Re: Status of hibernation (suspend to disk) in Guix

[Ivan Vilata i Balaguer <ivan@selidor.net>]

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Ivan Vilata i Balaguer (2022-12-12 21:11:53 +0100) wrote:

> Mekeor Melire (2022-12-10 01:00:24 +0000) wrote:
> 
> > > What about the "filefrag" executable from the "e2fsprogs" package.
> > > According to this article, it can be used in place of the deprecated
> > > uswsusp suite:
> > >
> > > https://www.linuxuprising.com/2021/08/how-to-enable-hibernation-on-ubuntu.html
> 
> Good find!  Besides the issue of `filefrag` being ExtFS-specific, another
> thing that worries me is [this check][1] that `swap-offset` does about the
> swap header being physically contiguous on disk, which would need to be made
> manually with `filefrag`.
> 
> [1]: https://git.kernel.org/pub/scm/linux/kernel/git/rafael/suspend-utils.git/tree/swap-offset.c#n114

I had a quick look to the [source code of mkswap][1] and it does take care of
checking whether the swap file has holes in it (look for the word "hole").  If
it has, it prints a warning (but it continues).  For instance:

```
$ dd if=/dev/zero of=swap bs=512 count=1 seek=1000
1+0 records in
1+0 records out
512 bytes copied, 0.000234313 s, 2.2 MB/s
$ mkswap swap

mkswap: swap contains holes or other unsupported extents.
        This swap file can be rejected by kernel on swap activation!
        Use --verbose for more details.

Setting up swapspace version 1, size = 496 KiB (507904 bytes)
no label, UUID=3c5920cb-04ee-4713-8008-c2c1bebc2f6f
```

[1]: https://github.com/util-linux/util-linux/blob/master/disk-utils/mkswap.c

Since it's unlikely that the file will change its block arrangement on disk,
and enlarging it requires another invocation of `mkswap`, it's probably enough
to tell the user to check for such warnings on `mkswap` invocation (in section
"(guix)Keyboard Layout, Networking, and Partitioning"), and then instructing
them to use `filefrag` in "(guix)Swap Space" should be ok.

I can work on an additional patch for that, but I can't ensure that it'll be
ready before 1.4.0 (I'm not in the dev team, so I don't know what the planning
for the release is 😉).

Cheers!

-- 
Ivan Vilata i Balaguer -- https://elvil.net/

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