autofs: add strictexpire mount option

Commit 092a53452bb7 ("autofs: take more care to not update last_used on
path walk") helped to (partially) resolve a problem where automounts
were not expiring due to aggressive accesses from user space.

This patch was later reverted because, for very large environments, it
meant more mount requests from clients and when there are a lot of
clients this caused a fairly significant increase in server load.

But there is a need for both types of expire check, depending on use
case, so add a mount option to allow for strict update of last use of
autofs dentrys (which just means not updating the last use on path walk
access).

Link: http://lkml.kernel.org/r/154296973880.9889.14085372741514507967.stgit@pluto-themaw-net
Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/fs/autofs/inode.c b/fs/autofs/inode.c
index 3a94dbda36dd..0e8ea2d9a2bb 100644
--- a/fs/autofs/inode.c
+++ b/fs/autofs/inode.c
@@ -87,6 +87,8 @@ static int autofs_show_options(struct seq_file *m, struct dentry *root)
 		seq_printf(m, ",direct");
 	else
 		seq_printf(m, ",indirect");
+	if (sbi->flags & AUTOFS_SBI_STRICTEXPIRE)
+		seq_printf(m, ",strictexpire");
 #ifdef CONFIG_CHECKPOINT_RESTORE
 	if (sbi->pipe)
 		seq_printf(m, ",pipe_ino=%ld", file_inode(sbi->pipe)->i_ino);
@@ -109,7 +111,7 @@ static const struct super_operations autofs_sops = {
 };
 
 enum {Opt_err, Opt_fd, Opt_uid, Opt_gid, Opt_pgrp, Opt_minproto, Opt_maxproto,
-	Opt_indirect, Opt_direct, Opt_offset};
+	Opt_indirect, Opt_direct, Opt_offset, Opt_strictexpire};
 
 static const match_table_t tokens = {
 	{Opt_fd, "fd=%u"},
@@ -121,6 +123,7 @@ static const match_table_t tokens = {
 	{Opt_indirect, "indirect"},
 	{Opt_direct, "direct"},
 	{Opt_offset, "offset"},
+	{Opt_strictexpire, "strictexpire"},
 	{Opt_err, NULL}
 };
 
@@ -200,6 +203,9 @@ static int parse_options(char *options,
 		case Opt_offset:
 			set_autofs_type_offset(&sbi->type);
 			break;
+		case Opt_strictexpire:
+			sbi->flags |= AUTOFS_SBI_STRICTEXPIRE;
+			break;
 		default:
 			return 1;
 		}