WIP: Add support for --replace-mode=alongside for ostree target

Ironically our support for `--replace-mode=alongside` breaks
when we're targeting an already extant ostree host, because when
we first blow away the `/boot` directory, this means the ostree
stack loses its knowledge that we're in a booted deployment,
and will attempt to GC it...

ostreedev/ostree-rs-ext@8fa019b
is a key part of the fix for that.

However, a notable improvement we can do here is to grow this
whole thing into a real "factory reset" mode, and this will
be a compelling answer to
coreos/fedora-coreos-tracker#399

To implement this though we need to support configuring the
stateroot and not just hardcode `default`.

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

Cargo.toml

@@ -33,3 +33,6 @@ exclude-crate-paths = [ { name = "libz-sys", exclude = "src/zlib" },
                         { name = "k8s-openapi", exclude = "src/v1_25" },
                         { name = "k8s-openapi", exclude = "src/v1_27" },
                       ]
+
+[patch.crates-io]
+ostree-ext = { path = "../../ostreedev/ostree-rs-ext/lib" }

lib/src/install.rs

@@ -459,11 +459,17 @@ async fn initialize_ostree_root_from_self(
 
     // TODO: make configurable?
     let stateroot = STATEROOT_DEFAULT;
-    Task::new_and_run(
-        "Initializing ostree layout",
-        "ostree",
-        ["admin", "init-fs", "--modern", rootfs.as_str()],
-    )?;
+    let has_ostree = rootfs_dir.try_exists("ostree/repo")?;
+    if !has_ostree {
+        Task::new_and_run(
+            "Initializing ostree layout",
+            "ostree",
+            ["admin", "init-fs", "--modern", rootfs.as_str()],
+        )?;
+    } else {
+        println!("Reusing extant ostree layout");
+        let _ = crate::utils::open_dir_remount_rw(rootfs_dir, "sysroot".into())?;
+    }
 
     // Default to avoiding grub2-mkconfig etc., but we need to use zipl on s390x.
     // TODO: Lower this logic into ostree proper.
@@ -482,10 +488,15 @@ async fn initialize_ostree_root_from_self(
             .quiet()
             .run()?;
     }
-    Task::new("Initializing sysroot", "ostree")
-        .args(["admin", "os-init", stateroot, "--sysroot", "."])
-        .cwd(rootfs_dir)?
-        .run()?;
+    let stateroot_exists = rootfs_dir.try_exists(format!("ostree/deploy/{stateroot}"))?;
+    if stateroot_exists {
+        anyhow::bail!("Cannot redeploy over extant stateroot {stateroot}");
+    } else {
+        Task::new("Initializing sysroot", "ostree")
+            .args(["admin", "os-init", stateroot, "--sysroot", "."])
+            .cwd(rootfs_dir)?
+            .run()?;
+    }
 
     // Ensure everything in the ostree repo is labeled
     state.lsm_label(&rootfs.join("ostree"), "/usr".into(), true)?;
@@ -532,6 +543,7 @@ async fn initialize_ostree_root_from_self(
     options.kargs = Some(kargs.as_slice());
     options.target_imgref = Some(&target_imgref);
     options.proxy_cfg = Some(proxy_cfg);
+    options.no_clean = has_ostree;
     println!("Creating initial deployment");
     let state =
         ostree_container::deploy::deploy(&sysroot, stateroot, &src_imageref, Some(options)).await?;
@@ -845,6 +857,18 @@ async fn install_to_filesystem_impl(state: &State, rootfs: &mut RootSetup) -> Re
     }
 
     let boot_uuid = rootfs.get_boot_uuid()?;
+    // If we're doing an alongside install, then the /dev bootupd sees needs to be the host's.
+    // What we probably really want to do here is tunnel in the host's /dev properly, but for now
+    // just copy /dev/disk
+    if rootfs.skip_finalize {
+        if !Utf8Path::new("/dev/disk").try_exists()? {
+            Task::new_and_run(
+                "Copying host /dev/disk",
+                "cp",
+                ["-a", "/proc/1/root/dev/disk", "/dev/disk"],
+            )?;
+        }
+    }
     crate::bootloader::install_via_bootupd(&rootfs.device, &rootfs.rootfs, boot_uuid)?;
     tracing::debug!("Installed bootloader");
 
@@ -958,7 +982,8 @@ fn remove_all_in_dir_no_xdev(d: &Dir) -> Result<()> {
 
 #[context("Removing boot directory content")]
 fn clean_boot_directories(rootfs: &Dir) -> Result<()> {
-    let bootdir = rootfs.open_dir(BOOT).context("Opening /boot")?;
+    let bootdir =
+        crate::utils::open_dir_remount_rw(rootfs, BOOT.into()).context("Opening /boot")?;
     // This should not remove /boot/efi note.
     remove_all_in_dir_no_xdev(&bootdir)?;
     if ARCH_USES_EFI {

lib/src/utils.rs

@@ -2,8 +2,12 @@ use std::os::unix::prelude::OsStringExt;
 use std::process::Command;
 
 use anyhow::{Context, Result};
+use camino::Utf8Path;
+use cap_std_ext::{cap_std::fs::Dir, prelude::CapStdExtCommandExt};
+use fn_error_context::context;
 use ostree::glib;
 use ostree_ext::ostree;
+use std::os::fd::AsFd;
 
 /// Try to look for keys injected by e.g. rpm-ostree requesting machine-local
 /// changes; if any are present, return `true`.
@@ -32,6 +36,44 @@ pub(crate) fn find_mount_option<'a>(
         .next()
 }
 
+/// Try to (heuristically) determine if the provided path is a mount root.
+pub(crate) fn is_mountpoint(root: &Dir, path: &Utf8Path) -> Result<Option<bool>> {
+    // https://github.com/systemd/systemd/blob/8fbf0a214e2fe474655b17a4b663122943b55db0/src/basic/mountpoint-util.c#L176
+    use rustix::fs::{AtFlags, StatxFlags};
+
+    // SAFETY(unwrap): We can infallibly convert an i32 into a u64.
+    let mountroot_flag: u64 = libc::STATX_ATTR_MOUNT_ROOT.try_into().unwrap();
+    match rustix::fs::statx(
+        root.as_fd(),
+        path.as_std_path(),
+        AtFlags::NO_AUTOMOUNT | AtFlags::SYMLINK_NOFOLLOW,
+        StatxFlags::empty(),
+    ) {
+        Ok(r) => {
+            let present = (r.stx_attributes_mask & mountroot_flag) > 0;
+            Ok(present.then(|| r.stx_attributes & mountroot_flag > 0))
+        }
+        Err(e) if e == rustix::io::Errno::NOSYS => Ok(None),
+        Err(e) => Err(e.into()),
+    }
+}
+
+/// Given a target directory, if it's a read-only mount, then remount it writable
+#[context("Opening {target} with writable mount")]
+pub(crate) fn open_dir_remount_rw(root: &Dir, target: &Utf8Path) -> Result<Dir> {
+    if is_mountpoint(root, target)?.unwrap_or_default() {
+        tracing::debug!("Target {target} is a mountpoint, remounting rw");
+        let st = Command::new("mount")
+            .args(["-o", "remount,rw", target.as_str()])
+            .cwd_dir(root.try_clone()?)
+            .status()?;
+        if !st.success() {
+            anyhow::bail!("Failed to remount: {st:?}");
+        }
+    }
+    root.open_dir(target).map_err(anyhow::Error::new)
+}
+
 /// Run a command in the host mount namespace
 #[allow(dead_code)]
 pub(crate) fn run_in_host_mountns(cmd: &str) -> Command {