autofs4: Add d_manage() dentry operation

This patch required a previous patch to add the ->d_automount()
dentry operation.

Add a function to use the newly defined ->d_manage() dentry operation
for blocking during mount and expire.

Whether the VFS calls the dentry operations d_automount() and d_manage()
is controled by the DMANAGED_AUTOMOUNT and DMANAGED_TRANSIT flags. autofs
uses the d_automount() operation to callback to user space to request
mount operations and the d_manage() operation to block walks into mounts
that are under construction or destruction.

In order to prevent these functions from being called unnecessarily the
DMANAGED_* flags are cleared for cases which would cause this. In the
common case the DMANAGED_AUTOMOUNT and DMANAGED_TRANSIT flags are both
set for dentrys waiting to be mounted. The DMANAGED_TRANSIT flag is
cleared upon successful mount request completion and set during expire
runs, both during the dentry expire check, and if selected for expire,
is left set until a subsequent successful mount request completes.

The exception to this is the so-called rootless multi-mount which has
no actual mount at its base. In this case the DMANAGED_AUTOMOUNT flag
is cleared upon successful mount request completion as well and set
again after a successful expire.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c
index d0aa38cac302..75c1ed8e2fb9 100644
--- a/fs/autofs4/inode.c
+++ b/fs/autofs4/inode.c
@@ -253,6 +253,7 @@ static struct autofs_info *autofs4_mkroot(struct autofs_sb_info *sbi)
 
 static const struct dentry_operations autofs4_sb_dentry_operations = {
         .d_automount    = autofs4_d_automount,
+        .d_manage       = autofs4_d_manage,
         .d_release      = autofs4_dentry_release,
 };
 
@@ -322,7 +323,7 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
         }
 
         if (autofs_type_trigger(sbi->type))
-                __managed_dentry_set_automount(root);
+                __managed_dentry_set_managed(root);
 
         root_inode->i_fop = &autofs4_root_operations;
         root_inode->i_op = autofs_type_trigger(sbi->type) ?