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ephemeral: Add writable tmpfs overlay over /root/.ssh #334

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ephemeral: Add writable tmpfs overlay over /root/.ssh #334

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12 changes: 12 additions & 0 deletions crates/kit/src/cpio.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -78,6 +78,10 @@ pub fn create_initramfs_units_cpio() -> io::Result<Vec<u8>> {
"usr/lib/systemd/system/bcvk-journal-stream.service",
include_bytes!("units/bcvk-journal-stream.service"),
),
File(
"usr/lib/systemd/system/bcvk-root-ssh-overlay.service",
include_bytes!("units/bcvk-root-ssh-overlay.service"),
),
// Drop-in to pull sysroot.mount into initrd-root-fs.target. Without
// this, nothing in the dependency graph actually requests the mount;
// dracut-rootfs-generator normally creates an
Expand All @@ -100,6 +104,10 @@ pub fn create_initramfs_units_cpio() -> io::Result<Vec<u8>> {
"usr/lib/systemd/system/initrd-fs.target.d/bcvk-copy-units.conf",
b"[Unit]\nWants=bcvk-copy-units.service\n",
),
File(
"usr/lib/systemd/system/initrd-fs.target.d/bcvk-root-ssh-overlay.conf",
b"[Unit]\nWants=bcvk-root-ssh-overlay.service\n",
),
];

let mut buf = Vec::new();
Expand Down Expand Up @@ -195,6 +203,7 @@ mod tests {
assert!(names.contains(&"usr/lib/systemd/system/bcvk-var-ephemeral.service"));
assert!(names.contains(&"usr/lib/systemd/system/bcvk-copy-units.service"));
assert!(names.contains(&"usr/lib/systemd/system/bcvk-journal-stream.service"));
assert!(names.contains(&"usr/lib/systemd/system/bcvk-root-ssh-overlay.service"));

// initrd-root-fs.target drop-in
assert!(names.contains(&"usr/lib/systemd/system/initrd-root-fs.target.d/bcvk-sysroot.conf"));
Expand All @@ -205,6 +214,9 @@ mod tests {
names.contains(&"usr/lib/systemd/system/initrd-fs.target.d/bcvk-var-ephemeral.conf")
);
assert!(names.contains(&"usr/lib/systemd/system/initrd-fs.target.d/bcvk-copy-units.conf"));
assert!(
names.contains(&"usr/lib/systemd/system/initrd-fs.target.d/bcvk-root-ssh-overlay.conf")
);

// Verify file modes: all entries are either regular files (0644) or directories
for (name, _size, mode) in &entries {
Expand Down
20 changes: 20 additions & 0 deletions crates/kit/src/units/bcvk-root-ssh-overlay.service
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Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
[Unit]
Description=Setup ephemeral /root/.ssh overlay
DefaultDependencies=no
ConditionPathExists=/etc/initrd-release
ConditionPathIsSymbolicLink=!/sysroot/root
Before=initrd-fs.target
# Must run after sysroot.mount and initrd-parse-etc.service
After=sysroot.mount initrd-parse-etc.service
Requires=sysroot.mount

[Service]
Type=oneshot
RemainAfterExit=yes
TimeoutStartSec=30
# Bind-mount /sysroot/root/.ssh to a separate location first, then use that as lowerdir.
# Using /sysroot/root/.ssh as both lowerdir and mount destination can hang on older kernels.
ExecStart=/usr/bin/mkdir -m 0700 -p /run/root-ssh-lower /run/root-ssh-upper /run/root-ssh-work
ExecStart=/usr/bin/mount --bind /sysroot/root/.ssh /run/root-ssh-lower
# Use index=off,metacopy=off to avoid extended attr operations on virtiofs
ExecStart=/usr/bin/mount -t overlay overlay -o lowerdir=/run/root-ssh-lower,upperdir=/run/root-ssh-upper,workdir=/run/root-ssh-work,index=off,metacopy=off /sysroot/root/.ssh