NFS: Add ability to send MOUNTPROC_UMNT to the kernel's mountd client

After certain failure modes of an NFS mount, an NFS client should send
a MOUNTPROC_UMNT request to remove the just-added mount entry from the
server's mount table.  While no-one should rely on the accuracy of the
server's mount table, sending a UMNT is simply being a good internet
neighbor.

Since NFS mount processing is handled in the kernel now, we will need
a function in the kernel's mountd client that can post a MOUNTRPC_UMNT
request, in order to handle these failure modes.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 80 insertions, 0 deletions

diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index 7dd90a6769d..8d2b71d57d2 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -102,6 +102,7 @@ struct nfs_mount_request {
 };
 
 extern int nfs_mount(struct nfs_mount_request *info);
+extern void nfs_umount(const struct nfs_mount_request *info);
 
 /* client.c */
 extern struct rpc_program nfs_program;
diff --git a/fs/nfs/mount_clnt.c b/fs/nfs/mount_clnt.c
index 38ef9eaec40..72dd8b6ccaf 100644
--- a/fs/nfs/mount_clnt.c
+++ b/fs/nfs/mount_clnt.c
@@ -209,6 +209,71 @@ out_mnt_err:
         goto out;
 }
 
+/**
+ * nfs_umount - Notify a server that we have unmounted this export
+ * @info: pointer to umount request arguments
+ *
+ * MOUNTPROC_UMNT is advisory, so we set a short timeout, and always
+ * use UDP.
+ */
+void nfs_umount(const struct nfs_mount_request *info)
+{
+        static const struct rpc_timeout nfs_umnt_timeout = {
+                .to_initval = 1 * HZ,
+                .to_maxval = 3 * HZ,
+                .to_retries = 2,
+        };
+        struct rpc_create_args args = {
+                .protocol       = IPPROTO_UDP,
+                .address        = info->sap,
+                .addrsize       = info->salen,
+                .timeout        = &nfs_umnt_timeout,
+                .servername     = info->hostname,
+                .program        = &mnt_program,
+                .version        = info->version,
+                .authflavor     = RPC_AUTH_UNIX,
+                .flags          = RPC_CLNT_CREATE_NOPING,
+        };
+        struct mountres result;
+        struct rpc_message msg  = {
+                .rpc_argp       = info->dirpath,
+                .rpc_resp       = &result,
+        };
+        struct rpc_clnt *clnt;
+        int status;
+
+        if (info->noresvport)
+                args.flags |= RPC_CLNT_CREATE_NONPRIVPORT;
+
+        clnt = rpc_create(&args);
+        if (unlikely(IS_ERR(clnt)))
+                goto out_clnt_err;
+
+        dprintk("NFS: sending UMNT request for %s:%s\n",
+                (info->hostname ? info->hostname : "server"), info->dirpath);
+
+        if (info->version == NFS_MNT3_VERSION)
+                msg.rpc_proc = &clnt->cl_procinfo[MOUNTPROC3_UMNT];
+        else
+                msg.rpc_proc = &clnt->cl_procinfo[MOUNTPROC_UMNT];
+
+        status = rpc_call_sync(clnt, &msg, 0);
+        rpc_shutdown_client(clnt);
+
+        if (unlikely(status < 0))
+                goto out_call_err;
+
+        return;
+
+out_clnt_err:
+        dprintk("NFS: failed to create UMNT RPC client, status=%ld\n",
+                        PTR_ERR(clnt));
+        return;
+
+out_call_err:
+        dprintk("NFS: UMNT request failed, status=%d\n", status);
+}
+
 /*
  * XDR encode/decode functions for MOUNT
  */
@@ -407,6 +472,13 @@ static struct rpc_procinfo mnt_procedures[] = {
                 .p_statidx      = MOUNTPROC_MNT,
                 .p_name         = "MOUNT",
         },
+        [MOUNTPROC_UMNT] = {
+                .p_proc         = MOUNTPROC_UMNT,
+                .p_encode       = (kxdrproc_t)mnt_enc_dirpath,
+                .p_arglen       = MNT_enc_dirpath_sz,
+                .p_statidx      = MOUNTPROC_UMNT,
+                .p_name         = "UMOUNT",
+        },
 };
 
 static struct rpc_procinfo mnt3_procedures[] = {
@@ -419,6 +491,13 @@ static struct rpc_procinfo mnt3_procedures[] = {
                 .p_statidx      = MOUNTPROC3_MNT,
                 .p_name         = "MOUNT",
         },
+        [MOUNTPROC3_UMNT] = {
+                .p_proc         = MOUNTPROC3_UMNT,
+                .p_encode       = (kxdrproc_t)mnt_enc_dirpath,
+                .p_arglen       = MNT_enc_dirpath_sz,
+                .p_statidx      = MOUNTPROC3_UMNT,
+                .p_name         = "UMOUNT",
+        },
 };