prepare-root: Add support for root.transient #3114

cgwalters · 2023-12-07T18:31:56Z

sysroot: Drop unused prototype

This function doesn't exist anymore.

prepare-root: Add an autofree

This doesn't matter at all, but I just noticed this while working
on the code.

prepare-root: Add support for root.transient

Closes: #3113

It'd greatly improve compatibility with things like RPMs that install
in /opt if we supported a full "original docker" style model where
/ is a transient overlayfs. We'd still keep our semantics for /etc
and /var by default, but e.g. we'd stop recommending
/opt ➡️ /var/opt, in this model,
so /opt would be on the overlayfs.

Note this all aligns with composefs, where we'd actually be making
/ a read-only overlayfs by default; it'd be really nice of course
to implement this by just making the composefs overlayfs writable,
but I am not sure we can hard require composefs for this right now.

So this change adds support for root.transient = true
in /usr/lib/ostree/prepare-root.conf.

The major downside is that people could be surprised if files they
write to e.g. /opt don't persist across upgrades. But, that's
already again how it works since Docker started.

Note as part of the implementation of this, we need to add a whole
new "backing" directory distinct from the deployment directories.

(Tangentially related to this, it's tempting to switch to always
using a read-only overlay mount by default.

This function doesn't exist anymore.

This doesn't matter at all, but I just noticed this while working on the code.

Closes: ostreedev#3113 It'd greatly improve compatibility with things like RPMs that install in `/opt` if we supported a full "original docker" style model where `/` is a transient overlayfs. We'd still keep our semantics for `/etc` and `/var` by default, but e.g. we'd stop recommending `/opt` ➡️ `/var/opt`, in this model, so `/opt` would be on the overlayfs. Note this all aligns with composefs, where we'd actually be making `/` a *read-only* overlayfs by default; it'd be really nice of course to *implement* this by just making the composefs overlayfs writable, but I am not sure we can hard require composefs for this right now. So this change adds support for `root.transient = true` in `/usr/lib/ostree/prepare-root.conf`. The major downside is that people could be surprised if files they write to e.g. `/opt` don't persist across upgrades. But, that's already again how it works since Docker started. Note as part of the implementation of this, we need to add a whole new "backing" directory distinct from the deployment directories. (Tangentially related to this, it's tempting to switch to always using a *read-only* overlay mount by default.

openshift-ci · 2023-12-07T18:32:01Z

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

cgwalters · 2023-12-07T18:33:52Z

So this seems to work well:

[root@cosa-devsh ~]# findmnt /
TARGET
  SOURCE  FSTYPE  OPTIONS
/ overlay overlay rw,relatime,seclabel,lowerdir=.,upperdir=../../backing/4b42f60ddbb87dbcabdf17e15b1414234ce03eefab0b2f0c2e7972dc1bb816bf.0/root-transient/upper,workdir=../../backing/4b42f60ddbb87dbcabdf17e15b1414234ce03eefab0b2f0c2e7972dc1bb816bf.0/root-transient/work,uuid=on

Then I did rm /opt && mkdir /opt, changes there persist across reboot.

A next step here is to change rpm-ostree to detect this configuration and stop doing the opt ➡️ var/opt link (edit: done in coreos/rpm-ostree#4719 )

This pairs with ostreedev/ostree#3114 Basically we want to detect the case where the OS has opted-in to this new mode and *not* symlink things. I originally thought we could implement this by just moving all the toplevel directories, but then I hit on the fact that because the `filesystem` package is creating all the toplevel directories in lua script which we ignore...that doesn't work. So we need to keep making them by hand.

This pairs with ostreedev/ostree#3114 Basically if ostree has an overlayfs (whether writable or a readonly composefs), we're safe to handle non-`/usr` content. However, we still *always* drop content from the "API filesystems" like `/run`, `/dev` etc. Because really, no one should be adding stuff there.

cgwalters · 2023-12-08T12:59:47Z

This also wants ostreedev/ostree-rs-ext#570

This turns on the functionality added in ostreedev/ostree#3114

cgwalters · 2023-12-08T13:08:45Z

BTW this change also requires coreos/coreos-installer#1203 for FCOS for the same reason as composefs.
And will also trip over os-prober failing. os-prober is just the worst 😢
Anyways though, I think I'd like to just get this (and all its dependent patches) in since it should be inert code until explicitly turned on (example).

rhatdan · 2023-12-08T13:23:09Z

LGTM
@vrothberg @jlebon PTAL

ericcurtin

LGTM

jlebon · 2023-12-08T14:27:05Z

src/libostree/ostree-sysroot-deploy.c

@@ -3360,6 +3407,9 @@ sysroot_finalize_deployment (OstreeSysroot *self, OstreeDeployment *deployment,
  if (!selinux_relabel_var_if_needed (self, sepolicy, os_deploy_dfd, cancellable, error))
    return FALSE;

+  if (!sysroot_initialize_deployment_backing (self, deployment, sepolicy, error))


Shouldn't this be gated on root.transient?

You're right to call this out, but this was semi-intentional because one thing I want to do is change usroverlay to write here instead of the /var/tmp it does today - because that would just be better; the content would be clearly "lifecycle bound" to the deployment and we wouldn't need that hacky tmpfiles.d snippet we carry:

# https://github.com/ostreedev/ostree/issues/393 R! /var/tmp/ostree-unlock-ovl.*

(That said to do that note we'd need to also change some logic to ensure the overlay content for it is actually removed on reboot by default)

This all said, yes we could still create it dynamically in either case. I think we actually should have logic here in ostree to do what is being replicated in ostree-rs-ext and rpm-ostree around querying the initramfs config. Then we could drop the ex-integrity.composefs repo config.

jlebon · 2023-12-08T14:27:22Z

src/libostree/ostree-sysroot-deploy.c

@@ -3078,6 +3078,10 @@ sysroot_initialize_deployment (OstreeSysroot *self, const char *osname, const ch
  if (!require_stateroot (self, osname, error))
    return FALSE;

+  g_autofree char *stateroot_backing = g_strdup_printf ("ostree/deploy/%s/backing", osname);
+  if (!glnx_shutil_mkdir_p_at (self->sysroot_fd, stateroot_backing, 0700, cancellable, error))


And this too.

This pairs with ostreedev/ostree#3114 Basically we want to detect the case where the OS has opted-in to this new mode and *not* symlink things. I originally thought we could implement this by just moving all the toplevel directories, but then I hit on the fact that because the `filesystem` package is creating all the toplevel directories in lua script which we ignore...that doesn't work. So we need to keep making them by hand.

This pairs with ostreedev/ostree#3114 Basically if ostree has an overlayfs (whether writable or a readonly composefs), we're safe to handle non-`/usr` content. However, we still *always* drop content from the "API filesystems" like `/run`, `/dev` etc. Because really, no one should be adding stuff there.

This builds on top of the test image using ostreedev/ostree#3114 and related PRs.

This pairs with ostreedev/ostree#3114 Basically we want to detect the case where the OS has opted-in to this new mode and *not* symlink things. I originally thought we could implement this by just moving all the toplevel directories, but then I hit on the fact that because the `filesystem` package is creating all the toplevel directories in lua script which we ignore...that doesn't work. So we need to keep making them by hand.

cgwalters · 2023-12-20T16:39:24Z

BTW for people seeing this now, it's also worth looking at #3120

travier · 2024-01-10T18:50:58Z

It's unclear to me reading the commit message and the issues here what exactly happens when we turn this knob on. Could you write a bit of docs about it? Thanks

cgwalters added 3 commits December 7, 2023 13:31

sysroot: Drop unused prototype

6cb15c3

This function doesn't exist anymore.

prepare-root: Add an autofree

59cdd61

This doesn't matter at all, but I just noticed this while working on the code.

openshift-ci bot added the do-not-merge/work-in-progress label Dec 7, 2023

github-actions bot added the area/prepare-root Issue relates to ostree-prepare-root label Dec 7, 2023

cgwalters mentioned this pull request Dec 7, 2023

composepost: Support rootfs.transient=yes coreos/rpm-ostree#4719

Merged

cgwalters mentioned this pull request Dec 8, 2023

Support non-/usr content if ostree configured with overlayfs ostreedev/ostree-rs-ext#570

Merged

cgwalters marked this pull request as ready for review December 8, 2023 12:54

openshift-ci bot removed the do-not-merge/work-in-progress label Dec 8, 2023

cgwalters added a commit to cgwalters/centos-bootc that referenced this pull request Dec 8, 2023

ostree: Enable root.transient = true by default

e6761c2

This turns on the functionality added in ostreedev/ostree#3114

cgwalters mentioned this pull request Dec 8, 2023

ostree: Enable root.transient = true by default CentOS/centos-bootc#98

Merged

ericcurtin approved these changes Dec 8, 2023

View reviewed changes

ericcurtin merged commit 071053d into ostreedev:main Dec 8, 2023
24 checks passed

jlebon reviewed Dec 8, 2023

View reviewed changes

cgwalters mentioned this pull request Dec 8, 2023

using bootc install-to-filesystem osbuild/bootc-image-builder#18

Open

cgwalters added a commit to cgwalters/rhel9-bootc-demos that referenced this pull request Dec 11, 2023

cude: Build using transient-root image

7c4df44

This builds on top of the test image using ostreedev/ostree#3114 and related PRs.

cgwalters mentioned this pull request Dec 11, 2023

cuda: Build using transient-root image mrguitar/rhel9-bootc-demos#1

Merged

cgwalters added a commit to cgwalters/rhel9-bootc-demos that referenced this pull request Dec 11, 2023

cuda: Build using transient-root image

b11aed5

This builds on top of the test image using ostreedev/ostree#3114 and related PRs.

cgwalters mentioned this pull request Dec 19, 2023

RHEL 9: Filesystem customizations for edge-raw-image osbuild/images#255

Merged

cgwalters mentioned this pull request Dec 20, 2023

extensible metadata on deployments #3032

Open

cgwalters mentioned this pull request Jan 10, 2024

Support empty toplevel mount points coreos/rpm-ostree#337

Open

This was referenced Jan 15, 2024

edge-raw-image with custom partition mount points does not boot after upgrade osbuild/images#352

Open

New image type: Fedora iot-bootable-container osbuild/images#361

Merged

Release 2024.1 #3141

Merged

jlebon mentioned this pull request Mar 8, 2024

Ship dnf in FCOS and RHCOS coreos/fedora-coreos-tracker#1687

Open

jlebon mentioned this pull request Apr 24, 2024

Complete composefs integration in Fedora CoreOS coreos/fedora-coreos-tracker#1718

Closed

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prepare-root: Add support for root.transient #3114

prepare-root: Add support for root.transient #3114

cgwalters commented Dec 7, 2023

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travier commented Jan 10, 2024

prepare-root: Add support for root.transient #3114

prepare-root: Add support for root.transient #3114

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