install: Add kargs to installation config

We know we eventually want "day 2" management of kargs, but
supporting "install time" kargs in a somewhat container-native
way will let us more properly set up things like the `console=`
karg only for cloud images for example.

Signed-off-by: Colin Walters <walters@verbum.org>

.github/workflows/ci.yml

@@ -113,11 +113,23 @@ jobs:
           echo 'deb http://cz.archive.ubuntu.com/ubuntu lunar main universe' | sudo tee -a /etc/apt/sources.list
           sudo apt update
           sudo apt upgrade skopeo
+      - name: Build derived image
+        run: |
+          mkdir -p usr/lib/bootc/install
+          cat > usr/lib/bootc/install/50-test-kargs.conf << 'EOF'
+          [install]
+          kargs = ["localtestkarg=somevalue", "otherlocalkarg=42"]
+          EOF
+          cat >Containerfile << 'EOF'
+          FROM quay.io/centos-boot/fedora-tier-1:eln
+          COPY usr usr
+          EOF
+          podman build -t localhost/testimage .
       - name: Integration tests
         run: |
           set -xeuo pipefail
           sudo podman run --rm -ti --privileged -v /:/target -v ./usr/bin/bootc:/usr/bin/bootc --pid=host --security-opt label=disable \
-            quay.io/centos-boot/fedora-tier-1:eln bootc install-to-filesystem --target-no-signature-verification \
+          localhost/testimage bootc install-to-filesystem --skip-fetch-check --target-no-signature-verification \
             --karg=foo=bar --disable-selinux --replace=alongside /target
-          ls -al /boot/loader/
           sudo grep foo=bar /boot/loader/entries/*.conf
+          sudo grep localtestkarg=somevalue /boot/loader/entries/*.conf

docs/install.md

@@ -96,21 +96,32 @@ in that case you will need to specify `--skip-fetch-check`.
 
 ### Operating system install configuration required
 
-The container image **MUST** define its default install configuration.  For example,
-create `/usr/lib/bootc/install/00-exampleos.toml` with the contents:
+The container image **MUST** define its default install configuration.  A key choice
+that bootc by default lives up to the operating system image is the root filesystem
+type.
+
+To enable `bootc install` as part of your OS/distribution base image,
+create a file named `/usr/lib/bootc/install/00-<osname>.toml` with the contents of the form:
 
 ```toml
 [install]
 root-fs-type = "xfs"
 ```
 
-At the current time, `root-fs-type` is the only available configuration option, and it **MUST** be set.
+The `root-fs-type` value **MUST** be set.
 
 Configuration files found in this directory will be merged, with higher alphanumeric values
 taking precedence.  If for example you are building a derived container image from the above OS,
 you could create a `50-myos.toml`  that sets `root-fs-type = "btrfs"` which will override the
 prior setting.
 
+Other available options, also under the `[install]` section:
+
+`kargs`: This allows setting kernel arguments which apply only at the time of `bootc install`.
+This option is particularly useful when creating derived/layered images; for example, a cloud
+image may want to have its default `console=` set, in contrast with a default base image.
+The values in this field are space separated.
+
 ## Installing an "unconfigured" image
 
 The bootc project aims to support generic/general-purpose operating

lib/src/install.rs

@@ -381,7 +381,10 @@ pub(crate) mod config {
     #[derive(Debug, Clone, Serialize, Deserialize, Default)]
     #[serde(rename = "install", rename_all = "kebab-case", deny_unknown_fields)]
     pub(crate) struct InstallConfiguration {
+        /// Root filesystem type
         pub(crate) root_fs_type: Option<super::baseline::Filesystem>,
+        /// Kernel arguments, applied at installation time
+        pub(crate) kargs: Option<Vec<String>>,
     }
 
     impl InstallConfiguration {
@@ -392,7 +395,12 @@ pub(crate) mod config {
                     *s = Some(o);
                 }
             }
-            mergeopt(&mut self.root_fs_type, other.root_fs_type)
+            mergeopt(&mut self.root_fs_type, other.root_fs_type);
+            if let Some(other_kargs) = other.kargs {
+                self.kargs
+                    .get_or_insert_with(|| Default::default())
+                    .extend(other_kargs)
+            }
         }
     }
 
@@ -434,10 +442,43 @@ root-fs-type = "xfs"
         let other = InstallConfigurationToplevel {
             install: Some(InstallConfiguration {
                 root_fs_type: Some(Filesystem::Ext4),
+                kargs: None,
             }),
         };
         install.merge(other.install.unwrap());
         assert_eq!(install.root_fs_type.unwrap(), Filesystem::Ext4);
+
+        let c: InstallConfigurationToplevel = toml::from_str(
+            r##"[install]
+root-fs-type = "ext4"
+kargs = ["console=ttyS0", "foo=bar"]
+"##,
+        )
+        .unwrap();
+        let mut install = c.install.unwrap();
+        assert_eq!(install.root_fs_type.unwrap(), Filesystem::Ext4);
+        let other = InstallConfigurationToplevel {
+            install: Some(InstallConfiguration {
+                root_fs_type: None,
+                kargs: Some(
+                    ["console=tty0", "nosmt"]
+                        .into_iter()
+                        .map(ToOwned::to_owned)
+                        .collect(),
+                ),
+            }),
+        };
+        install.merge(other.install.unwrap());
+        assert_eq!(install.root_fs_type.unwrap(), Filesystem::Ext4);
+        assert_eq!(
+            install.kargs,
+            Some(
+                ["console=ttyS0", "foo=bar", "console=tty0", "nosmt"]
+                    .into_iter()
+                    .map(ToOwned::to_owned)
+                    .collect()
+            )
+        )
     }
 }
 

lib/src/install/baseline.rs

@@ -350,6 +350,14 @@ pub(crate) fn install_create_rootfs(
         .into_iter()
         .flatten()
         .chain([rootarg, RW_KARG.to_string(), bootarg].into_iter())
+        .chain(
+            state
+                .install_config
+                .kargs
+                .iter()
+                .flatten()
+                .map(ToOwned::to_owned),
+        )
         .collect::<Vec<_>>();
 
     mount::mount(&rootdev, &rootfs)?;