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composefs-backend: Implement bootc usr-overlay #1643

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Merged
merged 1 commit into from
Sep 25, 2025
Merged

composefs-backend: Implement bootc usr-overlay #1643

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4 changes: 3 additions & 1 deletion crates/initramfs/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -179,7 +179,9 @@ fn overlay_state(base: impl AsFd, state: impl AsFd, source: &str) -> Result<()>
mount_at_wrapper(fs, base, ".").context("Moving mount")
}

fn overlay_transient(base: impl AsFd) -> Result<()> {
/// Mounts a transient overlayfs with passed in fd as the lowerdir
#[context("Mounting transient overlayfs")]
pub fn overlay_transient(base: impl AsFd) -> Result<()> {
overlay_state(base, prepare_mount(mount_tmpfs()?)?, "transient")
}

Expand Down
25 changes: 25 additions & 0 deletions crates/lib/src/bootc_composefs/state.rs
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Expand Up @@ -2,10 +2,13 @@ use std::os::unix::fs::symlink;
use std::{fs::create_dir_all, process::Command};

use anyhow::{Context, Result};
use bootc_initramfs_setup::overlay_transient;
use bootc_kernel_cmdline::utf8::Cmdline;
use bootc_mount::tempmount::TempMount;
use bootc_utils::CommandRunExt;
use camino::Utf8PathBuf;
use cap_std_ext::cap_std::ambient_authority;
use cap_std_ext::cap_std::fs::Dir;
use cap_std_ext::{cap_std, dirext::CapStdExtDirExt};
use composefs::fsverity::{FsVerityHashValue, Sha256HashValue};
use fn_error_context::context;
Expand Down Expand Up @@ -163,3 +166,25 @@ pub(crate) fn write_composefs_state(

Ok(())
}

pub(crate) fn composefs_usr_overlay() -> Result<()> {
let usr = Dir::open_ambient_dir("/usr", ambient_authority()).context("Opening /usr")?;
let is_usr_mounted = usr
.is_mountpoint(".")
.context("Failed to get mount details for /usr")?;

let is_usr_mounted =
is_usr_mounted.ok_or_else(|| anyhow::anyhow!("Falied to get mountinfo"))?;

if is_usr_mounted {
println!("A writeable overlayfs is already mounted on /usr");
return Ok(());
}

overlay_transient(usr)?;

println!("A writeable overlayfs is now mounted on /usr");
println!("All changes there will be discarded on reboot.");

Ok(())
}
13 changes: 12 additions & 1 deletion crates/lib/src/cli.rs
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Expand Up @@ -33,6 +33,7 @@ use serde::{Deserialize, Serialize};
use crate::bootc_composefs::{
finalize::{composefs_native_finalize, get_etc_diff},
rollback::composefs_rollback,
state::composefs_usr_overlay,
status::composefs_booted,
switch::switch_composefs,
update::upgrade_composefs,
Expand Down Expand Up @@ -1289,7 +1290,17 @@ async fn run_from_opt(opt: Opt) -> Result<()> {
Ok(())
}
Opt::Edit(opts) => edit(opts).await,
Opt::UsrOverlay => usroverlay().await,
Opt::UsrOverlay => {
#[cfg(feature = "composefs-backend")]
if composefs_booted()?.is_some() {
composefs_usr_overlay()
} else {
usroverlay().await
}

#[cfg(not(feature = "composefs-backend"))]
usroverlay().await
}
Comment on lines +1293 to +1303
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medium

The conditional compilation logic here is a bit redundant. The else branch for when composefs-backend is enabled is identical to the case where it's disabled. You can simplify this to improve readability and reduce duplication.

        Opt::UsrOverlay => {
            #[cfg(feature = "composefs-backend")]
            if composefs_booted()?.is_some() {
                return composefs_usr_overlay();
            }
            usroverlay().await
        }

Opt::Container(opts) => match opts {
ContainerOpts::Lint {
rootfs,
Expand Down