install: Fix broken warn_on_host_root check

The `warn_on_host_root` check was broken when we added support for
installing on already-ostree systems (but only for already-ostree
systems).

See #907

The solution is to use the original user provided root_path for the fd
passed to warn_on_host_root, rather than the modified one, as that will
always match /proc/0/root's fsid (in ostree systems systemd is running
with the deployment root as its root, and this is what we have mounted
as /:/target)

Signed-off-by: Omer Tuchfeld <[email protected]>

lib/src/install.rs

@@ -1716,6 +1716,14 @@ pub(crate) async fn install_to_filesystem(
         }
     }
 
+    // Check to see if this happens to be the real host root
+    if !fsopts.acknowledge_destructive {
+        let root_path = &fsopts.root_path;
+        let rootfs_fd = Dir::open_ambient_dir(root_path, cap_std::ambient_authority())
+            .with_context(|| format!("Opening target root directory {root_path}"))?;
+        warn_on_host_root(&rootfs_fd)?;
+    }
+
     // If we're installing to an ostree root, then find the physical root from
     // the deployment root.
     let possible_physical_root = fsopts.root_path.join("sysroot");
@@ -1741,11 +1749,6 @@ pub(crate) async fn install_to_filesystem(
         rootfs_fd
     };
 
-    // Check to see if this happens to be the real host root
-    if !fsopts.acknowledge_destructive {
-        warn_on_host_root(&rootfs_fd)?;
-    }
-
     match fsopts.replace {
         Some(ReplaceMode::Wipe) => {
             let rootfs_fd = rootfs_fd.try_clone()?;