register managed namespaces with symlinks

src/namespace/mod.rs

@@ -5,8 +5,9 @@ use crate::link::{LinkError, link_up_ns};
 use crate::namespace::raw::{NamespaceSetupError, create_network_namespace};
 use nix::errno::Errno;
 use nix::mount::{MntFlags, MsFlags, mount, umount2};
-use std::fs::{File, create_dir_all, remove_file};
+use std::fs::{File, create_dir, remove_file};
 use std::io::{Error as IoError, ErrorKind};
+use std::os::unix::fs::symlink;
 use std::path::{Path, PathBuf};
 use thiserror::Error;
 use tracing::{debug, error, info};
@@ -20,13 +21,25 @@ impl NetNs {
     /// Create a new named network namespace that will be removed when dropped
     pub fn new(name: NamespaceName) -> Result<Self, NamespaceError> {
         let parent = Path::new("/var/run/netns");
-        create_dir_all(parent).map_err(NamespaceError::Parent)?;
+        let nsd_parent = Path::new("/var/run/netnsd");
+        setup_tmpfs(parent)?;
+        setup_tmpfs(nsd_parent)?;
+
         let path = parent.join(&name);
+        let nsd_path = nsd_parent.join(&name);
 
         match File::create_new(&path) {
             Ok(_) => {}
             Err(e) if e.kind() == ErrorKind::AlreadyExists => {
                 info!(%name, "using existing network namespace");
+
+                if !nsd_path.is_symlink() {
+                    symlink(&path, &nsd_path).map_err(|error| NamespaceError::Symlink {
+                        error,
+                        path: nsd_path.clone(),
+                    })?;
+                }
+
                 return Ok(NetNs {
                     name: name.clone(),
                     path,
@@ -38,6 +51,12 @@ impl NetNs {
 
         let ns = create_network_namespace(move |ns| {
             bind_namespace(&ns, &path)?;
+            if !nsd_path.is_symlink() {
+                symlink(&path, &nsd_path).map_err(|error| NamespaceError::Symlink {
+                    error,
+                    path: nsd_path.clone(),
+                })?;
+            }
             Result::<_, NamespaceError>::Ok(NetNs { name, path })
         })?;
 
@@ -47,6 +66,31 @@ impl NetNs {
     }
 }
 
+fn setup_tmpfs(path: &Path) -> Result<(), NamespaceError> {
+    let created = match create_dir(path) {
+        Ok(_) => Ok(true),
+        Err(error) if error.kind() == ErrorKind::AlreadyExists => Ok(false),
+        Err(error) => Err(NamespaceError::Parent {
+            path: path.into(),
+            error,
+        }),
+    }?;
+    if created {
+        mount(
+            Some("tmpfs"),
+            path.as_os_str(),
+            Some("tmpfs"),
+            MsFlags::empty(),
+            Some("size=16k,mode=1755"),
+        )
+        .map_err(|error| NamespaceError::ParentTmpfs {
+            path: path.into(),
+            error,
+        })?
+    }
+    Ok(())
+}
+
 fn bind_namespace(namespace: &Path, path: &Path) -> Result<(), NamespaceError> {
     debug!(namespace = %namespace.display(), path = %path.display(), "mounting namespace");
     mount(
@@ -75,7 +119,7 @@ impl NetNs {
         umount2(&self.path, MntFlags::MNT_DETACH).map_err(NamespaceError::UnMount)?;
         remove_file(&self.path).map_err(|error| NamespaceError::Delete {
             error,
-            path: self.path
+            path: self.path,
         })?;
         Ok(())
     }
@@ -83,12 +127,16 @@ impl NetNs {
 
 #[derive(Debug, Error)]
 pub enum NamespaceError {
-    #[error("Failed to create parent directory for namespaces (/var/run/netns): {0:#}")]
-    Parent(IoError),
+    #[error("Failed to create parent directory for namespaces {}: {error:#}", path.display())]
+    Parent { path: PathBuf, error: IoError },
+    #[error("Failed to create parent tmpfs for namespaces {}: {error:#}", path.display())]
+    ParentTmpfs { path: PathBuf, error: Errno },
     #[error("Failed to create namespace file {}: {error:#}", path.display())]
     Create { path: PathBuf, error: IoError },
     #[error("Failed to delete namespace file {}: {error:#}", path.display())]
     Delete { path: PathBuf, error: IoError },
+    #[error("Failed to register namespace symlink {}: {error:#}", path.display())]
+    Symlink { path: PathBuf, error: IoError },
     #[error("Failed to setup namespace: {0:#}")]
     Setup(#[from] NamespaceSetupError),
     #[error("Failed to bind-mount netns handle: {0:?}")]