install: Automatically set up bind mounts if not provided

hack/lldb/deploy.sh

@@ -11,7 +11,7 @@ sudo podman build --build-arg "sshpubkey=$(cat ~/.ssh/id_rsa.pub)" -f Containerf
 mkdir -p ~/.cache/bootc-dev/disks
 rm -f ~/.cache/bootc-dev/disks/lldb.raw
 truncate -s 10G ~/.cache/bootc-dev/disks/lldb.raw
-sudo podman run --pid=host --network=host --privileged --security-opt label=type:unconfined_t -v /dev:/dev -v /var/lib/containers:/var/lib/containers -v ~/.cache/bootc-dev/disks:/output -v /dev:/dev localhost/bootc-lldb bootc install to-disk --via-loopback --generic-image --skip-fetch-check /output/lldb.raw
+sudo podman run --pid=host --network=host --privileged --security-opt label=type:unconfined_t -v ~/.cache/bootc-dev/disks:/output localhost/bootc-lldb bootc install to-disk --via-loopback --generic-image --skip-fetch-check /output/lldb.raw
 
 # create a new VM in libvirt
 set +e

lib/src/install.rs

@@ -56,6 +56,8 @@ use crate::utils::sigpolicy_from_opts;
 const BOOT: &str = "boot";
 /// Directory for transient runtime state
 const RUN_BOOTC: &str = "/run/bootc";
+/// The default path for the host rootfs
+const ALONGSIDE_ROOT_MOUNT: &str = "/target";
 /// This is an ext4 special directory we need to ignore.
 const LOST_AND_FOUND: &str = "lost+found";
 /// The filename of the composefs EROFS superblock; TODO move this into ostree
@@ -316,9 +318,10 @@ pub(crate) struct InstallToExistingRootOpts {
     #[clap(long)]
     pub(crate) acknowledge_destructive: bool,
 
-    /// Path to the mounted root; it's expected to invoke podman with
-    /// `-v /:/target`, then supplying this argument is unnecessary.
-    #[clap(default_value = "/target")]
+    /// Path to the mounted root; this is now not necessary to provide.
+    /// Historically it was necessary to ensure the host rootfs was mounted at here
+    /// via e.g. `-v /:/target`.
+    #[clap(default_value = ALONGSIDE_ROOT_MOUNT)]
     pub(crate) root_path: Utf8PathBuf,
 }
 
@@ -333,8 +336,6 @@ pub(crate) struct SourceInfo {
     pub(crate) selinux: bool,
     /// Whether the source is available in the host mount namespace
     pub(crate) in_host_mountns: bool,
-    /// Whether we were invoked with -v /var/lib/containers:/var/lib/containers
-    pub(crate) have_host_container_storage: bool,
 }
 
 // Shared read-only global state
@@ -516,38 +517,13 @@ impl SourceInfo {
         tracing::debug!("Finding digest for image ID {}", container_info.imageid);
         let digest = crate::podman::imageid_to_digest(&container_info.imageid)?;
 
-        let have_host_container_storage = Utf8Path::new(crate::podman::CONTAINER_STORAGE)
-            .try_exists()?
-            && ostree_ext::mountutil::is_mountpoint(
-                &root,
-                crate::podman::CONTAINER_STORAGE.trim_start_matches('/'),
-            )?
-            .unwrap_or_default();
-
-        // Verify up front we can do the fetch
-        if have_host_container_storage {
-            tracing::debug!("Host container storage found");
-        } else {
-            tracing::debug!(
-                "No {} mount available, checking skopeo",
-                crate::podman::CONTAINER_STORAGE
-            );
-            require_skopeo_with_containers_storage()?;
-        }
-
-        Self::new(
-            imageref,
-            Some(digest),
-            root,
-            true,
-            have_host_container_storage,
-        )
+        Self::new(imageref, Some(digest), root, true)
     }
 
     #[context("Creating source info from a given imageref")]
     pub(crate) fn from_imageref(imageref: &str, root: &Dir) -> Result<Self> {
         let imageref = ostree_container::ImageReference::try_from(imageref)?;
-        Self::new(imageref, None, root, false, false)
+        Self::new(imageref, None, root, false)
     }
 
     fn have_selinux_from_repo(root: &Dir) -> Result<bool> {
@@ -573,7 +549,6 @@ impl SourceInfo {
         digest: Option<String>,
         root: &Dir,
         in_host_mountns: bool,
-        have_host_container_storage: bool,
     ) -> Result<Self> {
         let selinux = if Path::new("/ostree/repo").try_exists()? {
             Self::have_selinux_from_repo(root)?
@@ -585,7 +560,6 @@ impl SourceInfo {
             digest,
             selinux,
             in_host_mountns,
-            have_host_container_storage,
         })
     }
 }
@@ -716,19 +690,7 @@ async fn install_container(
             }
         };
 
-        // We need to fetch the container image from the root mount namespace.  If
-        // we don't have /var/lib/containers mounted in this image, fork off skopeo
-        // in the host mountnfs.
-        let skopeo_cmd = if !state.source.have_host_container_storage {
-            Some(run_in_host_mountns("skopeo"))
-        } else {
-            None
-        };
-        let proxy_cfg = ostree_container::store::ImageProxyConfig {
-            skopeo_cmd,
-            ..Default::default()
-        };
-
+        let proxy_cfg = ostree_container::store::ImageProxyConfig::default();
         (src_imageref, Some(proxy_cfg))
     };
     let src_imageref = ostree_container::OstreeImageReference {
@@ -895,32 +857,6 @@ pub(crate) fn exec_in_host_mountns(args: &[std::ffi::OsString]) -> Result<()> {
     Err(Command::new(cmd).args(args).exec()).context("exec")?
 }
 
-#[context("Querying skopeo version")]
-fn require_skopeo_with_containers_storage() -> Result<()> {
-    let out = Task::new_cmd("skopeo --version", run_in_host_mountns("skopeo"))
-        .args(["--version"])
-        .quiet()
-        .read()
-        .context("Failed to run skopeo (it currently must be installed in the host root)")?;
-    let mut v = out
-        .strip_prefix("skopeo version ")
-        .map(|v| v.split('.'))
-        .ok_or_else(|| anyhow::anyhow!("Unexpected output from skopeo version"))?;
-    let major = v
-        .next()
-        .ok_or_else(|| anyhow::anyhow!("Missing major version"))?;
-    let minor = v
-        .next()
-        .ok_or_else(|| anyhow::anyhow!("Missing minor version"))?;
-    let (major, minor) = (major.parse::<u64>()?, minor.parse::<u64>()?);
-    let supported = major > 1 || minor > 10;
-    if supported {
-        Ok(())
-    } else {
-        anyhow::bail!("skopeo >= 1.11 is required on host")
-    }
-}
-
 pub(crate) struct RootSetup {
     luks_device: Option<String>,
     device_info: crate::blockdev::PartitionTable,
@@ -1269,6 +1205,8 @@ async fn prepare_install(
     tracing::debug!("Target image reference: {target_imgref}");
 
     // A bit of basic global state setup
+    crate::mount::ensure_mirrored_host_mount("/dev")?;
+    crate::mount::ensure_mirrored_host_mount("/var/lib/containers")?;
     ensure_var()?;
     setup_tmp_mounts()?;
     // Allocate a temporary directory we can use in various places to avoid
@@ -1454,12 +1392,6 @@ async fn install_to_filesystem_impl(state: &State, rootfs: &mut RootSetup) -> Re
         .ok_or_else(|| anyhow!("No uuid for boot/root"))?;
     tracing::debug!("boot uuid={boot_uuid}");
 
-    // If we're doing an alongside install, then the /dev bootupd sees needs to be the host's.
-    ensure!(
-        crate::mount::is_same_as_host(Utf8Path::new("/dev"))?,
-        "Missing /dev mount to host /dev"
-    );
-
     let bound_images = BoundImages::from_state(state).await?;
 
     // Initialize the ostree sysroot (repo, stateroot, etc.)
@@ -1514,9 +1446,6 @@ pub(crate) async fn install_to_disk(mut opts: InstallToDiskOpts) -> Result<()> {
                 block_opts.device
             );
         }
-        if !crate::mount::is_same_as_host(Utf8Path::new("/dev"))? {
-            anyhow::bail!("Loopback mounts (--via-loopback) require host devices (-v /dev:/dev)");
-        }
     } else if !target_blockdev_meta.file_type().is_block_device() {
         anyhow::bail!("Not a block device: {}", block_opts.device);
     }
@@ -1705,6 +1634,23 @@ pub(crate) async fn install_to_filesystem(
     // And the last bit of state here is the fsopts, which we also destructure now.
     let mut fsopts = opts.filesystem_opts;
 
+    // If we're doing an alongside install, automatically set up the host rootfs
+    // mount if it wasn't done already.
+    if targeting_host_root
+        && fsopts.root_path.as_str() == ALONGSIDE_ROOT_MOUNT
+        && !fsopts.root_path.try_exists()?
+    {
+        tracing::debug!("Mounting host / to {ALONGSIDE_ROOT_MOUNT}");
+        std::fs::create_dir(ALONGSIDE_ROOT_MOUNT)?;
+        crate::mount::bind_mount_from_pidns(
+            crate::mount::PID1,
+            "/".into(),
+            ALONGSIDE_ROOT_MOUNT.into(),
+            true,
+        )
+        .context("Mounting host / to {ALONGSIDE_ROOT_MOUNT}")?;
+    }
+
     // Check that the target is a directory
     {
         let root_path = &fsopts.root_path;

lib/src/mount.rs

@@ -1,15 +1,36 @@
 //! Helpers for interacting with mountpoints
 
-use std::process::Command;
+use std::{
+    fs,
+    os::fd::{AsFd, OwnedFd},
+    process::Command,
+};
 
-use anyhow::{anyhow, Result};
+use anyhow::{anyhow, Context, Result};
 use bootc_utils::CommandRunExt;
 use camino::Utf8Path;
 use fn_error_context::context;
+use rustix::{
+    mount::{MoveMountFlags, OpenTreeFlags},
+    net::{
+        AddressFamily, RecvFlags, SendAncillaryBuffer, SendAncillaryMessage, SendFlags,
+        SocketFlags, SocketType,
+    },
+    process::WaitOptions,
+    thread::Pid,
+};
 use serde::Deserialize;
 
 use crate::task::Task;
 
+/// Well known identifier for pid 1
+pub(crate) const PID1: Pid = const {
+    match Pid::from_raw(1) {
+        Some(v) => v,
+        None => panic!("Expected to parse pid1"),
+    }
+};
+
 #[derive(Deserialize, Debug)]
 #[serde(rename_all = "kebab-case")]
 #[allow(dead_code)]
@@ -124,3 +145,134 @@ pub(crate) fn is_same_as_host(path: &Utf8Path) -> Result<bool> {
     );
     Ok(devstat.f_fsid == hostdevstat.f_fsid)
 }
+
+/// Given a pid, enter its mount namespace and acquire a file descriptor
+/// for a mount from that namespace.
+#[allow(unsafe_code)]
+#[context("Opening mount tree from pid")]
+pub(crate) fn open_tree_from_pidns(
+    pid: rustix::process::Pid,
+    path: &Utf8Path,
+    recursive: bool,
+) -> Result<OwnedFd> {
+    // Allocate a socket pair to use for sending file descriptors.
+    let (sock_parent, sock_child) = rustix::net::socketpair(
+        AddressFamily::UNIX,
+        SocketType::STREAM,
+        SocketFlags::CLOEXEC,
+        None,
+    )
+    .context("socketpair")?;
+    const DUMMY_DATA: &[u8] = &[b'!'];
+    match unsafe { libc::fork() } {
+        0 => {
+            // We're in the child. At this point we know we don't have multiple threads, so we
+            // can safely `setns`.
+
+            // Open up the namespace of the target process as a file descriptor, and enter it.
+            let pidlink = fs::File::open(format!("/proc/{}/ns/mnt", pid.as_raw_nonzero()))?;
+            rustix::thread::move_into_link_name_space(
+                pidlink.as_fd(),
+                Some(rustix::thread::LinkNameSpaceType::Mount),
+            )
+            .context("setns")?;
+
+            // Open the target mount path as a file descriptor.
+            let recursive = if recursive {
+                OpenTreeFlags::AT_RECURSIVE
+            } else {
+                OpenTreeFlags::empty()
+            };
+            let fd = rustix::mount::open_tree(
+                rustix::fs::CWD,
+                path.as_std_path(),
+                OpenTreeFlags::OPEN_TREE_CLOEXEC | OpenTreeFlags::OPEN_TREE_CLONE | recursive,
+            )
+            .context("open_tree")?;
+
+            // And send that file descriptor via fd passing over the socketpair.
+            let fd = fd.as_fd();
+            let fds = [fd];
+            let mut buffer = [0u8; rustix::cmsg_space!(ScmRights(1))];
+            let mut control = SendAncillaryBuffer::new(&mut buffer);
+            let pushed = control.push(SendAncillaryMessage::ScmRights(&fds));
+            assert!(pushed);
+            let ios = std::io::IoSlice::new(DUMMY_DATA);
+            rustix::net::sendmsg(sock_child, &[ios], &mut control, SendFlags::empty())?;
+            // Then we're done.
+            std::process::exit(0)
+        }
+        -1 => {
+            // fork failed
+            let e = std::io::Error::last_os_error();
+            anyhow::bail!("failed to fork: {e}");
+        }
+        n => {
+            // We're in the parent; create a pid (checking that n > 0).
+            let pid = rustix::process::Pid::from_raw(n).unwrap();
+            // Receive the mount file descriptor from the child
+            let mut cmsg_space = vec![0; rustix::cmsg_space!(ScmRights(1))];
+            let mut cmsg_buffer = rustix::net::RecvAncillaryBuffer::new(&mut cmsg_space);
+            let mut buf = [0u8; DUMMY_DATA.len()];
+            let iov = std::io::IoSliceMut::new(buf.as_mut());
+            let mut iov = [iov];
+            let nread = rustix::net::recvmsg(
+                sock_parent,
+                &mut iov,
+                &mut cmsg_buffer,
+                RecvFlags::CMSG_CLOEXEC,
+            )
+            .context("recvmsg")?
+            .bytes;
+            assert_eq!(nread, DUMMY_DATA.len());
+            assert_eq!(buf, DUMMY_DATA);
+            // And extract the file descriptor
+            let r = cmsg_buffer
+                .drain()
+                .filter_map(|m| match m {
+                    rustix::net::RecvAncillaryMessage::ScmRights(f) => Some(f),
+                    _ => None,
+                })
+                .flatten()
+                .next()
+                .ok_or_else(|| anyhow::anyhow!("Did not receive a file descriptor"))?;
+            rustix::process::waitpid(Some(pid), WaitOptions::empty())?;
+            Ok(r)
+        }
+    }
+}
+
+/// Create a bind mount from the mount namespace of the target pid
+/// into our mount namespace.
+pub(crate) fn bind_mount_from_pidns(
+    pid: Pid,
+    src: &Utf8Path,
+    target: &Utf8Path,
+    recursive: bool,
+) -> Result<()> {
+    let src = open_tree_from_pidns(pid, src, recursive)?;
+    rustix::mount::move_mount(
+        src.as_fd(),
+        "",
+        rustix::fs::CWD,
+        target.as_std_path(),
+        MoveMountFlags::MOVE_MOUNT_F_EMPTY_PATH,
+    )
+    .context("Moving mount")?;
+    Ok(())
+}
+
+// If the target path is not already mirrored from the host (e.g. via -v /dev:/dev)
+// then recursively mount it.
+pub(crate) fn ensure_mirrored_host_mount(path: impl AsRef<Utf8Path>) -> Result<()> {
+    let path = path.as_ref();
+    // If we didn't have this in our filesystem already (e.g. for /var/lib/containers)
+    // then create it now.
+    std::fs::create_dir_all(path)?;
+    if is_same_as_host(path)? {
+        tracing::debug!("Already mounted from host: {path}");
+        return Ok(());
+    }
+    tracing::debug!("Propagating host mount: {path}");
+    bind_mount_from_pidns(PID1, path, path, true)
+}

ostree-ext/.github/workflows/bootc.yml

@@ -59,7 +59,7 @@ jobs:
       - name: Integration tests
         run: |
           set -xeuo pipefail
-          sudo podman run --rm -ti --privileged -v /:/target -v /var/lib/containers:/var/lib/containers -v ./usr/bin/bootc:/usr/bin/bootc --pid=host --security-opt label=disable \
+          sudo podman run --rm -ti --privileged -v ./usr/bin/bootc:/usr/bin/bootc --pid=host --security-opt label=disable \
             quay.io/centos-bootc/centos-bootc-dev:stream9 bootc install to-filesystem \
             --karg=foo=bar --disable-selinux --replace=alongside /target