[RFC PATCH 0/5] SUNRPC: "RPC pipefs per network namespace" preparations

[Stanislav Kinsbursky <skinsbursky@parallels.com>]

Hello to everyone. 
RPC pipefs file system have to work per network namespace context is required
prior to any NFS modifications.
This is a way how to do it. I'll really appreciate for any comments.

There are several statements about how to make RPC pipefs working per network
namespace context.
Here they are:
1) RPC pipefs should be mounted per network namespace context.
2) RPC pipefs superblock should holds network namespace while active.
3) RPC pipefs lookup and readir should be perfomed in network namespace context
it was mounted. IOW, user-space process, working in another network namespace
context, should see RPC pipefs dentries from network namespace context this
mount-point was created (like it was done for sysfs). 

These statement leads to some restrictions which we must follow during
implementation. Here are they:
1) RPC pipefs mount can't be performed in kernel context since new super block
will holds networks namespace reference and it's impossible to recognize, when
and how we have to release this mount point. IOW rpc_get_mount() and
rpc_put_mount() have to be removed.
2) RPC pipefs should provide some new helpers to lookup directory dentry for
those modules which creates pipes, because without RPC pipefs mount point
general lookup can't be performed.
3) These methods must garantee, that pipefs superblock will be active during
pipes creation and destruction.

So, here is the idea of making RPC pipefs works per network namespace context:
1) RPC pipefs superblock should holds network namespcae context while active.
2) RPC pipefs should send notification events on superblock creation and
destruction.
3) RPC pipefs should provide "lookup dentry by name" method for notification
subscribers.
4) RPC pipefs should place superblock reference on current network namespace
context on creation and remove it on destruction.
5) RPC pipefs should provide safe "lookup dentry by name" method for per-net
operations, which garantees, that superblock is active, while
per-net-operations are performing.
6) Client and cache directories creation and destruction should be performed
also on superblock creation and destruction notification events. Note: generic
creation (like now) can fail (if no superblock is not created yet).
7) Pipes creation and destruction should be performed on superblock creation
and destruction events. Also pipes operations should be performed during
per-net operation and in this case they could fail (due to the same reason as
in statement above).

This patch-set implements first 5 points and thus doesn't affects current RPC
pipefs logic.

The only problem about I'm not sure how to solve properly yet, is auth gss
pipes creations operations. Hoping for some help with it.


The following series consists of:

---

Stanislav Kinsbursky (5):
      SUNRPC: hold current network namespace while pipefs superblock is active
      SUNRPC: send notification events on pipefs sb creation and destruction
      SUNRPC: pipefs dentry lookup helper introduced
      SUNRPC: put pipefs superblock link on network namespace
      SUNRPC: pipefs per-net operations helper introduced


 include/linux/sunrpc/rpc_pipe_fs.h |   16 ++++++
 net/sunrpc/netns.h                 |    3 +
 net/sunrpc/rpc_pipe.c              |  103 ++++++++++++++++++++++++++++++++++++
 net/sunrpc/sunrpc_syms.c           |    1 
 4 files changed, 122 insertions(+), 1 deletions(-)

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