From 8e341d6005deabbf25a807c4fa99031072388ebc Mon Sep 17 00:00:00 2001
From: Bruce Leidl <bruce@subgraph.com>
Date: Sun, 6 Jan 2019 18:15:44 -0500
Subject: [PATCH] Mount tmpfs overlay over rootfs if citadel.overlay is set

---
 citadel-mount/src/main.rs | 34 ++++++++++++++++++++++++++++++++--
 libcitadel/src/cmdline.rs |  2 ++
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/citadel-mount/src/main.rs b/citadel-mount/src/main.rs
index 07f4780..ca46698 100644
--- a/citadel-mount/src/main.rs
+++ b/citadel-mount/src/main.rs
@@ -5,8 +5,9 @@ extern crate libc;
 
 use std::process::exit;
 use std::env;
+use std::fs;
 
-use libcitadel::{Result,CommandLine,set_verbose,format_error,ResourceImage};
+use libcitadel::{Result,CommandLine,set_verbose,format_error,ResourceImage,util};
 
 
 mod boot_select;
@@ -20,7 +21,7 @@ use rootfs::Rootfs;
 ///   citadel-mount rootfs
 ///   citadel-mount kernel
 ///   citadel-mount extra
-///   citadel-mount copy-artifacts
+///   citadel-mount overlay
 ///
 /// 'rootfs' creates the /dev/mapper/rootfs device which will be mounted as root filesystem
 ///
@@ -41,6 +42,7 @@ fn main() {
         Some(ref s) if s == "rootfs" => mount_rootfs(),
         Some(ref s) if s == "kernel" => mount_kernel(),
         Some(ref s) if s == "extra" => mount_extra(),
+        Some(ref s) if s == "overlay" => mount_overlay(),
         _ => Err(format_err!("Bad or missing argument")),
     };
 
@@ -69,3 +71,31 @@ fn mount_extra() -> Result<()> {
     image.mount()?;
     Ok(())
 }
+
+fn mount_overlay() -> Result<()> {
+    if !CommandLine::overlay() {
+        info!("Not mounting rootfs overlay because citadel.overlay is not enabled");
+        return Ok(())
+    }
+    info!("Creating rootfs overlay");
+
+    info!("Moving /sysroot mount to /rootfs.ro");
+    fs::create_dir_all("/rootfs.ro")?;
+    util::exec_cmdline("/usr/bin/mount", "--make-private /")?;
+    util::exec_cmdline("/usr/bin/mount", "--move /sysroot /rootfs.ro")?;
+    info!("Mounting tmpfs on /rootfs.rw");
+    fs::create_dir_all("/rootfs.rw")?;
+    util::exec_cmdline("/usr/bin/mount", "-t tmpfs -orw,noatime,mode=755 rootfs.rw /rootfs.rw")?;
+    info!("Creating /rootfs.rw/work /rootfs.rw/upperdir");
+    fs::create_dir_all("/rootfs.rw/upperdir")?;
+    fs::create_dir_all("/rootfs.rw/work")?;
+    info!("Mounting overlay on /sysroot");
+    util::exec_cmdline("/usr/bin/mount", "-t overlay overlay -olowerdir=/rootfs.ro,upperdir=/rootfs.rw/upperdir,workdir=/rootfs.rw/work /sysroot")?;
+
+    info!("Moving /rootfs.ro and /rootfs.rw to new root");
+    fs::create_dir_all("/sysroot/rootfs.ro")?;
+    fs::create_dir_all("/sysroot/rootfs.rw")?;
+    util::exec_cmdline("/usr/bin/mount", "--move /rootfs.ro /sysroot/rootfs.ro")?;
+    util::exec_cmdline("/usr/bin/mount", "--move /rootfs.rw /sysroot/rootfs.rw")?;
+    Ok(())
+}
diff --git a/libcitadel/src/cmdline.rs b/libcitadel/src/cmdline.rs
index df610fe..fe3d786 100644
--- a/libcitadel/src/cmdline.rs
+++ b/libcitadel/src/cmdline.rs
@@ -60,6 +60,8 @@ impl CommandLine {
         CommandLine::var_exists("citadel.recovery")
     }
 
+    pub fn overlay() -> bool { CommandLine::var_exists("citadel.overlay") }
+
     pub fn channel() -> Option<&'static str> {
         CommandLine::get_value("citadel.channel")
     }