Date:	Fri,  5 Dec 2008 10:55:02 -0800
From:	Inaky Perez-Gonzalez <inaky@...ux.intel.com>
To:	netdev@...r.kernel.org
Cc:	wimax@...uxwimax.org, greg@...ah.com
Subject: [PATCH 09/40] wimax: Mappping of generic netlink family IDs to net devices

Low overhead method to map generic netlink family IDs to the WiMAX
device attached to them that optimizes for the case where most systems
have a single WiMAX device, or at most, a very low number of WiMAX
adaptors.

Signed-off-by: Inaky Perez-Gonzalez <inaky@...ux.intel.com>
---
 net/wimax/id-table.c |  140 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 140 insertions(+), 0 deletions(-)
 create mode 100644 net/wimax/id-table.c

diff --git a/net/wimax/id-table.c b/net/wimax/id-table.c
new file mode 100644
index 0000000..0f5fe85
--- /dev/null
+++ b/net/wimax/id-table.c
@@ -0,0 +1,140 @@
+/*
+ * Linux WiMAX
+ * Mappping of generic netlink family IDs to net devices
+ *
+ *
+ * Copyright (C) 2005-2006 Intel Corporation <linux-wimax@...el.com>
+ * Inaky Perez-Gonzalez <inaky.perez-gonzalez@...el.com>
+ *
+ * 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.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ *
+ * We assign a single generic netlink family ID to each device (to
+ * simplify lookup).
+ *
+ * We need a way to map family ID to a wimax_dev pointer.
+ *
+ * The idea is to use a very simple lookup. Using a netlink attribute
+ * with (for example) the interface name implies a heavier search over
+ * all the network devices; seemed kind of a waste given that we know
+ * we are looking for a WiMAX device and that most systems will have
+ * just a single WiMAX adapter.
+ *
+ * We put all the WiMAX devices in the system in a linked list and
+ * match the generic link family ID against the list.
+ *
+ * By using a linked list, the case of a single adapter in the system
+ * becomes (almost) no overhead, while still working for many more. If
+ * it ever goes beyond two, I'll be surprised.
+ */
+#include <linux/device.h>
+#include <net/genetlink.h>
+#include <linux/netdevice.h>
+#include <linux/list.h>
+#include <linux/wimax.h>
+#include "wimax-internal.h"
+
+
+#define D_SUBMODULE id_table
+#include "debug-levels.h"
+
+
+static DEFINE_SPINLOCK(wimax_id_table_lock);
+static struct list_head wimax_id_table = LIST_HEAD_INIT(wimax_id_table);
+
+
+/*
+ * wimax_id_table_add - add a gennetlink familiy ID / wimax_dev mapping
+ *
+ * @wimax_dev: WiMAX device descriptor to associate to the Generic
+ *     Netlink family ID.
+ *
+ * Look for an empty spot in the ID table; if none found, double the
+ * table's size and get the first spot.
+ */
+void wimax_id_table_add(struct wimax_dev *wimax_dev)
+{
+	d_fnstart(3, NULL, "(wimax_dev %p)\n", wimax_dev);
+	spin_lock(&wimax_id_table_lock);
+	list_add(&wimax_dev->id_table_node, &wimax_id_table);
+	spin_unlock(&wimax_id_table_lock);
+	d_fnend(3, NULL, "(wimax_dev %p)\n", wimax_dev);
+}
+
+
+/*
+ * wimax_get_netdev_by_info - lookup a wimax_dev from the gennetlink info
+ *
+ * The generic netlink family ID has been filled out in the
+ * nlmsghdr->nlmsg_type field, so we pull it from there, look it up in
+ * the mapping table and reference the wimax_dev.
+ *
+ * When done, the reference should be dropped with
+ * 'dev_put(wimax_dev->net_dev)'.
+ */
+struct wimax_dev *wimax_dev_get_by_genl_info(struct genl_info *info)
+{
+	struct wimax_dev *wimax_dev = NULL;
+	int id = info->nlhdr->nlmsg_type;
+
+	d_fnstart(3, NULL, "(info %p [id %d])\n", info, id);
+	spin_lock(&wimax_id_table_lock);
+	list_for_each_entry(wimax_dev, &wimax_id_table, id_table_node) {
+		if (wimax_dev->gnl_family.id == id) {
+			dev_hold(wimax_dev->net_dev);
+			break;
+		}
+	}
+	if (wimax_dev == NULL)
+		d_printf(1, NULL, "wimax: no device associated to ID %d\n", id);
+	spin_unlock(&wimax_id_table_lock);
+	d_fnend(3, NULL, "(info %p) = %p\n", info, wimax_dev);
+	return wimax_dev;
+}
+
+
+/*
+ * wimax_id_table_rm - Remove a gennetlink familiy ID / wimax_dev mapping
+ *
+ * @id: family ID to remove from the table
+ */
+void wimax_id_table_rm(struct wimax_dev *wimax_dev)
+{
+	spin_lock(&wimax_id_table_lock);
+	list_del_init(&wimax_dev->id_table_node);
+	spin_unlock(&wimax_id_table_lock);
+}
+
+
+/*
+ * Release the gennetlink family id / mapping table
+ *
+ * On debug, verify that the table is empty upon removal.
+ */
+void wimax_id_table_release(void)
+{
+#ifndef CONFIG_BUG
+	return;
+#endif
+	struct wimax_dev *wimax_dev;
+
+	spin_lock(&wimax_id_table_lock);
+	list_for_each_entry(wimax_dev, &wimax_id_table, id_table_node) {
+		printk(KERN_ERR "BUG: %s wimax_dev %p id %u not cleared\n",
+		       __func__, wimax_dev, wimax_dev->gnl_family.id);
+		WARN_ON(1);
+	}
+	spin_unlock(&wimax_id_table_lock);
+}
-- 
1.5.6.5

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