backports: add rhashtable_walk_init()

Since commit 1068c678f "rhashtable: accept GFP flags in
rhashtable_walk_init" rhashtable_walk_init() takes an additional
parameter which is also used by the mac80211 code, so backport the
function. For kernel < 4.1 this is not needed, because we already ship
a recent version of rhashtable. Add rhashtable_walk_init() instead of
adding the complete rhashtable to same some space on recent kernel
versions.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

2 files changed, 63 insertions, 0 deletions

diff --git a/backport/compat/Makefile b/backport/compat/Makefile
index 7651f83d..6013083e 100644
--- a/backport/compat/Makefile
+++ b/backport/compat/Makefile
@@ -32,6 +32,7 @@ compat-$(CPTCFG_KERNEL_4_3) += backport-4.3.o
 compat-$(CPTCFG_KERNEL_4_4) += backport-4.4.o
 compat-$(CPTCFG_KERNEL_4_5) += backport-4.5.o
 compat-$(CPTCFG_KERNEL_4_6) += backport-4.6.o
+compat-$(CPTCFG_KERNEL_4_7) += backport-4.7.o
 
 compat-$(CPTCFG_BPAUTO_BUILD_CRYPTO_CCM) += crypto-ccm.o
 compat-$(CPTCFG_BPAUTO_CRYPTO_SKCIPHER) += crypto-skcipher.o
diff --git a/backport/compat/backport-4.7.c b/backport/compat/backport-4.7.c
new file mode 100644
index 00000000..04737b04
--- /dev/null
+++ b/backport/compat/backport-4.7.c
@@ -0,0 +1,62 @@
+/*
+ * Copyright(c) 2016 Hauke Mehrtens <hauke@hauke-m.de>
+ *
+ * Backport functionality introduced in Linux 4.7.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/export.h>
+#include <linux/list.h>
+#include <linux/rcupdate.h>
+#include <linux/rhashtable.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4,1,0)
+/**
+ * rhashtable_walk_init - Initialise an iterator
+ * @ht:		Table to walk over
+ * @iter:	Hash table Iterator
+ * @gfp:	GFP flags for allocations
+ *
+ * This function prepares a hash table walk.
+ *
+ * Note that if you restart a walk after rhashtable_walk_stop you
+ * may see the same object twice.  Also, you may miss objects if
+ * there are removals in between rhashtable_walk_stop and the next
+ * call to rhashtable_walk_start.
+ *
+ * For a completely stable walk you should construct your own data
+ * structure outside the hash table.
+ *
+ * This function may sleep so you must not call it from interrupt
+ * context or with spin locks held.
+ *
+ * You must call rhashtable_walk_exit if this function returns
+ * successfully.
+ */
+int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter,
+			 gfp_t gfp)
+{
+	iter->ht = ht;
+	iter->p = NULL;
+	iter->slot = 0;
+	iter->skip = 0;
+
+	iter->walker = kmalloc(sizeof(*iter->walker), gfp);
+	if (!iter->walker)
+		return -ENOMEM;
+
+	spin_lock(&ht->lock);
+	iter->walker->tbl =
+		rcu_dereference_protected(ht->tbl, lockdep_is_held(&ht->lock));
+	list_add(&iter->walker->list, &iter->walker->tbl->walkers);
+	spin_unlock(&ht->lock);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(rhashtable_walk_init);
+#endif /* >= 4.1 */