Detect group mount points by parsing /proc/mounts

north.toml

@@ -7,8 +7,8 @@ data_dir = "target/north/data"
 key_dir = "target/north/keys"
 
 [cgroups]
-memory = "/sys/fs/cgroup/memory/north"
-cpu = "/sys/fs/cgroup/cpu/north"
+memory = "north"
+cpu = "north"
 
 [devices]
 unshare_root = "/"

north/Cargo.toml

@@ -30,6 +30,7 @@ minijail = { path  = "../minijail/minijail" }
 nix = "0.17.0"
 north_common = { path = "../north_common" }
 prettytable-rs = { version = "0.8.0", default-features = false }
+proc-mounts = "0.2.4"
 regex = "1.3.9"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0.56"

north/src/linux/cgroups.rs

@@ -24,6 +24,7 @@ use async_std::{
 use futures::{future::FutureExt, select};
 use log::{debug, warn};
 use north_common::manifest;
+use proc_mounts::MountIter;
 use std::time::Duration;
 
 const LIMIT_IN_BYTES: &str = "memory.limit_in_bytes";
@@ -76,7 +77,9 @@ impl CGroup for CGroupMem {
 
 impl CGroupMem {
     pub async fn new(name: &str, cgroup: &manifest::CGroupMem, tx: EventTx) -> Result<CGroupMem> {
-        let path = SETTINGS.cgroups.memory.join(name);
+        let mount_point =
+            get_mount_point("memory").context("Failed to detect cgroups memory mount point")?;
+        let path = mount_point.join(SETTINGS.cgroups.memory.join(name));
         create(&path).await?;
 
         // Configure memory limit
@@ -151,7 +154,9 @@ impl CGroup for CGroupCpu {
 
 impl CGroupCpu {
     pub async fn new(name: &str, cgroup: &manifest::CGroupCpu) -> Result<CGroupCpu> {
-        let path = SETTINGS.cgroups.cpu.join(name);
+        let mount_point =
+            get_mount_point("cpu").context("Failed to detect cgroups cpu mount point")?;
+        let path = mount_point.join(SETTINGS.cgroups.cpu.join(name));
         create(&path).await?;
 
         // Configure cpu shares
@@ -247,3 +252,13 @@ async fn write(path: &Path, value: &str) -> Result<()> {
         .with_context(|| format!("Failed sync {}", path.display()))?;
     Ok(())
 }
+
+fn get_mount_point(cgroup: &str) -> Result<PathBuf> {
+    let cgroup = String::from(cgroup);
+    MountIter::new()
+        .context("Cannot access mount points")?
+        .filter_map(|m| m.ok())
+        .find(|m| m.fstype == "cgroup" && m.options.contains(&cgroup))
+        .map(|m| m.dest.into())
+        .ok_or_else(|| anyhow!("No mount point for cgroup {}", &cgroup))
+}

north/src/settings.rs

@@ -183,13 +183,13 @@ struct CliOptions {
     #[structopt(long)]
     pub unshare_fstype: Option<String>,
 
-    /// CGroups Memory dir. This can be a subdir of the root memory cgroup.
+    /// CGroups Memory dir. This is the subdir added to the root memory cgroup.
     /// The directory is created if it does not exist.
     /// This groups acts as the toplevel north memory cgroup.
     #[structopt(long)]
     pub cgroup_memory: Option<PathBuf>,
 
-    /// CGroups CPU dir. This can be a subdir of the root memory cgroup.
+    /// CGroups CPU dir. This is the subdir added to the root cpu cgroup.
     /// The directory is created if it does not exist.
     /// This groups acts as the toplevel north cpu cgroup.
     #[structopt(long)]