primitives for maintaining persisitency

* d_make_persistent(dentry, inode) - bump refcount, mark persistent and
make hashed positive.  Return value is a borrowed reference to dentry;
it can be used until something removes persistency (at the very least,
until the parent gets unlocked, but some filesystems may have stronger
exclusion).

* d_make_discardable() - remove persistency mark and drop reference.

d_make_persistent() is similar to combination of d_instantiate(), dget()
and setting flag.  The only difference is that unlike d_instantiate()
it accepts hashed and unhashed negatives alike.  It is always called in
strong locking environment (parent held exclusive, or, in some cases,
dentry coming from d_alloc_name()); if we ever start using it with parent
held only shared and dentry coming from d_alloc_parallel(), we'll need
to copy the in-lookup logics from __d_add().

d_make_discardable() is eqiuvalent to combination of removing flag and
dput(); since flag removal requires ->d_lock, there's no point trying
to avoid taking that for refcount decrement as fast_dput() does.
The slow path of dput() has been taken into a helper and reused in
d_make_discardable() instead.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 94b58655322a..6ec4066825e3 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -611,5 +611,7 @@ static inline struct dentry *d_next_sibling(const struct dentry *dentry)
 }
 
 void set_default_d_op(struct super_block *, const struct dentry_operations *);
+struct dentry *d_make_persistent(struct dentry *, struct inode *);
+void d_make_discardable(struct dentry *dentry);
 
 #endif	/* __LINUX_DCACHE_H */