fs: nfs: Make nfs boot time y2038 safe

boot_time is represented as a struct timespec.
struct timespec and CURRENT_TIME are not y2038 safe.
Overall, the plan is to use timespec64 and ktime_t for
all internal kernel representation of timestamps.
CURRENT_TIME will also be removed.

boot_time is used to construct the nfs client boot verifier.

Use ktime_t to represent boot_time and ktime_get_real() for
the boot_time value.

Following Trond's request https://lkml.org/lkml/2016/6/9/22 ,
use ktime_t instead of converting to struct timespec64.

Use higher and lower 32 bit parts of ktime_t for the boot
verifier.

Use the lower 32 bit part of ktime_t for the authsys_parms
stamp field.

Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Cc: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: Anna Schumaker <anna.schumaker@netapp.com>
Cc: linux-nfs@vger.kernel.org
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/client.c

@@ -1082,7 +1082,7 @@ void nfs_clients_init(struct net *net)
 	idr_init(&nn->cb_ident_idr);
 #endif
 	spin_lock_init(&nn->nfs_client_lock);
-	nn->boot_time = CURRENT_TIME;
+	nn->boot_time = ktime_get_real();
 }
 
 #ifdef CONFIG_PROC_FS

fs/nfs/netns.h

@@ -29,7 +29,7 @@ struct nfs_net {
 	int cb_users[NFS4_MAX_MINOR_VERSION + 1];
 #endif
 	spinlock_t nfs_client_lock;
-	struct timespec boot_time;
+	ktime_t boot_time;
 #ifdef CONFIG_PROC_FS
 	struct proc_dir_entry *proc_nfsfs;
 #endif

fs/nfs/nfs4proc.c

@@ -5299,12 +5299,14 @@ static void nfs4_init_boot_verifier(const struct nfs_client *clp,
 	if (test_bit(NFS4CLNT_PURGE_STATE, &clp->cl_state)) {
 		/* An impossible timestamp guarantees this value
 		 * will never match a generated boot time. */
-		verf[0] = 0;
-		verf[1] = cpu_to_be32(NSEC_PER_SEC + 1);
+		verf[0] = cpu_to_be32(U32_MAX);
+		verf[1] = cpu_to_be32(U32_MAX);
 	} else {
 		struct nfs_net *nn = net_generic(clp->cl_net, nfs_net_id);
-		verf[0] = cpu_to_be32(nn->boot_time.tv_sec);
-		verf[1] = cpu_to_be32(nn->boot_time.tv_nsec);
+		u64 ns = ktime_to_ns(nn->boot_time);
+
+		verf[0] = cpu_to_be32(ns >> 32);
+		verf[1] = cpu_to_be32(ns);
 	}
 	memcpy(bootverf->data, verf, sizeof(bootverf->data));
 }

fs/nfs/nfs4xdr.c

@@ -1850,7 +1850,7 @@ static void encode_create_session(struct xdr_stream *xdr,
 	*p++ = cpu_to_be32(RPC_AUTH_UNIX);			/* auth_sys */
 
 	/* authsys_parms rfc1831 */
-	*p++ = cpu_to_be32(nn->boot_time.tv_nsec);	/* stamp */
+	*p++ = cpu_to_be32(ktime_to_ns(nn->boot_time));	/* stamp */
 	p = xdr_encode_array(p, clnt->cl_nodename, clnt->cl_nodelen);
 	*p++ = cpu_to_be32(0);				/* UID */
 	*p++ = cpu_to_be32(0);				/* GID */