fs/namei.c: pull positivity check into follow_managed()

There are 4 callers; two proceed to check if result is positive and
fail with ENOENT if it isn't; one (in handle_lookup_down()) is
guaranteed to yield positive and one (in lookup_fast()) is _preceded_
by positivity check.

However, follow_managed() on a negative dentry is a (fairly cheap)
no-op on anything other than autofs.  And negative autofs dentries
are never hashed, so lookup_fast() is not going to run into one
of those.  Moreover, successful follow_managed() on a _positive_
dentry never yields a negative one (and we significantly rely upon
that in callers of lookup_fast()).

In other words, we can easily transpose the positivity check and
the call of follow_managed() in lookup_fast().  And that allows
to fold the positivity check *into* follow_managed(), simplifying
life for the code downstream of its calls.

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

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 10090f11ab95..c1488cc84fd9 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -440,6 +440,11 @@ static inline bool d_is_negative(const struct dentry *dentry)
 	return d_is_miss(dentry);
 }
 
+static inline bool d_flags_negative(unsigned flags)
+{
+	return (flags & DCACHE_ENTRY_TYPE) == DCACHE_MISS_TYPE;
+}
+
 static inline bool d_is_positive(const struct dentry *dentry)
 {
 	return !d_is_negative(dentry);