.h>
> > #include <unistd.h>
> > #include <sys/ioctl.h>
> > #include <linux/fs.h>
> >
> > int main(int argc, char **argv) {
> >         int block = 0;
> >         int fd;
> >
> >         if (argc < 2)
> >                 return 1;
> >
> >         fd = open(argv[1], O_RDONLY);
> >         if (fd < 0) {
> >                 perror("open()");
> >                 return 1;
> >         }
> >
> >         if (ioctl(fd, FIBMAP, &block)) {
> >                 perror("ioctl()");
> >                 return 1;
> >         }
> >
> >         close(fd);
> >         printf("%d\n", block);
> >
> >         return 0;
> > }
> >
> > Probably it's more script friendly (grepping dmesg? hmmm) ;)
>
> That's a bit more complicated, because you need to find a block which is
> PAGE_SIZE big and express the number in PAGE_SIZE units.

Ah, I see. Finding a cluster of contiguous blocks is easy, but I'm
having troubles converting the block number to an offset from the
start of the device :s

Luca
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