IPC Namespace

Author

longjin <longjin@dragonos.org>

This page describes the current support status and future plans for IPC namespaces in DragonOS. The goal is to expose semantics consistent with Linux to users while gradually improving upon DragonOS's existing framework.

Supported Features

• Integration of IpcNamespace object with NsProxy:

  • Added IpcNamespace and connected to NsProxy, allowing each task to access its associated IPC namespace via nsproxy.ipc_ns.
  • Namespace creation/inheritance follows clone/unshare semantics:
    • Inherits the parent namespace when CLONE_NEWIPC is not included;
    • Creates an independent IPC namespace when CLONE_NEWIPC is included;
    • Mutually exclusive with CLONE_SYSVSEM, with behavior consistent with Linux.

• SysV SHM (Shared Memory) isolated by namespace:

  • Refactored the original global SHM_MANAGER into per-ns ShmManager, with all shmget/shmat/shmdt/shmctl taking effect under current.nsproxy.ipc_ns.
  • shmat/shmdt: VMA records ShmId, precisely maintaining map_count during unmapping; after IPC_RMID, physical reclamation is completed when SHM_DEST && map_count==0.
  • Basic semantics and error codes aligned: IPC_CREAT|IPC_EXCL, ENOENT, rejection of SHM_HUGETLB, etc.

• Basic test cases: (in test_ipc_ns_shm.rs)

  • After unshare(CLONE_NEWIPC), keys in parent/child namespaces are not visible;
  • Same keys across namespaces do not conflict;
  • After IPC_RMID, the same key can be recreated;
  • Outputs PASS/FAIL and summary results.

Not Yet Implemented / Planned

• /proc/[pid]/ns/ipc and setns:

  • Temporarily postponed, with only planning for read-only placeholders and the simplest setns path; permission validation and switching sequencing will be added in subsequent versions.

• Other SysV IPC subsystems:

  • msg/sem framework not yet incorporated; UNDO lists for sem and coordination with unshare/setns need to be implemented simultaneously when introduced.

• POSIX mqueue:

  • Per-ns mqueuefs kernel mounting, quotas, and sysctl not yet provided.

• Permissions and quotas:

  • ipcperms(), ns_capable(user_ns, CAP_IPC_OWNER);
  • ucounts/RLIMIT and per-ns sysctl such as /proc/sys/kernel/shm*.

Compatibility and Notes

• At this stage, only SysV SHM provides namespace isolation; other IPC types still operate under global semantics.
• Code evolves in a modular manner: when adding msg/sem/mqueue later, stability and consistency of user-side semantics will be maintained.

References

• Code locations:
  • kernel/src/process/namespace/ipc_namespace.rs
  • kernel/src/process/namespace/nsproxy.rs
  • kernel/src/ipc/syscall/ within sys_shm*
  • kernel/src/mm/ucontext/ (VMA and SHM count maintenance)