NSM: Support IPv6 version of mon_name

The "mon_name" argument of the NSMPROC_MON and NSMPROC_UNMON upcalls
is a string that contains the hostname or IP address of the remote peer
to be notified when this host has rebooted.  The sm-notify command uses
this identifier to contact the peer when we reboot, so it must be
either a well-qualified DNS hostname or a presentation format IP
address string.

When the "nsm_use_hostnames" sysctl is set to zero, the kernel's NSM
provides a presentation format IP address in the "mon_name" argument.
Otherwise, the "caller_name" argument from NLM requests is used,
which is usually just the DNS hostname of the peer.

To support IPv6 addresses for the mon_name argument, we use the
nsm_handle's address eye-catcher, which already contains an appropriate
presentation format address string.  Using the eye-catcher string
obviates the need to use a large buffer on the stack to form the
presentation address string for the upcall.

This patch also addresses a subtle bug.

An NSMPROC_MON request and the subsequent NSMPROC_UNMON request for the
same peer are required to use the same value for the "mon_name"
argument.  Otherwise, rpc.statd's NSMPROC_UNMON processing cannot
locate the database entry for that peer and remove it.

If the setting of nsm_use_hostnames is changed between the time the
kernel sends an NSMPROC_MON request and the time it sends the
NSMPROC_UNMON request for the same peer, the "mon_name" argument for
these two requests may not be the same.  This is because the value of
"mon_name" is currently chosen at the moment the call is made based on
the setting of nsm_use_hostnames

To ensure both requests pass identical contents in the "mon_name"
argument, we now select which string to use for the argument in the
nsm_monitor() function.  A pointer to this string is saved in the
nsm_handle so it can be used for a subsequent NSMPROC_UNMON upcall.

NB: There are other potential problems, such as how nlm_host_rebooted()
might behave if nsm_use_hostnames were changed while hosts are still
being monitored.  This patch does not attempt to address those
problems.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

fs/lockd/mon.c

@@ -18,8 +18,6 @@
 
 #define NLMDBG_FACILITY		NLMDBG_MONITOR
 
-#define XDR_ADDRBUF_LEN		(20)
-
 static struct rpc_clnt *	nsm_create(void);
 
 static struct rpc_program	nsm_program;
@@ -42,7 +40,7 @@ nsm_mon_unmon(struct nsm_handle *nsm, u32 proc, struct nsm_res *res)
 		.prog		= NLM_PROGRAM,
 		.vers		= 3,
 		.proc		= NLMPROC_NSM_NOTIFY,
-		.mon_name	= nsm->sm_name,
+		.mon_name	= nsm->sm_mon_name,
 	};
 	struct rpc_message msg = {
 		.rpc_argp	= &args,
@@ -87,6 +85,12 @@ nsm_monitor(struct nlm_host *host)
 	if (nsm->sm_monitored)
 		return 0;
 
+	/*
+	 * Choose whether to record the caller_name or IP address of
+	 * this peer in the local rpc.statd's database.
+	 */
+	nsm->sm_mon_name = nsm_use_hostnames ? nsm->sm_name : nsm->sm_addrbuf;
+
 	status = nsm_mon_unmon(nsm, SM_MON, &res);
 
 	if (status < 0 || res.status != 0)
@@ -167,25 +171,10 @@ static __be32 *xdr_encode_nsm_string(__be32 *p, char *string)
 
 /*
  * "mon_name" specifies the host to be monitored.
- *
- * Linux uses a text version of the IP address of the remote
- * host as the host identifier (the "mon_name" argument).
- *
- * Linux statd always looks up the canonical hostname first for
- * whatever remote hostname it receives, so this works alright.
  */
 static __be32 *xdr_encode_mon_name(__be32 *p, struct nsm_args *argp)
 {
-	char	buffer[XDR_ADDRBUF_LEN + 1];
-	char	*name = argp->mon_name;
-
-	if (!nsm_use_hostnames) {
-		snprintf(buffer, XDR_ADDRBUF_LEN,
-			 "%pI4", &argp->addr);
-		name = buffer;
-	}
-
-	return xdr_encode_nsm_string(p, name);
+	return xdr_encode_nsm_string(p, argp->mon_name);
 }
 
 /*

include/linux/lockd/lockd.h

@@ -79,6 +79,7 @@ struct nlm_host {
 struct nsm_handle {
 	struct list_head	sm_link;
 	atomic_t		sm_count;
+	char			*sm_mon_name;
 	char			*sm_name;
 	struct sockaddr_storage	sm_addr;
 	size_t			sm_addrlen;