From 87335787bab64d78059c248ce95c16b88a512dfb Mon Sep 17 00:00:00 2001
From: George Wilson <gwilson@zfsmail.com>
Date: Mon, 8 Apr 2019 21:37:50 -0600
Subject: [PATCH] DLPX-62600 zfs sharenfs commands make slow progress on
 scalability system (#45)

Signed-off-by: Bryant G. Ly <bly@catalogicsoftware.com>

Conflicts:
	cmd/zpool/zpool_main.c
---
 cmd/zpool/zpool_main.c        |  5 ++---
 lib/libshare/libshare.c       | 20 ++++++++++++++++++++
 lib/libspl/include/libshare.h |  1 +
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/cmd/zpool/zpool_main.c b/cmd/zpool/zpool_main.c
index 1e4cfaefab74..745837d0d183 100644
--- a/cmd/zpool/zpool_main.c
+++ b/cmd/zpool/zpool_main.c
@@ -1648,12 +1648,9 @@ zpool_export_one(zpool_handle_t *zhp, void *data)
 {
 	export_cbdata_t *cb = data;
 
-	verify(sharetab_lock() == 0);
 	if (zpool_disable_datasets(zhp, cb->force || cb->hardforce) != 0) {
-		verify(sharetab_unlock() == 0);
 		return (1);
 	}
-	verify(sharetab_unlock() == 0);
 
 	/* The history must be logged as part of the export */
 	log_history = B_FALSE;
@@ -1727,7 +1724,9 @@ zpool_do_export(int argc, char **argv)
 		usage(B_FALSE);
 	}
 
+	verify(sharetab_lock() == 0);
 	ret = for_each_pool(argc, argv, B_TRUE, NULL, zpool_export_one, &cb);
+	verify(sharetab_unlock() == 0);
 
 	return (ret);
 }
diff --git a/lib/libshare/libshare.c b/lib/libshare/libshare.c
index a315e6deeabb..0b4de53e53be 100644
--- a/lib/libshare/libshare.c
+++ b/lib/libshare/libshare.c
@@ -92,6 +92,20 @@ sa_init(int init_service)
 
 	impl_handle->zfs_libhandle = libzfs_init();
 
+	/*
+	 * When libshare initializes the shares below, it needs to parse the
+	 * MNTTAB to determine if a filesystem is mounted by calling
+	 * zfs_is_mounted(). On systems with thousands of filesystems,
+	 * repeatedly parsing the MNTTAB can be very slow. As a performance
+	 * improvement, we cache the MNTTAB so that we only have to read it
+	 * once. Repeated calls to zfs_is_mounted will just lookup entries in
+	 * the AVL tree. We can only safely do this when we've locked the
+	 * sharetab to other zfs sharenfs operations from concurrently
+	 * updating the MNTTAB.
+	 */
+	if (sharetab_locked())
+		libzfs_mnttab_cache(impl_handle->zfs_libhandle, B_TRUE);
+
 	if (impl_handle->zfs_libhandle != NULL) {
 		libzfs_print_on_error(impl_handle->zfs_libhandle, B_TRUE);
 	}
@@ -218,6 +232,12 @@ sharetab_unlock(void)
 	return (retval);
 }
 
+boolean_t
+sharetab_locked(void)
+{
+	return(sharetab_fd != -1);
+}
+
 static void
 update_sharetab(sa_handle_impl_t impl_handle)
 {
diff --git a/lib/libspl/include/libshare.h b/lib/libspl/include/libshare.h
index 4831d2260abb..acd9f4dc9810 100644
--- a/lib/libspl/include/libshare.h
+++ b/lib/libspl/include/libshare.h
@@ -87,6 +87,7 @@ extern int sa_generate_share(const char *, const char *);
 
 extern int sharetab_lock(void);
 extern int sharetab_unlock(void);
+extern boolean_t sharetab_locked(void);
 
 /* protocol specific interfaces */
 extern int sa_parse_legacy_options(sa_group_t, char *, char *);