NFSD: Clean up the nfsd_net::nfssvc_boot field

There are two boot-time fields in struct nfsd_net: one called
boot_time and one called nfssvc_boot. The latter is used only to
form write verifiers, but its documenting comment declares:

        /* Time of server startup */

Since commit 27c438f53e79 ("nfsd: Support the server resetting the
boot verifier"), this field can be reset at any time; it's no
longer tied to server restart. So that comment is stale.

Also, according to pahole, struct timespec64 is 16 bytes long on
x86_64. The nfssvc_boot field is used only to form a write verifier,
which is 8 bytes long.

Let's clarify this situation by manufacturing an 8-byte verifier
in nfs_reset_boot_verifier() and storing only that in struct
nfsd_net.

We're grabbing 128 bits of time, so compress all of those into a
64-bit verifier instead of throwing out the high-order bits.
In the future, the siphash_key can be re-used for other hashed
objects per-nfsd_net.

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

1 files changed, 5 insertions, 3 deletions

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 9e8b77d2a3a4..a6ed30025984 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -11,6 +11,7 @@
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
 #include <linux/percpu_counter.h>
+#include <linux/siphash.h>
 
 /* Hash tables for nfs4_clientid state */
 #define CLIENT_HASH_BITS                 4
@@ -108,9 +109,8 @@ struct nfsd_net {
 	bool nfsd_net_up;
 	bool lockd_up;
 
-	/* Time of server startup */
-	struct timespec64 nfssvc_boot;
-	seqlock_t boot_lock;
+	seqlock_t writeverf_lock;
+	unsigned char writeverf[8];
 
 	/*
 	 * Max number of connections this nfsd container will allow. Defaults
@@ -187,6 +187,8 @@ struct nfsd_net {
 	char			nfsd_name[UNX_MAXNODENAME+1];
 
 	struct nfsd_fcache_disposal *fcache_disposal;
+
+	siphash_key_t		siphash_key;
 };
 
 /* Simple check to find out if a given net was properly initialized */