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>
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 8b30cdf..ed7da82 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -5299,12 +5299,14 @@
 	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));
 }