[PATCH 3/4] dcache: Don't set DISCONNECTED on "pseudo filesystem" dentries

["J. Bruce Fields" <bfields@redhat.com>]

From: "J. Bruce Fields" <bfields@redhat.com>

I can't for the life of me see any reason why anyone should care whether
a dentry that is never hooked into the dentry cache would need
DCACHE_DISCONNECTED set.

This originates from 4b936885ab04dc6e0bb0ef35e0e23c1a7364d9e5 "fs:
improve scalability of pseudo filesystems", which probably just made the
false assumption the DCACHE_DISCONNECTED was meant to be set on anything
not connected to a parent somehow.

So this is just confusing.  Ideally the only uses of DCACHE_DISCONNECTED
would be in the filehandle-lookup code, which needs it to ensure
dentries are connected into the dentry tree before use.

I left d_alloc_pseudo there even though it's now equivalent to
__d_alloc(), just on the theory the name is better documentation of its
intended use outside dcache.c.

Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/dcache.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index d9e4fba..a53f55d 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1312,12 +1312,17 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
 }
 EXPORT_SYMBOL(d_alloc);
 
+/**
+ * d_alloc_pseudo - allocate a dentry (for lookup-less filesystems)
+ * @sb: the superblock
+ * @name: qstr of the name
+ *
+ * For a filesystem that just pins its dentries in memory and never
+ * performs lookups at all, return an unhashed IS_ROOT dentry.
+ */
 struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
 {
-	struct dentry *dentry = __d_alloc(sb, name);
-	if (dentry)
-		dentry->d_flags |= DCACHE_DISCONNECTED;
-	return dentry;
+	return __d_alloc(sb, name);
 }
 EXPORT_SYMBOL(d_alloc_pseudo);
 
-- 
1.7.9.5