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From:   NeilBrown <neilb@suse.de>
To:     Steve Dickson <SteveD@RedHat.com>
Date:   Thu, 25 Feb 2021 13:42:47 +1100
Subject: [PATCH 5/5] mountd: make default ttl settable by option
Cc:     Linux NFS Mailing list <linux-nfs@vger.kernel.org>
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From: NeilBrown <neil@brown.name>

The DEFAULT_TTL affects the rate at which authentication messages are
logged.  So it is useful to make it settable.

Add "-ttl" and "-T", and add clear statement in the documentation of
both the benefits and the possible negative effects of choosing a larger
value

Signed-off-by: NeilBrown <neil@brown.name>
---
 support/export/cache.c     |    6 +++---
 support/export/v4root.c    |    3 ++-
 support/include/exportfs.h |    3 ++-
 support/nfs/exports.c      |    4 +++-
 utils/mountd/mountd.c      |   18 +++++++++++++++++-
 utils/mountd/mountd.man    |   19 ++++++++++++++++---
 6 files changed, 43 insertions(+), 10 deletions(-)

diff --git a/support/export/cache.c b/support/export/cache.c
index 50f7c7a15ceb..c0848c3e437b 100644
--- a/support/export/cache.c
+++ b/support/export/cache.c
@@ -157,7 +157,7 @@ static void auth_unix_ip(int f)
 	bp = buf; blen = sizeof(buf);
 	qword_add(&bp, &blen, "nfsd");
 	qword_add(&bp, &blen, ipaddr);
-	qword_adduint(&bp, &blen, time(0) + DEFAULT_TTL);
+	qword_adduint(&bp, &blen, time(0) + default_ttl);
 	if (use_ipaddr && client) {
 		memmove(ipaddr + 1, ipaddr, strlen(ipaddr) + 1);
 		ipaddr[0] = '$';
@@ -230,7 +230,7 @@ static void auth_unix_gid(int f)
 
 	bp = buf; blen = sizeof(buf);
 	qword_adduint(&bp, &blen, uid);
-	qword_adduint(&bp, &blen, time(0) + DEFAULT_TTL);
+	qword_adduint(&bp, &blen, time(0) + default_ttl);
 	if (rv >= 0) {
 		qword_adduint(&bp, &blen, ngroups);
 		for (i=0; i<ngroups; i++)
@@ -968,7 +968,7 @@ static int dump_to_cache(int f, char *buf, int blen, char *domain,
 	ssize_t err;
 
 	if (ttl <= 1)
-		ttl = DEFAULT_TTL;
+		ttl = default_ttl;
 
 	qword_add(&bp, &blen, domain);
 	qword_add(&bp, &blen, path);
diff --git a/support/export/v4root.c b/support/export/v4root.c
index 6f640aa9aa3f..3654bd7c10c0 100644
--- a/support/export/v4root.c
+++ b/support/export/v4root.c
@@ -45,7 +45,7 @@ static nfs_export pseudo_root = {
 		.e_nsqgids = 0,
 		.e_fsid = 0,
 		.e_mountpoint = NULL,
-		.e_ttl = DEFAULT_TTL,
+		.e_ttl = 0,
 	},
 	.m_exported = 0,
 	.m_xtabent = 1,
@@ -84,6 +84,7 @@ v4root_create(char *path, nfs_export *export)
 	struct exportent *curexp = &export->m_export;
 
 	dupexportent(&eep, &pseudo_root.m_export);
+	eep.e_ttl = default_ttl;
 	eep.e_hostname = curexp->e_hostname;
 	strncpy(eep.e_path, path, sizeof(eep.e_path)-1);
 	if (strcmp(path, "/") != 0)
diff --git a/support/include/exportfs.h b/support/include/exportfs.h
index daa7e2a06d82..81d137210862 100644
--- a/support/include/exportfs.h
+++ b/support/include/exportfs.h
@@ -105,7 +105,8 @@ typedef struct mexport {
 } nfs_export;
 
 #define HASH_TABLE_SIZE 1021
-#define DEFAULT_TTL	(30 * 60)
+
+extern int default_ttl;
 
 typedef struct _exp_hash_entry {
 	nfs_export * p_first;
diff --git a/support/nfs/exports.c b/support/nfs/exports.c
index 037febd08d9b..2c8f0752ad9d 100644
--- a/support/nfs/exports.c
+++ b/support/nfs/exports.c
@@ -47,6 +47,8 @@ struct flav_info flav_map[] = {
 
 const int flav_map_size = sizeof(flav_map)/sizeof(flav_map[0]);
 
+int default_ttl = 30 * 60;
+
 static char	*efname = NULL;
 static XFILE	*efp = NULL;
 static int	first;
@@ -100,7 +102,7 @@ static void init_exportent (struct exportent *ee, int fromkernel)
 	ee->e_nsquids = 0;
 	ee->e_nsqgids = 0;
 	ee->e_uuid = NULL;
-	ee->e_ttl = DEFAULT_TTL;
+	ee->e_ttl = default_ttl;
 }
 
 struct exportent *
diff --git a/utils/mountd/mountd.c b/utils/mountd/mountd.c
index dafcc35ca9c2..22279e9afe48 100644
--- a/utils/mountd/mountd.c
+++ b/utils/mountd/mountd.c
@@ -76,9 +76,10 @@ static struct option longopts[] =
 	{ "no-udp", 0, 0, 'u' },
 	{ "log-auth", 0, 0, 'l'},
 	{ "cache-use-ipaddr", 0, 0, 'i'},
+	{ "ttl", 1, 0, 'T'},
 	{ NULL, 0, 0, 0 }
 };
-static char shortopts[] = "o:nFd:p:P:hH:N:V:vurs:t:gli";
+static char shortopts[] = "o:nFd:p:P:hH:N:V:vurs:t:gliT";
 
 #define NFSVERSBIT(vers)	(0x1 << (vers - 1))
 #define NFSVERSBIT_ALL		(NFSVERSBIT(2) | NFSVERSBIT(3) | NFSVERSBIT(4))
@@ -672,6 +673,7 @@ inline static void
 read_mountd_conf(char **argv)
 {
 	char	*s;
+	int	ttl;
 
 	conf_init_file(NFS_CONFFILE);
 
@@ -706,6 +708,10 @@ read_mountd_conf(char **argv)
 		else
 			NFSCTL_VERUNSET(nfs_version, vers);
 	}
+
+	ttl = conf_get_num("mountd", "ttl", default_ttl);
+	if (ttl > 0)
+		default_ttl = ttl;
 }
 
 int
@@ -715,6 +721,7 @@ main(int argc, char **argv)
 	unsigned int listeners = 0;
 	int	foreground = 0;
 	int	c;
+	int	ttl;
 	struct sigaction sa;
 	struct rlimit rlim;
 
@@ -809,6 +816,15 @@ main(int argc, char **argv)
 		case 'i':
 			use_ipaddr = 2;
 			break;
+		case 'T':
+			ttl = atoi(optarg);
+			if (ttl <= 0) {
+				fprintf(stderr, "%s: bad ttl number of seconds: %s\n",
+					argv[0], optarg);
+				usage(argv[0], 1);
+			}
+			default_ttl = ttl;
+			break;
 		case 0:
 			break;
 		case '?':
diff --git a/utils/mountd/mountd.man b/utils/mountd/mountd.man
index 44d237e56110..82e07cf221fa 100644
--- a/utils/mountd/mountd.man
+++ b/utils/mountd/mountd.man
@@ -99,9 +99,10 @@ Turn on debugging. Valid kinds are: all, auth, call, general and parse.
 .TP
 .BR \-l " or " \-\-log\-auth
 Enable logging of responses to authentication and access requests from
-nfsd.  Each response is then cached by the kernel for 30 minutes, and
-will be refreshed after 15 minutes if the relevant client remains
-active.
+nfsd.  Each response is then cached by the kernel for 30 minutes (or as set by
+.B \-\-ttl
+below), and will be refreshed after 15 minutes (half the ttl time) if
+the relevant client remains active.
 Note that
 .B -l
 is equivalent to
@@ -135,6 +136,17 @@ log messages produced by the
 .B -l
 option easier to read.
 .TP
+.B \-T " or " \-\-ttl
+Provide a time-to-live (TTL) for cached information given to the kernel.
+The kernel will normally request an update if the information is needed
+after half of this time has expired.  Increasing the provided number,
+which is in seconds, reduces the rate of cache update requests, and this
+is particularly noticeable when these requests are logged with
+.BR \-l .
+However increasing also means that changes to hostname to address
+mappings can take longer to be noticed.
+The default TTL is 1800 (30 minutes).
+.TP
 .B \-F " or " \-\-foreground
 Run in foreground (do not daemonize)
 .TP
@@ -269,6 +281,7 @@ section include
 .BR descriptors ,
 .BR port ,
 .BR threads ,
+.BR ttl ,
 .BR reverse-lookup ", and"
 .BR state-directory-path ,
 .B ha-callout