Add --mount flag for 9p host directory sharing

Add support for sharing host directories into the VM via QEMU 9p (virtio-9p). The --mount flag can be repeated; each host directory appears at the same absolute path inside the VM. Design: - QEMU: each --mount gets a short 9p tag (slim0, slim1, …) via -virtfs local,path=…,mount_tag=slimN,security_model=mapped-xattr. Tags are kept short because 9p mount_tag has a ~31-byte limit. - Kernel cmdline: the full destination path is passed as slim.mount=<tag>:<base64(path)> so the init script knows where to mount each tag. Base64 avoids issues with spaces/special chars. - slim-init.sh: after networking, parse slim.mount= entries, mkdir -p the destination, and mount -t 9p <tag> <dest> -o trans=virtio,version=9p2000.L Tests verify: 9p share detection via sysfs mount_tag, 9p entry in mount output, file content accessible at the expected path, and clean VM exit.
2026-09-10 12:19:59 +02:00
parent 6111bbeb8d
commit 90de50dfed
3 changed files with 165 additions and 4 deletions
@@ -136,6 +136,103 @@ EOF
    rm -rf "$work"
 }

+test_mount() {
+    echo "=== Testing --mount (9p shares) ==="
+
+    work="$(mktemp -d)"
+
+    # --- Image 1: no WORKINGDIR, test host:guest and multi-mount ---
+    img="slim-test-mount"
+    share_dir="$work/share"
+    share_dir2="$work/share2"
+    guest_dir="/mnt/guest"
+    guest_dir2="/mnt/guest2"
+
+    mkdir -p "$share_dir" "$share_dir2"
+    echo "hello from host" > "$share_dir/testfile.txt"
+    echo "second share" > "$share_dir2/testfile2.txt"
+
+    cat > "$work/Containerfile" <<'EOF'
+FROM alpine:latest
+CMD ["/bin/sh", "-c", "poweroff -f"]
+EOF
+
+    echo "-- Building container image (no WORKINGDIR)..."
+    if ! podman build --network=none -t "$img" -f "$work/Containerfile" >/dev/null 2>&1; then
+        report fail "--mount (podman build failed)"
+        rm -rf "$work"
+        return
+    fi
+
+    echo "-- Building slim VM..."
+    if ! "$SLIM_BIN" build qcow2 "$img" >/dev/null 2>&1; then
+        report fail "--mount (slim build failed)"
+        cleanup "$img" "$img"
+        rm -rf "$work"
+        return
+    fi
+
+    share_canon=$(readlink -f "$share_dir")
+    share_canon2=$(readlink -f "$share_dir2")
+
+    echo "-- Test 1: --mount host:guest (absolute guest path, multi-mount)..."
+    output=$(timeout "$TIMEOUT" "$SLIM_BIN" run "$img" \
+        --mount "${share_dir}:${guest_dir}" \
+        --mount "${share_dir2}:${guest_dir2}" \
+        --cmd "for f in /sys/bus/virtio/drivers/9pnet_virtio/virtio*/mount_tag; do [ -f \"\$f\" ] && echo \"\$f: \$(tr -d '\\0' < \"\$f\")\"; done; mount -v; cat ${guest_dir}/testfile.txt 2>/dev/null || echo NO_FILE; cat ${guest_dir2}/testfile2.txt 2>/dev/null || echo NO_FILE2; echo MOUNT_VERIFY_DONE; poweroff -f" \
+        2>&1 || true)
+
+    check_output "$output" "mount_tag: slim0" "--mount 9p share detected"
+    check_output "$output" "mount_tag: slim1" "--mount second 9p share detected"
+    check_output "$output" "type 9p" "--mount 9p filesystem in mount list"
+    check_output "$output" "hello from host" "--mount file accessible at guest path"
+    check_output "$output" "second share" "--mount second file accessible at guest path"
+    check_output "$output" "MOUNT_VERIFY_DONE" "--mount VM ran to completion"
+
+    cleanup "$img" "$img"
+
+    # --- Image 2: with WORKINGDIR, test relative guest path ---
+    img="slim-test-mount-wd"
+    share_dir3="$work/share3"
+
+    mkdir -p "$share_dir3"
+    echo "relative share" > "$share_dir3/relfile.txt"
+
+    cat > "$work/Containerfile.wd" <<'EOF'
+FROM alpine:latest
+WORKDIR /app
+CMD ["/bin/sh", "-c", "poweroff -f"]
+EOF
+
+    echo "-- Building container image (WORKINGDIR /app)..."
+    if ! podman build --network=none -t "$img" -f "$work/Containerfile.wd" >/dev/null 2>&1; then
+        report fail "--mount relative (podman build failed)"
+        rm -rf "$work"
+        return
+    fi
+
+    echo "-- Building slim VM..."
+    if ! "$SLIM_BIN" build qcow2 "$img" >/dev/null 2>&1; then
+        report fail "--mount relative (slim build failed)"
+        cleanup "$img" "$img"
+        rm -rf "$work"
+        return
+    fi
+
+    echo "-- Test 2: --mount host:relative-guest (resolved against WORKINGDIR)..."
+    output=$(timeout "$TIMEOUT" "$SLIM_BIN" run "$img" \
+        --mount "${share_dir3}:data" \
+        --cmd "mount -v; cat /app/data/relfile.txt 2>/dev/null || echo NO_REL_FILE; echo REL_VERIFY_DONE; poweroff -f" \
+        2>&1 || true)
+
+    check_output "$output" "type 9p" "--mount relative 9p filesystem in mount list"
+    check_output "$output" "relative share" "--mount relative file accessible at WORKINGDIR/data"
+    check_output "$output" "REL_VERIFY_DONE" "--mount relative VM ran to completion"
+
+    cleanup "$img" "$img"
+    rm -rf "$work"
+}
+
 test_service() {
    echo "=== Testing nextcloud service ==="

@@ -206,6 +303,8 @@ test_distro "archlinux" "archlinux:latest" "RUN pacman -Sy --noconfirm iproute2

 test_user

+test_mount
+
 test_service

 echo ""
@@ -8,7 +8,7 @@
 use anyhow::{Context, Result, bail};
 use base64::Engine;
 use clap::Args;
-use std::{fmt::Write as _, process::Command};
+use std::{fmt::Write as _, path::PathBuf, process::Command};

 use crate::{
    forward::PortForward,
@@ -32,6 +32,11 @@ pub struct RunCmd {
    /// cmdline as slim.cmd=<b64>). Overrides the CMD inferred at build time.
    #[clap(long)]
    cmd: Option<String>,
+
+    /// Share a host directory into the VM via 9p. The directory appears at
+    /// the same path inside the VM. Can be repeated for multiple mounts.
+    #[clap(long)]
+    mount: Vec<PathBuf>,
 }

 pub(crate) fn run(
@@ -40,6 +45,7 @@ pub(crate) fn run(
        memory,
        forward,
        cmd,
+        mount,
    }: RunCmd,
 ) -> Result<()> {
    let reg_dir = registry_dir(&name)?;
@@ -81,6 +87,27 @@ pub(crate) fn run(
        cmdline.push(format!("slim.cmd={encoded}"));
    }

+    // Build 9p shares for each --mount.  Tags are short (slim0, slim1, …)
+    // because 9p mount_tag has a ~31-byte limit.  The full destination path
+    // is passed on the kernel cmdline as slim.mount=<tag>:<base64(path)>.
+    let mut virtfs_args: Vec<String> = Vec::new();
+    for (i, host_path) in mount.iter().enumerate() {
+        let canonical = host_path
+            .canonicalize()
+            .with_context(|| format!("Cannot resolve mount path '{}'", host_path.display()))?;
+        let path_str = canonical
+            .to_str()
+            .context("Mount path is not valid UTF-8")?;
+        let tag = format!("slim{i}");
+        let dest_b64 = base64::engine::general_purpose::STANDARD.encode(path_str.as_bytes());
+
+        virtfs_args.push("-virtfs".into());
+        virtfs_args.push(format!(
+            "local,path={path_str},mount_tag={tag},security_model=mapped-xattr"
+        ));
+        cmdline.push(format!("slim.mount={tag}:{dest_b64}"));
+    }
+
    println!("Booting {name} from registry: {}", reg_dir.display());

    let cmdline = cmdline.join(" ");
@@ -101,6 +128,7 @@ pub(crate) fn run(
        .arg("-kernel")
        .arg(vmlinuz_path.as_os_str())
        .args(&fs_args)
+        .args(&virtfs_args)
        .args(["-snapshot"])
        .args(["-no-reboot"])
        .args(["-append", &cmdline])
@@ -2,6 +2,11 @@
 # slim universal init - distro-agnostic VM bootstrap.
 # Injected by `slim build` at /slim/init and invoked via init=/slim/init.

+# === Helpers ===
+b64dec() {
+    printf '%s' "$1" | base64 -d 2>/dev/null || printf '%s' "$1" | openssl base64 -d 2>/dev/null
+}
+
 # === Devices & special filesystems ===
 [ -c /dev/console ] || mknod -m 600 /dev/console c 5 1
 mkdir -p /proc /sys /dev/pts /dev/shm
@@ -34,6 +39,37 @@ ip addr add 10.0.2.15/24 dev eth0 2>/dev/null || echo "ip addr add eth0 failed"
 ip route add default via 10.0.2.2 2>/dev/null || echo "ip route add default failed"
 echo nameserver 10.0.2.3 > /etc/resolv.conf

+# === 9p shares (host directories shared via --mount) ===
+# Each share is passed as slim.mount=<tag>:<base64(guest_path)> on the
+# kernel cmdline.  The 9p tag is short (e.g. slim0) because mount_tag
+# has a ~31-byte limit; the guest path is base64-encoded.
+# Non-absolute guest paths are resolved against /slim/workdir (the
+# image's WORKINGDIR).
+SLIM_WORKDIR=""
+[ -f /slim/workdir ] && SLIM_WORKDIR=$(cat /slim/workdir 2>/dev/null)
+# shellcheck disable=SC2013 # word-splitting is intentional: cmdline tokens are space-separated
+for tok in $(cat /proc/cmdline 2>/dev/null); do
+    case "$tok" in
+        slim.mount=*)
+            v=${tok#slim.mount=}
+            tag=${v%%:*}
+            dest_b64=${v#*:}
+            dest=$(b64dec "$dest_b64") || echo "base64 decode failed"
+            if [ -n "$tag" ] && [ -n "$dest" ]; then
+                # Resolve relative paths against the image's WORKINGDIR
+                case "$dest" in
+                    /*) ;;
+                    *) dest="${SLIM_WORKDIR:-/}/${dest}" ;;
+                esac
+                mkdir -p "$dest"
+                mount -t 9p "$tag" "$dest" -o trans=virtio,version=9p2000.L 2>/dev/null \
+                    && echo "mounted 9p '$tag' -> '$dest'" \
+                    || echo "failed to mount 9p '$tag' -> '$dest'"
+            fi
+            ;;
+    esac
+done
+
 # === Drop privileges (respect USER directive from image config) ===
 # /slim/user may contain a username, uid, or uid:gid (OCI image spec).
 # Numeric uids are resolved to a username via /etc/passwd because BusyBox
@@ -75,9 +111,7 @@ for tok in $(cat /proc/cmdline 2>/dev/null); do
    case "$tok" in
        slim.cmd=*)
            v=${tok#slim.cmd=}
-            decoded=$(printf '%s' "$v" | base64 -d 2>/dev/null) \
-                || decoded=$(printf '%s' "$v" | openssl base64 -d 2>/dev/null) \
-                || echo "base64 decode failed"
+            decoded=$(b64dec "$v") || echo "base64 decode failed"
            if [ -n "$decoded" ]; then
                slim_exec "$decoded"
            fi