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, 2 insertions, 1 deletions

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index a8ad71567fc7..b9f27fbcd768 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1483,7 +1483,8 @@ static __net_init int nfsd_init_net(struct net *net)
 	nn->clientid_counter = nn->clientid_base + 1;
 	nn->s2s_cp_cl_id = nn->clientid_counter++;
 
-	seqlock_init(&nn->boot_lock);
+	get_random_bytes(&nn->siphash_key, sizeof(nn->siphash_key));
+	seqlock_init(&nn->writeverf_lock);
 
 	return 0;