From 12f8ad4b0533d9212cb1d5e58ed73d2170114785 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 4 May 2012 14:59:14 -0700
Subject: vfs: clean up __d_lookup_rcu() and dentry_cmp() interfaces

The calling conventions for __d_lookup_rcu() and dentry_cmp() are
annoying in different ways, and there is actually one single underlying
reason for both of the annoyances.

The fundamental reason is that we do the returned dentry sequence number
check inside __d_lookup_rcu() instead of doing it in the caller.  This
results in two annoyances:

 - __d_lookup_rcu() now not only needs to return the dentry and the
   sequence number that goes along with the lookup, it also needs to
   return the inode pointer that was validated by that sequence number
   check.

 - and because we did the sequence number check early (to validate the
   name pointer and length) we also couldn't just pass the dentry itself
   to dentry_cmp(), we had to pass the counted string that contained the
   name.

So that sequence number decision caused two separate ugly calling
conventions.

Both of these problems would be solved if we just did the sequence
number check in the caller instead.  There's only one caller, and that
caller already has to do the sequence number check for the parent
anyway, so just do that.

That allows us to stop returning the dentry->d_inode in that in-out
argument (pointer-to-pointer-to-inode), so we can make the inode
argument just a regular input inode pointer.  The caller can just load
the inode from dentry->d_inode, and then do the sequence number check
after that to make sure that it's synchronized with the name we looked
up.

And it allows us to just pass in the dentry to dentry_cmp(), which is
what all the callers really wanted.  Sure, dentry_cmp() has to be a bit
careful about the dentry (which is not stable during RCU lookup), but
that's actually very simple.

And now that dentry_cmp() can clearly see that the first string argument
is a dentry, we can use the direct word access for that, instead of the
careful unaligned zero-padding.  The dentry name is always properly
aligned, since it is a single path component that is either embedded
into the dentry itself, or was allocated with kmalloc() (see __d_alloc).

Finally, this also uninlines the nasty slow-case for dentry comparisons:
that one *does* need to do a sequence number check, since it will call
in to the low-level filesystems, and we want to give those a stable
inode pointer and path component length/start arguments.  Doing an extra
sequence check for that slow case is not a problem, though.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/dcache.c b/fs/dcache.c
index b80531c..539943e 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -153,16 +153,33 @@ int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,
  * In contrast, 'ct' and 'tcount' can be from a pathname, and do
  * need the careful unaligned handling.
  */
-static inline int dentry_cmp(const unsigned char *cs, size_t scount,
-				const unsigned char *ct, size_t tcount)
+static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
 {
 	unsigned long a,b,mask;
+	const unsigned char *cs;
 
-	if (unlikely(scount != tcount))
+	if (unlikely(dentry->d_name.len != tcount))
 		return 1;
+	/*
+	 * Be careful about RCU walk racing with rename:
+	 * use ACCESS_ONCE to fetch the name pointer.
+	 *
+	 * NOTE! Even if a rename will mean that the length
+	 * was not loaded atomically, we don't care. The
+	 * RCU walk will check the sequence count eventually,
+	 * and catch it. And we won't overrun the buffer,
+	 * because we're reading the name pointer atomically,
+	 * and a dentry name is guaranteed to be properly
+	 * terminated with a NUL byte.
+	 *
+	 * End result: even if 'len' is wrong, we'll exit
+	 * early because the data cannot match (there can
+	 * be no NUL in the ct/tcount data)
+	 */
+	cs = ACCESS_ONCE(dentry->d_name.name);
 
 	for (;;) {
-		a = load_unaligned_zeropad(cs);
+		a = *(unsigned long *)cs;
 		b = load_unaligned_zeropad(ct);
 		if (tcount < sizeof(unsigned long))
 			break;
@@ -180,10 +197,11 @@ static inline int dentry_cmp(const unsigned char *cs, size_t scount,
 
 #else
 
-static inline int dentry_cmp(const unsigned char *cs, size_t scount,
-				const unsigned char *ct, size_t tcount)
+static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
 {
-	if (scount != tcount)
+	const unsigned char *cs = dentry->d_name.name;
+
+	if (dentry->d_name.len != tcount)
 		return 1;
 
 	do {
@@ -1439,18 +1457,16 @@ static struct dentry *__d_instantiate_unique(struct dentry *entry,
 	}
 
 	list_for_each_entry(alias, &inode->i_dentry, d_alias) {
-		struct qstr *qstr = &alias->d_name;
-
 		/*
 		 * Don't need alias->d_lock here, because aliases with
 		 * d_parent == entry->d_parent are not subject to name or
 		 * parent changes, because the parent inode i_mutex is held.
 		 */
-		if (qstr->hash != hash)
+		if (alias->d_name.hash != hash)
 			continue;
 		if (alias->d_parent != entry->d_parent)
 			continue;
-		if (dentry_cmp(qstr->name, qstr->len, name, len))
+		if (dentry_cmp(alias, name, len))
 			continue;
 		__dget(alias);
 		return alias;
@@ -1727,6 +1743,48 @@ err_out:
 }
 EXPORT_SYMBOL(d_add_ci);
 
+/*
+ * Do the slow-case of the dentry name compare.
+ *
+ * Unlike the dentry_cmp() function, we need to atomically
+ * load the name, length and inode information, so that the
+ * filesystem can rely on them, and can use the 'name' and
+ * 'len' information without worrying about walking off the
+ * end of memory etc.
+ *
+ * Thus the read_seqcount_retry() and the "duplicate" info
+ * in arguments (the low-level filesystem should not look
+ * at the dentry inode or name contents directly, since
+ * rename can change them while we're in RCU mode).
+ */
+enum slow_d_compare {
+	D_COMP_OK,
+	D_COMP_NOMATCH,
+	D_COMP_SEQRETRY,
+};
+
+static noinline enum slow_d_compare slow_dentry_cmp(
+		const struct dentry *parent,
+		struct inode *inode,
+		struct dentry *dentry,
+		unsigned int seq,
+		const struct qstr *name)
+{
+	int tlen = dentry->d_name.len;
+	const char *tname = dentry->d_name.name;
+	struct inode *i = dentry->d_inode;
+
+	if (read_seqcount_retry(&dentry->d_seq, seq)) {
+		cpu_relax();
+		return D_COMP_SEQRETRY;
+	}
+	if (parent->d_op->d_compare(parent, inode,
+				dentry, i,
+				tlen, tname, name))
+		return D_COMP_NOMATCH;
+	return D_COMP_OK;
+}
+
 /**
  * __d_lookup_rcu - search for a dentry (racy, store-free)
  * @parent: parent dentry
@@ -1753,10 +1811,13 @@ EXPORT_SYMBOL(d_add_ci);
  * the returned dentry, so long as its parent's seqlock is checked after the
  * child is looked up. Thus, an interlocking stepping of sequence lock checks
  * is formed, giving integrity down the path walk.
+ *
+ * NOTE! The caller *has* to check the resulting dentry against the sequence
+ * number we've returned before using any of the resulting dentry state!
  */
 struct dentry *__d_lookup_rcu(const struct dentry *parent,
 				const struct qstr *name,
-				unsigned *seqp, struct inode **inode)
+				unsigned *seqp, struct inode *inode)
 {
 	unsigned int len = name->len;
 	unsigned int hash = name->hash;
@@ -1787,49 +1848,46 @@ struct dentry *__d_lookup_rcu(const struct dentry *parent,
 	 */
 	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
 		unsigned seq;
-		struct inode *i;
-		const char *tname;
-		int tlen;
 
 		if (dentry->d_name.hash != hash)
 			continue;
 
 seqretry:
-		seq = read_seqcount_begin(&dentry->d_seq);
+		/*
+		 * The dentry sequence count protects us from concurrent
+		 * renames, and thus protects inode, parent and name fields.
+		 *
+		 * The caller must perform a seqcount check in order
+		 * to do anything useful with the returned dentry,
+		 * including using the 'd_inode' pointer.
+		 *
+		 * NOTE! We do a "raw" seqcount_begin here. That means that
+		 * we don't wait for the sequence count to stabilize if it
+		 * is in the middle of a sequence change. If we do the slow
+		 * dentry compare, we will do seqretries until it is stable,
+		 * and if we end up with a successful lookup, we actually
+		 * want to exit RCU lookup anyway.
+		 */
+		seq = raw_seqcount_begin(&dentry->d_seq);
 		if (dentry->d_parent != parent)
 			continue;
 		if (d_unhashed(dentry))
 			continue;
-		tlen = dentry->d_name.len;
-		tname = dentry->d_name.name;
-		i = dentry->d_inode;
-		prefetch(tname);
-		/*
-		 * This seqcount check is required to ensure name and
-		 * len are loaded atomically, so as not to walk off the
-		 * edge of memory when walking. If we could load this
-		 * atomically some other way, we could drop this check.
-		 */
-		if (read_seqcount_retry(&dentry->d_seq, seq))
-			goto seqretry;
+		*seqp = seq;
+
 		if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
-			if (parent->d_op->d_compare(parent, *inode,
-						dentry, i,
-						tlen, tname, name))
-				continue;
-		} else {
-			if (dentry_cmp(tname, tlen, str, len))
+			switch (slow_dentry_cmp(parent, inode, dentry, seq, name)) {
+			case D_COMP_OK:
+				return dentry;
+			case D_COMP_NOMATCH:
 				continue;
+			default:
+				goto seqretry;
+			}
 		}
-		/*
-		 * No extra seqcount check is required after the name
-		 * compare. The caller must perform a seqcount check in
-		 * order to do anything useful with the returned dentry
-		 * anyway.
-		 */
-		*seqp = seq;
-		*inode = i;
-		return dentry;
+
+		if (!dentry_cmp(dentry, str, len))
+			return dentry;
 	}
 	return NULL;
 }
@@ -1908,8 +1966,6 @@ struct dentry *__d_lookup(struct dentry *parent, struct qstr *name)
 	rcu_read_lock();
 	
 	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
-		const char *tname;
-		int tlen;
 
 		if (dentry->d_name.hash != hash)
 			continue;
@@ -1924,15 +1980,15 @@ struct dentry *__d_lookup(struct dentry *parent, struct qstr *name)
 		 * It is safe to compare names since d_move() cannot
 		 * change the qstr (protected by d_lock).
 		 */
-		tlen = dentry->d_name.len;
-		tname = dentry->d_name.name;
 		if (parent->d_flags & DCACHE_OP_COMPARE) {
+			int tlen = dentry->d_name.len;
+			const char *tname = dentry->d_name.name;
 			if (parent->d_op->d_compare(parent, parent->d_inode,
 						dentry, dentry->d_inode,
 						tlen, tname, name))
 				goto next;
 		} else {
-			if (dentry_cmp(tname, tlen, str, len))
+			if (dentry_cmp(dentry, str, len))
 				goto next;
 		}
 
diff --git a/fs/namei.c b/fs/namei.c
index c427919..46bd004 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1154,12 +1154,25 @@ static int do_lookup(struct nameidata *nd, struct qstr *name,
 	 */
 	if (nd->flags & LOOKUP_RCU) {
 		unsigned seq;
-		*inode = nd->inode;
-		dentry = __d_lookup_rcu(parent, name, &seq, inode);
+		dentry = __d_lookup_rcu(parent, name, &seq, nd->inode);
 		if (!dentry)
 			goto unlazy;
 
-		/* Memory barrier in read_seqcount_begin of child is enough */
+		/*
+		 * This sequence count validates that the inode matches
+		 * the dentry name information from lookup.
+		 */
+		*inode = dentry->d_inode;
+		if (read_seqcount_retry(&dentry->d_seq, seq))
+			return -ECHILD;
+
+		/*
+		 * This sequence count validates that the parent had no
+		 * changes while we did the lookup of the dentry above.
+		 *
+		 * The memory barrier in read_seqcount_begin of child is
+		 *  enough, we can use __read_seqcount_retry here.
+		 */
 		if (__read_seqcount_retry(&parent->d_seq, nd->seq))
 			return -ECHILD;
 		nd->seq = seq;
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 7e11f14..8239f64 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -282,7 +282,7 @@ extern struct dentry *d_hash_and_lookup(struct dentry *, struct qstr *);
 extern struct dentry *__d_lookup(struct dentry *, struct qstr *);
 extern struct dentry *__d_lookup_rcu(const struct dentry *parent,
 				const struct qstr *name,
-				unsigned *seq, struct inode **inode);
+				unsigned *seq, struct inode *inode);
 
 /**
  * __d_rcu_to_refcount - take a refcount on dentry if sequence check is ok
-- 
cgit v0.10.2


From 8c01a529b861ba97c7d78368e6a5d4d42e946f75 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 10 May 2012 11:06:18 -0700
Subject: vfs: remove unnecessary d_unhashed() check from __d_lookup_rcu

The check for d_unhashed() is not strictly incorrect, but at the same
time it is also not sensible.  The actual dentry removal from the dentry
hash chains is totally asynchronous to the __d_lookup_rcu() logic, and
we depend on __d_drop() updating the sequence number to invalidate any
lookup of an unhashed dentry.

So checking d_unhashed() is not incorrect, but it's not useful either:
the code has to work correctly even without it. So just remove it.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/dcache.c b/fs/dcache.c
index 539943e..c4d2ff8 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1871,8 +1871,6 @@ seqretry:
 		seq = raw_seqcount_begin(&dentry->d_seq);
 		if (dentry->d_parent != parent)
 			continue;
-		if (d_unhashed(dentry))
-			continue;
 		*seqp = seq;
 
 		if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
-- 
cgit v0.10.2


From 94753db5ed9ad97582ef453127d9626a7a2be602 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 10 May 2012 12:19:19 -0700
Subject: vfs: do the careful dentry name access for all dentry_cmp cases

Commit 12f8ad4b0533 ("vfs: clean up __d_lookup_rcu() and dentry_cmp()
interfaces") did the careful ACCESS_ONCE() of the dentry name only for
the word-at-a-time case, even though the issue is generic.

Admittedly I don't really see gcc ever reloading the value in the middle
of the loop, so the ACCESS_ONCE() protects us from a fairly theoretical
issue. But better safe than sorry.

Also, this consolidates the common parts of the word-at-a-time and
bytewise logic, which includes checking the length.  We'll be changing
that later.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/dcache.c b/fs/dcache.c
index c4d2ff8..5c09ad7 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -153,30 +153,9 @@ int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,
  * In contrast, 'ct' and 'tcount' can be from a pathname, and do
  * need the careful unaligned handling.
  */
-static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
+static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
 {
 	unsigned long a,b,mask;
-	const unsigned char *cs;
-
-	if (unlikely(dentry->d_name.len != tcount))
-		return 1;
-	/*
-	 * Be careful about RCU walk racing with rename:
-	 * use ACCESS_ONCE to fetch the name pointer.
-	 *
-	 * NOTE! Even if a rename will mean that the length
-	 * was not loaded atomically, we don't care. The
-	 * RCU walk will check the sequence count eventually,
-	 * and catch it. And we won't overrun the buffer,
-	 * because we're reading the name pointer atomically,
-	 * and a dentry name is guaranteed to be properly
-	 * terminated with a NUL byte.
-	 *
-	 * End result: even if 'len' is wrong, we'll exit
-	 * early because the data cannot match (there can
-	 * be no NUL in the ct/tcount data)
-	 */
-	cs = ACCESS_ONCE(dentry->d_name.name);
 
 	for (;;) {
 		a = *(unsigned long *)cs;
@@ -197,13 +176,8 @@ static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *c
 
 #else
 
-static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
+static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
 {
-	const unsigned char *cs = dentry->d_name.name;
-
-	if (dentry->d_name.len != tcount)
-		return 1;
-
 	do {
 		if (*cs != *ct)
 			return 1;
@@ -216,6 +190,30 @@ static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *c
 
 #endif
 
+static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
+{
+	if (dentry->d_name.len != tcount)
+		return 1;
+
+	/*
+	 * Be careful about RCU walk racing with rename:
+	 * use ACCESS_ONCE to fetch the name pointer.
+	 *
+	 * NOTE! Even if a rename will mean that the length
+	 * was not loaded atomically, we don't care. The
+	 * RCU walk will check the sequence count eventually,
+	 * and catch it. And we won't overrun the buffer,
+	 * because we're reading the name pointer atomically,
+	 * and a dentry name is guaranteed to be properly
+	 * terminated with a NUL byte.
+	 *
+	 * End result: even if 'len' is wrong, we'll exit
+	 * early because the data cannot match (there can
+	 * be no NUL in the ct/tcount data)
+	 */
+	return dentry_string_cmp(ACCESS_ONCE(dentry->d_name.name), ct, tcount);
+}
+
 static void __d_free(struct rcu_head *head)
 {
 	struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
-- 
cgit v0.10.2


From ee983e89670704b2a05e897b161f2674a42d1508 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 10 May 2012 12:37:10 -0700
Subject: vfs: move dentry name length comparison from dentry_cmp() into
 callers

All callers do want to check the dentry length, but some of them can
check the length and the hash together, so doing it in dentry_cmp() can
be counter-productive.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/dcache.c b/fs/dcache.c
index 5c09ad7..e6707a1 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -192,9 +192,6 @@ static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char
 
 static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
 {
-	if (dentry->d_name.len != tcount)
-		return 1;
-
 	/*
 	 * Be careful about RCU walk racing with rename:
 	 * use ACCESS_ONCE to fetch the name pointer.
@@ -1464,6 +1461,8 @@ static struct dentry *__d_instantiate_unique(struct dentry *entry,
 			continue;
 		if (alias->d_parent != entry->d_parent)
 			continue;
+		if (alias->d_name.len != len)
+			continue;
 		if (dentry_cmp(alias, name, len))
 			continue;
 		__dget(alias);
@@ -1882,6 +1881,8 @@ seqretry:
 			}
 		}
 
+		if (dentry->d_name.len != len)
+			continue;
 		if (!dentry_cmp(dentry, str, len))
 			return dentry;
 	}
@@ -1984,6 +1985,8 @@ struct dentry *__d_lookup(struct dentry *parent, struct qstr *name)
 						tlen, tname, name))
 				goto next;
 		} else {
+			if (dentry->d_name.len != len)
+				goto next;
 			if (dentry_cmp(dentry, str, len))
 				goto next;
 		}
-- 
cgit v0.10.2


From 26fe575028703948880fce4355a210c76bb0536e Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 10 May 2012 13:14:12 -0700
Subject: vfs: make it possible to access the dentry hash/len as one 64-bit
 entry

This allows comparing hash and len in one operation on 64-bit
architectures.  Right now only __d_lookup_rcu() takes advantage of this,
since that is the case we care most about.

The use of anonymous struct/unions hides the alternate 64-bit approach
from most users, the exception being a few cases where we initialize a
'struct qstr' with a static initializer.  This makes the problematic
cases use a new QSTR_INIT() helper function for that (but initializing
just the name pointer with a "{ .name = xyzzy }" initializer remains
valid, as does just copying another qstr structure).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/dcache.c b/fs/dcache.c
index e6707a1..92099f6 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1502,7 +1502,7 @@ struct dentry *d_make_root(struct inode *root_inode)
 	struct dentry *res = NULL;
 
 	if (root_inode) {
-		static const struct qstr name = { .name = "/", .len = 1 };
+		static const struct qstr name = QSTR_INIT("/", 1);
 
 		res = __d_alloc(root_inode->i_sb, &name);
 		if (res)
@@ -1816,10 +1816,9 @@ struct dentry *__d_lookup_rcu(const struct dentry *parent,
 				const struct qstr *name,
 				unsigned *seqp, struct inode *inode)
 {
-	unsigned int len = name->len;
-	unsigned int hash = name->hash;
+	u64 hashlen = name->hash_len;
 	const unsigned char *str = name->name;
-	struct hlist_bl_head *b = d_hash(parent, hash);
+	struct hlist_bl_head *b = d_hash(parent, hashlen_hash(hashlen));
 	struct hlist_bl_node *node;
 	struct dentry *dentry;
 
@@ -1846,9 +1845,6 @@ struct dentry *__d_lookup_rcu(const struct dentry *parent,
 	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
 		unsigned seq;
 
-		if (dentry->d_name.hash != hash)
-			continue;
-
 seqretry:
 		/*
 		 * The dentry sequence count protects us from concurrent
@@ -1871,6 +1867,8 @@ seqretry:
 		*seqp = seq;
 
 		if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
+			if (dentry->d_name.hash != hashlen_hash(hashlen))
+				continue;
 			switch (slow_dentry_cmp(parent, inode, dentry, seq, name)) {
 			case D_COMP_OK:
 				return dentry;
@@ -1881,9 +1879,9 @@ seqretry:
 			}
 		}
 
-		if (dentry->d_name.len != len)
+		if (dentry->d_name.hash_len != hashlen)
 			continue;
-		if (!dentry_cmp(dentry, str, len))
+		if (!dentry_cmp(dentry, str, hashlen_len(hashlen)))
 			return dentry;
 	}
 	return NULL;
diff --git a/fs/ext2/namei.c b/fs/ext2/namei.c
index dffb865..f663a67 100644
--- a/fs/ext2/namei.c
+++ b/fs/ext2/namei.c
@@ -79,7 +79,7 @@ static struct dentry *ext2_lookup(struct inode * dir, struct dentry *dentry, str
 
 struct dentry *ext2_get_parent(struct dentry *child)
 {
-	struct qstr dotdot = {.name = "..", .len = 2};
+	struct qstr dotdot = QSTR_INIT("..", 2);
 	unsigned long ino = ext2_inode_by_name(child->d_inode, &dotdot);
 	if (!ino)
 		return ERR_PTR(-ENOENT);
diff --git a/fs/ext3/namei.c b/fs/ext3/namei.c
index d7940b2..eeb63df 100644
--- a/fs/ext3/namei.c
+++ b/fs/ext3/namei.c
@@ -1045,7 +1045,7 @@ static struct dentry *ext3_lookup(struct inode * dir, struct dentry *dentry, str
 struct dentry *ext3_get_parent(struct dentry *child)
 {
 	unsigned long ino;
-	struct qstr dotdot = {.name = "..", .len = 2};
+	struct qstr dotdot = QSTR_INIT("..", 2);
 	struct ext3_dir_entry_2 * de;
 	struct buffer_head *bh;
 
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 349d7b3..e2a3f4b 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1052,10 +1052,7 @@ static struct dentry *ext4_lookup(struct inode *dir, struct dentry *dentry, stru
 struct dentry *ext4_get_parent(struct dentry *child)
 {
 	__u32 ino;
-	static const struct qstr dotdot = {
-		.name = "..",
-		.len = 2,
-	};
+	static const struct qstr dotdot = QSTR_INIT("..", 2);
 	struct ext4_dir_entry_2 * de;
 	struct buffer_head *bh;
 
diff --git a/fs/gfs2/dir.c b/fs/gfs2/dir.c
index a836056..8aaeb07 100644
--- a/fs/gfs2/dir.c
+++ b/fs/gfs2/dir.c
@@ -821,7 +821,7 @@ static struct gfs2_leaf *new_leaf(struct inode *inode, struct buffer_head **pbh,
 	struct buffer_head *bh;
 	struct gfs2_leaf *leaf;
 	struct gfs2_dirent *dent;
-	struct qstr name = { .name = "", .len = 0, .hash = 0 };
+	struct qstr name = { .name = "" };
 
 	error = gfs2_alloc_blocks(ip, &bn, &n, 0, NULL);
 	if (error)
diff --git a/fs/libfs.c b/fs/libfs.c
index 18d08f5..f86ec27 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -68,7 +68,7 @@ struct dentry *simple_lookup(struct inode *dir, struct dentry *dentry, struct na
 
 int dcache_dir_open(struct inode *inode, struct file *file)
 {
-	static struct qstr cursor_name = {.len = 1, .name = "."};
+	static struct qstr cursor_name = QSTR_INIT(".", 1);
 
 	file->private_data = d_alloc(file->f_path.dentry, &cursor_name);
 
@@ -225,7 +225,7 @@ struct dentry *mount_pseudo(struct file_system_type *fs_type, char *name,
 	struct super_block *s = sget(fs_type, NULL, set_anon_super, NULL);
 	struct dentry *dentry;
 	struct inode *root;
-	struct qstr d_name = {.name = name, .len = strlen(name)};
+	struct qstr d_name = QSTR_INIT(name, strlen(name));
 
 	if (IS_ERR(s))
 		return ERR_CAST(s);
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 8789210..eedd24d 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -477,10 +477,7 @@ different:
 static
 void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry)
 {
-	struct qstr filename = {
-		.len = entry->len,
-		.name = entry->name,
-	};
+	struct qstr filename = QSTR_INIT(entry->name, entry->len);
 	struct dentry *dentry;
 	struct dentry *alias;
 	struct inode *dir = parent->d_inode;
diff --git a/fs/nfs/nfs3proc.c b/fs/nfs/nfs3proc.c
index 5242eae..75c6829 100644
--- a/fs/nfs/nfs3proc.c
+++ b/fs/nfs/nfs3proc.c
@@ -398,8 +398,7 @@ nfs3_proc_remove(struct inode *dir, struct qstr *name)
 {
 	struct nfs_removeargs arg = {
 		.fh = NFS_FH(dir),
-		.name.len = name->len,
-		.name.name = name->name,
+		.name = *name,
 	};
 	struct nfs_removeres res;
 	struct rpc_message msg = {
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 99650aa..ab985f6 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -2782,8 +2782,7 @@ static int _nfs4_proc_remove(struct inode *dir, struct qstr *name)
 	struct nfs_server *server = NFS_SERVER(dir);
 	struct nfs_removeargs args = {
 		.fh = NFS_FH(dir),
-		.name.len = name->len,
-		.name.name = name->name,
+		.name = *name,
 		.bitmask = server->attr_bitmask,
 	};
 	struct nfs_removeres res = {
diff --git a/fs/nfs/proc.c b/fs/nfs/proc.c
index b63b6f4..d6408b6 100644
--- a/fs/nfs/proc.c
+++ b/fs/nfs/proc.c
@@ -335,8 +335,7 @@ nfs_proc_remove(struct inode *dir, struct qstr *name)
 {
 	struct nfs_removeargs arg = {
 		.fh = NFS_FH(dir),
-		.name.len = name->len,
-		.name.name = name->name,
+		.name = *name,
 	};
 	struct rpc_message msg = { 
 		.rpc_proc = &nfs_procedures[NFSPROC_REMOVE],
diff --git a/fs/nilfs2/namei.c b/fs/nilfs2/namei.c
index fce2bbe..0bb2c20 100644
--- a/fs/nilfs2/namei.c
+++ b/fs/nilfs2/namei.c
@@ -441,7 +441,7 @@ static struct dentry *nilfs_get_parent(struct dentry *child)
 {
 	unsigned long ino;
 	struct inode *inode;
-	struct qstr dotdot = {.name = "..", .len = 2};
+	struct qstr dotdot = QSTR_INIT("..", 2);
 	struct nilfs_root *root;
 
 	ino = nilfs_inode_by_name(child->d_inode, &dotdot);
diff --git a/fs/ubifs/tnc.c b/fs/ubifs/tnc.c
index 16ad84d..abd5133 100644
--- a/fs/ubifs/tnc.c
+++ b/fs/ubifs/tnc.c
@@ -2361,7 +2361,7 @@ int ubifs_tnc_add_nm(struct ubifs_info *c, const union ubifs_key *key,
 			 * by passing 'ubifs_tnc_remove_nm()' the same key but
 			 * an unmatchable name.
 			 */
-			struct qstr noname = { .len = 0, .name = "" };
+			struct qstr noname = { .name = "" };
 
 			err = dbg_check_tnc(c, 0);
 			mutex_unlock(&c->tnc_mutex);
diff --git a/fs/ubifs/xattr.c b/fs/ubifs/xattr.c
index 85b2722..7a8bafa 100644
--- a/fs/ubifs/xattr.c
+++ b/fs/ubifs/xattr.c
@@ -298,7 +298,7 @@ int ubifs_setxattr(struct dentry *dentry, const char *name,
 {
 	struct inode *inode, *host = dentry->d_inode;
 	struct ubifs_info *c = host->i_sb->s_fs_info;
-	struct qstr nm = { .name = name, .len = strlen(name) };
+	struct qstr nm = QSTR_INIT(name, strlen(name));
 	struct ubifs_dent_node *xent;
 	union ubifs_key key;
 	int err, type;
@@ -361,7 +361,7 @@ ssize_t ubifs_getxattr(struct dentry *dentry, const char *name, void *buf,
 {
 	struct inode *inode, *host = dentry->d_inode;
 	struct ubifs_info *c = host->i_sb->s_fs_info;
-	struct qstr nm = { .name = name, .len = strlen(name) };
+	struct qstr nm = QSTR_INIT(name, strlen(name));
 	struct ubifs_inode *ui;
 	struct ubifs_dent_node *xent;
 	union ubifs_key key;
@@ -524,7 +524,7 @@ int ubifs_removexattr(struct dentry *dentry, const char *name)
 {
 	struct inode *inode, *host = dentry->d_inode;
 	struct ubifs_info *c = host->i_sb->s_fs_info;
-	struct qstr nm = { .name = name, .len = strlen(name) };
+	struct qstr nm = QSTR_INIT(name, strlen(name));
 	struct ubifs_dent_node *xent;
 	union ubifs_key key;
 	int err;
diff --git a/fs/udf/namei.c b/fs/udf/namei.c
index 38de8f2..a165c66 100644
--- a/fs/udf/namei.c
+++ b/fs/udf/namei.c
@@ -1193,7 +1193,7 @@ static struct dentry *udf_get_parent(struct dentry *child)
 {
 	struct kernel_lb_addr tloc;
 	struct inode *inode = NULL;
-	struct qstr dotdot = {.name = "..", .len = 2};
+	struct qstr dotdot = QSTR_INIT("..", 2);
 	struct fileIdentDesc cfi;
 	struct udf_fileident_bh fibh;
 
diff --git a/fs/ufs/super.c b/fs/ufs/super.c
index ac8e279..302f340 100644
--- a/fs/ufs/super.c
+++ b/fs/ufs/super.c
@@ -146,10 +146,7 @@ static struct dentry *ufs_fh_to_parent(struct super_block *sb, struct fid *fid,
 
 static struct dentry *ufs_get_parent(struct dentry *child)
 {
-	struct qstr dot_dot = {
-		.name	= "..",
-		.len	= 2,
-	};
+	struct qstr dot_dot = QSTR_INIT("..", 2);
 	ino_t ino;
 
 	ino = ufs_inode_by_name(child->d_inode, &dot_dot);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 8239f64..094789f 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -25,6 +25,13 @@ struct vfsmount;
 
 #define IS_ROOT(x) ((x) == (x)->d_parent)
 
+/* The hash is always the low bits of hash_len */
+#ifdef __LITTLE_ENDIAN
+ #define HASH_LEN_DECLARE u32 hash; u32 len;
+#else
+ #define HASH_LEN_DECLARE u32 len; u32 hash;
+#endif
+
 /*
  * "quick string" -- eases parameter passing, but more importantly
  * saves "metadata" about the string (ie length and the hash).
@@ -33,11 +40,19 @@ struct vfsmount;
  * dentry.
  */
 struct qstr {
-	unsigned int hash;
-	unsigned int len;
+	union {
+		struct {
+			HASH_LEN_DECLARE;
+		};
+		u64 hash_len;
+	};
 	const unsigned char *name;
 };
 
+#define QSTR_INIT(n,l) { { { .len = l } }, .name = n }
+#define hashlen_hash(hashlen) ((u32) (hashlen))
+#define hashlen_len(hashlen)  ((u32)((hashlen) >> 32))
+
 struct dentry_stat_t {
 	int nr_dentry;
 	int nr_unused;
diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index adf2990..7fee13b 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -127,9 +127,7 @@ static struct dentry *rpc_setup_pipedir_sb(struct super_block *sb,
 {
 	static uint32_t clntid;
 	char name[15];
-	struct qstr q = {
-		.name = name,
-	};
+	struct qstr q = { .name = name };
 	struct dentry *dir, *dentry;
 	int error;
 
diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index 3b62cf2..fd24239 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -1059,12 +1059,9 @@ static const struct rpc_filelist files[] = {
 struct dentry *rpc_d_lookup_sb(const struct super_block *sb,
 			       const unsigned char *dir_name)
 {
-	struct qstr dir = {
-		.name = dir_name,
-		.len = strlen(dir_name),
-		.hash = full_name_hash(dir_name, strlen(dir_name)),
-	};
+	struct qstr dir = QSTR_INIT(dir_name, strlen(dir_name));
 
+	dir.hash = full_name_hash(dir.name, dir.len);
 	return d_lookup(sb->s_root, &dir);
 }
 EXPORT_SYMBOL_GPL(rpc_d_lookup_sb);
-- 
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