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, 1 insertions, 0 deletions

diff --git a/fs/autofs/autofs_i.h b/fs/autofs/autofs_i.h
index 9b81c10ef251..3e59f0ed777b 100644
--- a/fs/autofs/autofs_i.h
+++ b/fs/autofs/autofs_i.h
@@ -104,6 +104,7 @@ struct autofs_wait_queue {
 #define AUTOFS_SBI_MAGIC 0x6d4a556d
 
 #define AUTOFS_SBI_CATATONIC	0x0001
+#define AUTOFS_SBI_STRICTEXPIRE 0x0002
 
 struct autofs_sb_info {
 	u32 magic;