Re: ISO image: to xz or not to xz?

[Vagrant Cascadian <vagrant@debian.org>]

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On 2021-05-03, Tobias Geerinckx-Rice wrote:
> Tangent: I sense some undeserved mysticism surrounding squashfs. 
> It is not designed to be loop-mounted, any more than ext2 was.  It 
> does not enjoy it.  People should stop doing it.

The only mysticism I see here is attributing enjoyment to a
filesystem. :)

Is mounting on a loopback device really any different from any other
block device?


> But they won't, because many distributions still insist that the 
> same installer image must be both a bootable CD/DVD *and* boot 
> when dd'd to a USB drive, on every PC ever made.

> That ‘isohybrid’ dream justifies doing unmentionable things to an 
> iso9660 file system (and only an iso9660 file system), so they 
> must put the real squashfs on top of that and loop-mount it and 
> ignore the screams I guess and--

Never heard the screams; what frequency does squashfs emit screams at?
:)

People have made it work well enough for only slightly less long than I
can remember using free software operating systems...


> Vagrant Cascadian 写道：
>> Well, the suggestion to use squashfs does bear merit;
>
> It's not a *bad* suggestion, just a bit obvious.

Fair enough.


>> it would require having some type of writeable filesystem on top,
>> such as using overlay fs to mount the installer rootfs with squashfs
>> for the readonly bits, and tmpfs for the writeable bits.
>
> We've always done this.

I *thought* so, but...


>> As a bonus, using a tmpfs overlay would solve the issue brought up
>> recently by someone who tried using the same installer image multiple
>> times, and /gnu/store and /var/guix got out of sync due to the
>> cow-store only writing to the newly installed system, so that the
>> second install failed.
>
> ...so no, it definitely wouldn't, but I think it's valuable to 
> understand why you thought so!
>
> Could you elaborate?

Mostly I was referring to:

  https://lists.gnu.org/archive/html/guix-devel/2021-04/msg00546.html

Though I haven't confirmed that behavior myself. Probably deserves a
proper bug report.


live well,
  vagrant

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