[PATCH 6/8] mountd: don't add paths to non-mounted export points to pseudo-root

[NeilBrown <neilb@suse.com>]

export points with the "mountpoint" flag should not be exported
if they aren't mounted.
They shouldn't even appear in the pseudo-root filesystem.
So add an appropriate check to v4root_set().

This means that the v4root might need to be recomputed whenever a
filesystem is mounted or unmounted.  So when there are export points
with the "mountpoint" flag, check for changes in the mount table.
This is done be measuring the size of /proc/mounts.

Signed-off-by: NeilBrown <neilb@suse.com>
---
 support/include/v4root.h |    2 +-
 utils/mountd/auth.c      |   29 +++++++++++++++++++++++++++--
 utils/mountd/v4root.c    |   11 ++++++++++-
 3 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/support/include/v4root.h b/support/include/v4root.h
index 706c15c70d95..406fd4e43e5a 100644
--- a/support/include/v4root.h
+++ b/support/include/v4root.h
@@ -10,6 +10,6 @@
 #define V4ROOT_H
 
 extern int v4root_needed;
-extern void v4root_set(void);
+extern void v4root_set(int *mountpoints_checked);
 
 #endif /* V4ROOT_H */
diff --git a/utils/mountd/auth.c b/utils/mountd/auth.c
index 0881d9a6edba..5bd7e6622307 100644
--- a/utils/mountd/auth.c
+++ b/utils/mountd/auth.c
@@ -77,6 +77,29 @@ check_useipaddr(void)
 		cache_flush(1);
 }
 
+static int mountpoints_changed(void)
+{
+	static int last_size = 0;
+	int size;
+	int fd;
+	char buf[4096];
+	int n;
+
+	fd = open("/proc/mounts", O_RDONLY);
+	if (fd < 0)
+		/* ignore mountpoint changes if we cannot read /proc/mounts */
+		return 0;
+	size = 0;
+	while ((n = read(fd, buf, sizeof(buf))) > 0)
+		size += n;
+	if (n < 0)
+		return 0;
+	if (size == last_size)
+		return 0;
+	last_size = size;
+	return 1;
+}
+
 unsigned int
 auth_reload()
 {
@@ -84,6 +107,7 @@ auth_reload()
 	static ino_t		last_inode;
 	static int		last_fd = -1;
 	static unsigned int	counter;
+	static int		mountpoints_checked = 0;
 	int			fd;
 
 	if ((fd = open(_PATH_ETAB, O_RDONLY)) < 0) {
@@ -91,7 +115,8 @@ auth_reload()
 	} else if (fstat(fd, &stb) < 0) {
 		xlog(L_FATAL, "couldn't stat %s", _PATH_ETAB);
 		close(fd);
-	} else if (last_fd != -1 && stb.st_ino == last_inode) {
+	} else if (last_fd != -1 && stb.st_ino == last_inode &&
+		   (!mountpoints_checked || !mountpoints_changed())) {
 		/* We opened the etab file before, and its inode
 		 * number hasn't changed since then.
 		 */
@@ -114,7 +139,7 @@ auth_reload()
 	memset(&my_client, 0, sizeof(my_client));
 	xtab_export_read();
 	check_useipaddr();
-	v4root_set();
+	v4root_set(&mountpoints_checked);
 
 	++counter;
 
diff --git a/utils/mountd/v4root.c b/utils/mountd/v4root.c
index d52172592823..1a5778f9c7de 100644
--- a/utils/mountd/v4root.c
+++ b/utils/mountd/v4root.c
@@ -183,7 +183,7 @@ static int v4root_add_parents(nfs_export *exp)
  * looking for components of the v4 mount.
  */
 void
-v4root_set()
+v4root_set(int *mountpoints_checked)
 {
 	nfs_export	*exp;
 	int	i;
@@ -193,6 +193,7 @@ v4root_set()
 	if (!v4root_support())
 		return;
 
+	*mountpoints_checked = 0;
 	for (i = 0; i < MCL_MAXTYPES; i++) {
 		for (exp = exportlist[i].p_head; exp; exp = exp->m_next) {
 			if (exp->m_export.e_flags & NFSEXP_V4ROOT)
@@ -202,6 +203,14 @@ v4root_set()
 				 */
 				continue;
 
+			if (exp->m_export.e_mountpoint) {
+				*mountpoints_checked = 1;
+				if (!is_mountpoint(exp->m_export.e_mountpoint[0]?
+						   exp->m_export.e_mountpoint:
+						   exp->m_export.e_path))
+					continue;
+			}
+
 			if (strcmp(exp->m_export.e_path, "/") == 0 &&
 			    !(exp->m_export.e_flags & NFSEXP_FSID)) {
 				/* Force '/' to be exported as fsid == 0*/