nfs-utils: have mountd hold open etab file to force inode number to change

This patch changes mountd to hold the etab file open so that when it's
changed by exportfs, the inode number should change. We then change
auth_reload to reload the file based on whether st_ino is different
from the last time it was checked. It also changes auth_reload to
maintain a static counter value and return it instead of a timestamp
and fixes up get_exportlist accordingly. Finally, it adds some
comments to xtab_write to warn people about editing the etab in place.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 20 insertions, 9 deletions

diff --git a/utils/mountd/auth.c b/utils/mountd/auth.c
index 183c9ea..f7fe23d 100644
--- a/utils/mountd/auth.c
+++ b/utils/mountd/auth.c
@@ -14,6 +14,7 @@
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <errno.h>
+#include <unistd.h>
 #include "misc.h"
 #include "nfslib.h"
 #include "exportfs.h"
@@ -46,24 +47,34 @@ auth_init(char *exports)
 	xtab_mount_write();
 }
 
-time_t
+unsigned int
 auth_reload()
 {
 	struct stat		stb;
-	static time_t		last_modified = 0;
-
-	if (stat(_PATH_ETAB, &stb) < 0)
+	static ino_t		last_inode;
+	static int		last_fd;
+	static unsigned int	counter;
+	int			fd;
+
+	if ((fd = open(_PATH_ETAB, O_RDONLY)) < 0) {
+		xlog(L_FATAL, "couldn't open %s", _PATH_ETAB);
+	} else if (fstat(fd, &stb) < 0) {
 		xlog(L_FATAL, "couldn't stat %s", _PATH_ETAB);
-	if (stb.st_mtime == last_modified)
-		return last_modified;
-	last_modified = stb.st_mtime;
+	} else if (stb.st_ino == last_inode) {
+		close(fd);
+		return counter;
+	} else {
+		close(last_fd);
+		last_fd = fd;
+		last_inode = stb.st_ino;
+	}
 
 	export_freeall();
 	memset(&my_client, 0, sizeof(my_client));
-	// export_read(export_file);
 	xtab_export_read();
+	++counter;
 
-	return last_modified;
+	return counter;
 }
 
 static nfs_export *