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From:   Nagendra Tomar <Nagendra.Tomar@microsoft.com>
To:     "anna.schumaker@netapp.com" <anna.schumaker@netapp.com>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: RE: [PATCH v3 0/5] SUNRPC: Create sysfs files for changing IP address
Thread-Topic: [PATCH v3 0/5] SUNRPC: Create sysfs files for changing IP
 address
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Hi Anna,
     We have a similar but slightly different requirement.
You change allows a user to force a xprt's remote address to anything, allo=
wing
it to connect to a different address than what it originally had.
The original server/xprt address starts as the one that userspace mount pro=
gram
provides, possibly after resolving the servername used in the mount command=
.

Our requirement is that that server name remains same but its address chang=
es,=20
aka, DNS failover.
Such cases (which I believe are more common) can be handled fully automatic=
ally,
by resolving the server name before every xprt reconnect. CIFS does this.
NFS also has fs/nfs/dns_resolve.c which we can use to do the name resolutio=
n,
though it's currently not being used for this specific use.

Did you have a similar requirement in mind, and/or did you consider the abo=
ve?
Would like to know your thoughts.

Thanks,
Tomar

-----Original Message-----
From: Anna Schumaker <schumakeranna@gmail.com> On Behalf Of schumaker.anna@=
gmail.com
Sent: 13 March 2021 02:48
To: linux-nfs@vger.kernel.org
Cc: Anna.Schumaker@Netapp.com
Subject: [PATCH v3 0/5] SUNRPC: Create sysfs files for changing IP address

From: Anna Schumaker <Anna.Schumaker@Netapp.com>

It's possible for an NFS server to go down but come back up with a
different IP address. These patches provide a way for administrators to
handle this issue by providing a new IP address for xprt sockets to
connect to.

Chuck has suggested some ideas for future work that could also use this
interface, such as:
- srcaddr: To move between network devices on the client
- type: "tcp", "rdma", "local"
- bound: 0 for autobind, or the result of the most recent rpcbind query
- connected: either true or false
- last: read-only timestamp of the last operation to use the transport
- device: A symlink to the physical network device

Changes in v3:
- Rename functions and objects to make future expansion easier
- Put files under /sys/kernel/sunrpc/client/ instead of
  /sys/kernel/sunrpc/net/, again for future expansions
- Clean up use of WARN_ON_ONCE() in xs_connect()
- Fix up locking, reference counting, and RCU usage
- Unconditionally create files so userspace tools don't need to guess
  what is supported (We return an error message now instead)

Changes in v2:
- Put files under /sys/kernel/sunrpc/ instead of /sys/net/sunrpc/
- Rename file from "address" to "dstaddr"

Thoughts?
Anna


Anna Schumaker (5):
  sunrpc: Create a sunrpc directory under /sys/kernel/
  sunrpc: Create a client/ subdirectory in the sunrpc sysfs
  sunrpc: Create per-rpc_clnt sysfs kobjects
  sunrpc: Prepare xs_connect() for taking NULL tasks
  sunrpc: Create a per-rpc_clnt file for managing the destination IP
    address

 include/linux/sunrpc/clnt.h |   1 +
 net/sunrpc/Makefile         |   2 +-
 net/sunrpc/clnt.c           |   5 +
 net/sunrpc/sunrpc_syms.c    |   8 ++
 net/sunrpc/sysfs.c          | 191 ++++++++++++++++++++++++++++++++++++
 net/sunrpc/sysfs.h          |  20 ++++
 net/sunrpc/xprtsock.c       |   2 +-
 7 files changed, 227 insertions(+), 2 deletions(-)
 create mode 100644 net/sunrpc/sysfs.c
 create mode 100644 net/sunrpc/sysfs.h

--=20
2.29.2