[ABI REVIEW][PATCH 0/8] Namespace file descriptors

[Eric W. Biederman]

Introduce file for manipulating namespaces and related syscalls.
files:
/proc/self/ns/<nstype>

syscalls:
int setns(unsigned long nstype, int fd);
socketat(int nsfd, int family, int type, int protocol);

Netlink attribute:
IFLA_NS_FD int fd.

Name space file descriptors address three specific problems that
can make namespaces hard to work with.
- Namespaces require a dedicated process to pin them in memory.
- It is not possible to use a namespace unless you are the child of the
  original creator.
- Namespaces don't have names that userspace can use to talk about them.

Opening of the /proc/self/ns/<nstype> files return a file descriptor
that can be used to talk about a specific namespace, and to keep the
specified namespace alive.

/proc/self/ns/<nstype> can be bind mounted as:
mount --bind /proc/self/ns/net /some/filesystem/path
to keep the namespace alive as long as the mount exists.

setns() as a companion to unshare allows changing the namespace
of the current process, being able to unshare the namespace is
a requirement.

There are two primary envisioned uses for this functionality.
o ``Entering'' an existing container.
o Allowing multiple network namespaces to be in use at once on
  the same machine, without requiring elaborate infrastructure.

Overall this received positive reviews on the containers list but this
needs a wider review of the ABI as this is pretty fundamental kernel
functionality.


I have left out the pid namespaces bits for the moment because the pid
namespace still needs work before it is safe to unshare, and my concern
at the moment is ensuring the system calls seem reasonable.

Eric W. Biederman (8):
      ns: proc files for namespace naming policy.
      ns: Introduce the setns syscall
      ns proc: Add support for the network namespace.
      ns proc: Add support for the uts namespace
      ns proc: Add support for the ipc namespace
      ns proc: Add support for the mount namespace
      net: Allow setting the network namespace by fd
      net: Implement socketat.

---
 fs/namespace.c              |   57 +++++++++++++
 fs/proc/Makefile            |    1 +
 fs/proc/base.c              |   22 +++---
 fs/proc/inode.c             |    7 ++
 fs/proc/internal.h          |   18 ++++
 fs/proc/namespaces.c        |  193 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/if_link.h     |    1 +
 include/linux/proc_fs.h     |   20 +++++
 include/net/net_namespace.h |    1 +
 ipc/namespace.c             |   31 +++++++
 kernel/nsproxy.c            |   39 +++++++++
 kernel/utsname.c            |   32 +++++++
 net/core/net_namespace.c    |   56 +++++++++++++
 net/core/rtnetlink.c        |    4 +-
 net/socket.c                |   26 ++++++-
 15 files changed, 494 insertions(+), 14 deletions(-)

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