[pbs-devel] [PATCH proxmox-backup-restore-image] fix #4477: init: symlink busybox binaries on init

[Max Carrara]

This change makes Busybox symbolically link its inbuilt utils to their
respective locations, allowing them to be invoked through their
absolute path. This means that Busybox inbuilts like e.g. `mount`
and `env` become available at `/bin/mount` and `/usr/bin/env` etc.

In particular, when entering any of the snapshot directories in
`.zfs/snapshot` (e.g. via `cd` or `ls`), ZFS normally mounts the
respective snapshot(s) on demand, using `/usr/bin/env mount [...]`
internally. Before this change, this would fail, rendering ZFS
snapshots unavailable when restoring individual files.

Signed-off-by: Max Carrara <m.carrara at proxmox.com>
---
 src/init-shim-rs/src/main.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/init-shim-rs/src/main.rs b/src/init-shim-rs/src/main.rs
index a6e093c..083c08f 100644
--- a/src/init-shim-rs/src/main.rs
+++ b/src/init-shim-rs/src/main.rs
@@ -31,6 +31,14 @@ fn main() {
         do_mknod("/dev/null", NULL_MAJ, NULL_MIN)
     });
 
+    // tell busybox to symlink its binaries
+    wrap_err("busybox --install -s", || {
+        Command::new("/bin/busybox")
+            .args(["--install", "-s"])
+            .spawn()?;
+        Ok(())
+    });
+
     if let Err(err) = run_agetty() {
         // not fatal
         println!("[init-shim] debug: agetty start failed: {}", err);
-- 
2.30.2