nixos/qemu-vm: Option to use squashfs Nix store closure instead of virtfs access to host's store by chkno · Pull Request #72354 · NixOS/nixpkgs

chkno · 2019-10-31T07:09:27Z

Motivation for this change

Allow VMs built with nixos-rebuild build-vm to work without any virtfs mounts into the host. In particular, allow them to use a nix store closure in a squashfs like the installer uses.

This allows better isolation of guests. A host that runs multiple VMs may not wish the guests to be able to see each others' derivations.

Things done

chkno · 2019-11-01T17:51:48Z

(Rebased on top of #72342 so the NixOS tests can run)

chkno · 2019-11-01T18:04:42Z

@GrahamcOfBorg test qemu-private-store

matthewbauer · 2019-11-03T17:01:48Z

@GrahamcOfBorg test qemu-private-store

matthewbauer

This all looks like a good idea, though I don't have enough familiarity to really judge whether this breaks anything. Requested a few more people to review.

chkno · 2020-01-29T19:01:55Z

Updated to rebase on top of #55645. I confirm that login, upnp, installer, virtualbox, and the new test pass on x86_64-linux.

matthewbauer

Looks good!

chkno · 2020-03-19T06:27:39Z

Updated test from perl test framework to python test framework.

nixos-discourse · 2020-05-08T04:31:18Z

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-ready-for-review-may-2019/3032/157

flokli · 2020-05-24T11:06:14Z

nixos/modules/virtualisation/qemu-vm.nix

What's the difference of these?

I don't know.

By default they point at the same directory in the host. The test framework points them at different directories by setting SHARED_DIR.

History:

Aug 2011 d75efe4 edolstra: Introduced /tmp/xchg: "For security, don't mount the entire host filesystem."

Aug 2012 a025e7e edolstra: Introduced /tmp/shared: "Provide a common share between VMs to allow easy communication"

May 2020 d85dc4f erikarvstedt: Mentions "xchg is advertised as a bidirectional exchange dir."

Current uses I could find:

Mount Purpose Location

xchg coverage-data nixos/modules/testing/test-instrumentation.nix nixos/lib/test-driver/test-driver.pl

xchg runInMachine nixos/lib/testing.nix

shared copy_from_host copy_from_vm nixos/lib/test-driver/test-driver.py

I just want a lever to turn them off. I guess it makes more sense to be one lever rather than two.

I combined these two options into one and added a note about what these directories are currently used for in the option description.

@erikarvstedt @edolstra can you provide some insight here?

We can probably get rid of coverage-data. AFAIK we're not doing coverage runs in VMs anymore (and IIRC it was only used in some toy examples like the Quake 3 test anyway).

We can probably also eliminate copy_from_* since it's only used in 3 places, which can be replaced by machine.execute("cat ...").

We can probably get rid of coverage-data. AFAIK we're not doing coverage runs in VMs anymore (and IIRC it was only used in some toy examples like the Quake 3 test anyway).

I updated the list in #72828, and filed #97231 removing the remaining coverage-data references - PTAL.

flokli · 2020-07-06T18:50:41Z

This also needs a rebase.

When the store is not shared, the closure used in the VM it is packaged up in a squashfs, just like the ISO installer does.

chkno · 2020-07-06T20:39:44Z

Rebased on top of #92205, #92122, and #90280.

nh2 · 2020-07-06T21:23:10Z

nixos/modules/virtualisation/qemu-vm.nix

+            Share /tmp/shared and /tmp/xchg with the host.  These are used
+            for runInMachine, copy_from_{host,vm}, and coverage-data.


May want to use <literal> markup for easier reading, e.g.

Suggested change

Share /tmp/shared and /tmp/xchg with the host. These are used

for runInMachine, copy_from_{host,vm}, and coverage-data.

Share <literal>/tmp/shared</literal> and <literal>/tmp/xchg</literal> with the host.

These are used for <literal>runInMachine</literal>, <literal>copy_from_{host,vm}</literal>,

and <literal>coverage-data</literal>.

(Please check the manual builds after this, one can accidentlaly screw it up like I did recently.)

@nh2: ... or go even further and use <filename/> and <function/>:

Suggested change

Share /tmp/shared and /tmp/xchg with the host. These are used

for runInMachine, copy_from_{host,vm}, and coverage-data.

Share <filename class="directory">/tmp/shared</filename> and

<filename class="directory">/tmp/xchg</filename> with the host.

These are used for <function>runInMachine</function>,

<literal>copy_from_{host,vm}</literal>, and

<literal>coverage-data</literal>.

nh2 · 2020-07-06T21:33:45Z

nixos/modules/virtualisation/qemu-vm.nix

+            this makes building the VM much faster requires less disk
+            space.  Disable to give the guest a separate, fresh store
+            in a squashfs that contains only the closure of the guest's
+            dependencies.


I think the wording that contains only the closure of the guest's dependencies is a bit misleading, because it may be understood as that if you shareNixStore = true, then all of the hosts nix store is shared with the guest:

Even if you share the nix store with the host, only the closure of the guest's dependencies are "available" in the nix store; all the store paths are present as files in /nix/store, but most of those are not valid (registered in the sqlite DB).

This recently tricked me: https://discourse.nixos.org/t/how-to-build-a-nixos-vm-with-nix-in-which-nixos-rebuild-is-a-no-op/7937

Because of this ambiguity, I think we should add an explicit:

Suggested change

dependencies.

dependencies.

Note that even with <literal>virtualisation.shareNixStore = true;</literal>,

not the entire host Nix store is available in the guest Nix store:

While all <literal>/nix/store</literal> files will be present, only the ones

pulled in by <option>virtualisation.pathsInNixDB</option>

will be registered as valid in the Nix store database.

nh2 · 2020-07-06T21:34:05Z

nixos/modules/virtualisation/qemu-vm.nix

-            appear in the guest Nix store as well, but are considered
-            garbage (because they are not registered in the Nix
-            database in the guest).
+            database in the VM.  If virtualisation.shareNixStore is true,


Suggested change

database in the VM. If virtualisation.shareNixStore is true,

database in the VM. If <option>virtualisation.shareNixStore</option> is true,

nh2 · 2020-07-06T21:35:49Z

nixos/tests/qemu-private-store.nix

+    shared.succeed("[[ $(mount | grep -c virt) -gt 0 ]]")
+    private.succeed("[[ $(mount | grep -c virt) -eq 0 ]]")
+  '';
+})


New tests are great!

Optionally, maybe also add a copy of this test that exercises the default virtualisation.shareNixStore = false;?

This isn't used anymore as per NixOS#72354 (comment).

stale · 2021-03-31T06:16:46Z

I marked this as stale due to inactivity. → More info

now it works

chkno · 2021-10-25T20:53:48Z

Since ec6c604 from #127933 , this can be accomplished via configuration; it doesn't need to be explicitly supported in the qemu-vm module. Thanks, @rnhmjoj!

The necessary configuration is now available at https://github.com/chkno/nixos-qemu-vm-isolation/blob/main/modules/qemu-vm-isolation.nix , which can be used as an example or directly as a library for folks that want this feature.

rnhmjoj · 2021-10-25T21:17:58Z

Nice! It's good to know my cleanup has been useful.

chkno force-pushed the qemu-vm-isolation branch 2 times, most recently from 12cf6fe to 588aaba Compare November 1, 2019 17:50

matthewbauer requested review from aanderse, infinisil and samueldr November 3, 2019 17:01

matthewbauer reviewed Nov 3, 2019

View reviewed changes

matthewbauer requested review from bjornfor and cleverca22 November 3, 2019 17:02

chkno force-pushed the qemu-vm-isolation branch from 588aaba to 9a8668b Compare January 29, 2020 18:58

ofborg bot added 10.rebuild-linux: 1-10 This PR causes between 1 and 10 packages to rebuild on Linux. and removed 10.rebuild-linux: 0 This PR does not cause any packages to rebuild on Linux. labels Jan 29, 2020

matthewbauer approved these changes Jan 29, 2020

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chkno force-pushed the qemu-vm-isolation branch from 9a8668b to 6fc1303 Compare March 19, 2020 06:25

flokli reviewed May 24, 2020

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chkno force-pushed the qemu-vm-isolation branch from 6fc1303 to 838cfa9 Compare July 3, 2020 18:15

ofborg bot added the 10.rebuild-linux: 1 This PR causes 1 package to rebuild on Linux. label Jul 3, 2020

This was referenced Jul 3, 2020

qemu-vm device name cleanup #92205

Merged

qemu-vm: Fix useBootLoader, remove /boot read-only restriction #92122

Merged

chkno force-pushed the qemu-vm-isolation branch from 838cfa9 to 0c3bff3 Compare July 4, 2020 03:14

flokli requested a review from erikarvstedt July 6, 2020 18:49

flokli requested a review from nh2 July 6, 2020 18:50

chkno added 3 commits July 6, 2020 13:36

nixos/qemu-vm: Option to not share Nix store with host

f3df5ab

When the store is not shared, the closure used in the VM it is packaged up in a squashfs, just like the ISO installer does.

nixos/qemu-vm: New options for turning virtfs mounts off

345f1f8

nixos/qemu-vm: Test for shareNixStore = false

483393d

chkno changed the base branch from staging to master July 6, 2020 20:37

chkno force-pushed the qemu-vm-isolation branch from 0c3bff3 to 483393d Compare July 6, 2020 20:37

nh2 reviewed Jul 6, 2020

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nh2 reviewed Jul 9, 2020

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tfc mentioned this pull request Sep 5, 2020

nixos/tests: Leftover tasks towards unified Python integration tests #72828

Closed

flokli added a commit to flokli/nixpkgs that referenced this pull request Sep 5, 2020

nixos/testing: remove remaining coverage-data logic

98d6b55

This isn't used anymore as per NixOS#72354 (comment).

flokli mentioned this pull request Sep 5, 2020

nixos/testing: remove remaining coverage-data logic #97231

Merged

10 tasks

stale bot added the 2.status: stale https://github.com/NixOS/nixpkgs/blob/master/.github/STALE-BOT.md label Mar 31, 2021

r2r-dev added a commit to r2r-dev/nixos-shell that referenced this pull request May 12, 2021

Add NixOS/nixpkgs#72354 to the mix

fb3f52f

now it works

chkno closed this Oct 25, 2021

Mount	Purpose	Location
xchg	coverage-data	nixos/modules/testing/test-instrumentation.nix nixos/lib/test-driver/test-driver.pl
xchg	runInMachine	nixos/lib/testing.nix
shared	copy_from_host copy_from_vm	nixos/lib/test-driver/test-driver.py

		Share /tmp/shared and /tmp/xchg with the host. These are used
		for runInMachine, copy_from_{host,vm}, and coverage-data.

-            Share /tmp/shared and /tmp/xchg with the host.  These are used
-            for runInMachine, copy_from_{host,vm}, and coverage-data.
+            Share <literal>/tmp/shared</literal> and <literal>/tmp/xchg</literal> with the host.
+            These are used for <literal>runInMachine</literal>, <literal>copy_from_{host,vm}</literal>,
+            and <literal>coverage-data</literal>.

-            Share /tmp/shared and /tmp/xchg with the host.  These are used
-            for runInMachine, copy_from_{host,vm}, and coverage-data.
+            Share <filename class="directory">/tmp/shared</filename> and
+            <filename class="directory">/tmp/xchg</filename> with the host.
+            These are used for <function>runInMachine</function>,
+            <literal>copy_from_{host,vm}</literal>, and
+            <literal>coverage-data</literal>.

-            dependencies.
+            dependencies.
+            Note that even with <literal>virtualisation.shareNixStore = true;</literal>,
+            not the entire host Nix store is available in the guest Nix store:
+            While all <literal>/nix/store</literal> files will be present, only the ones
+            pulled in by <option>virtualisation.pathsInNixDB</option>
+            will be registered as valid in the Nix store database.

	database in the VM. If virtualisation.shareNixStore is true,
	database in the VM. If <option>virtualisation.shareNixStore</option> is true,

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Conversation

chkno commented Oct 31, 2019

Motivation for this change

Things done

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chkno commented Nov 1, 2019

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chkno commented Nov 1, 2019

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flokli commented Jul 6, 2020

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stale bot commented Mar 31, 2021

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chkno commented Oct 25, 2021

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rnhmjoj commented Oct 25, 2021

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chkno commented Jan 29, 2020 •

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