Re: [RFC v3 1/4] fs: Add generic file system event notifications

+
+Sample request could look like the following:
+
+ echo /sample/mount/point G T 710000 500000 > /sys/fs/events/config
+
+Multiple request might be specified provided they are separated with semicolon.
+
+The configuration itself might be modified at any time. One can add/remove
+particular event types for given fielsystem, modify the threshold levels,
+and remove single or all entries from the 'config' file.
+
+ - Adding new event type:
+
+ $ echo MOUNT EVENT_TYPE > /sys/fs/events/config
+
+(Note that is is enough to provide the event type to be enabled without

+the already set ones.)
+
+ - Removing event type:
+
+ $ echo '!MOUNT EVENT_TYPE' > /sys/fs/events/config
+
+ - Updating threshold limits:
+
+ $ echo MOUNT T L1 L2 > /sys/fs/events/config
+
+ - Removing single entry:
+
+ $ echo '!MOUNT' > /sys/fs/events/config
+
+ - Removing all entries:
+
+ $ echo > /sys/fs/events/config
+
+Reading the file will list all registered entries with their current set-up
+along with some additional info like the filesystem type and the backing device
+name if available.
+
+Final, though a very important note on the configuration: when and if the
+actual events are being triggered falls way beyond the scope of the generic
+filesystem events interface. It is up to a particular filesystem
+implementation which events are to be supported - if any at all. So if
+given filesystem does not support the event notifications, an attempt to
+enable those through 'config' file will fail.
+
+
+3. The generic netlink interface support:
+=========================================
+
+Whenever an event notification is triggered (by given filesystem) the current
+configuration is being validated to decide whether a userpsace notification
+should be launched. If there has been no request (in a mean of 'config' file
+entry) for given event, one will be silently disregarded. If, on the other
+hand, someone is 'watching' given filesystem for specific events, a generic
+netlink message will be sent. A dedicated multicast group has been provided
+solely for this purpose so in order to receive such notifications, one should
+subscribe to this new multicast group. As for now only the init network
+namespace is being supported.
+
+3.1 Message format
+
+The FS_NL_C_EVENT shall be stored within the generic netlink message header
+as the command field. The message payload will provide more detailed info:
+the backing device major and minor numbers, the event code and the id of
+the process which action led to the event occurrence. In case of threshold
+notifications, the current number of available blocks will be included
+in the payload as well.
+
+
+	 0                   1                   2                   3
+	 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+	|	            NETLINK MESSAGE HEADER			|
+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+	| 		GENERIC NETLINK MESSAGE HEADER   		|
+	| 	   (with FS_NL_C_EVENT as genlmsghdr cdm field)		|

+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+	| 	      Optional user specific message header		|
+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+	|		   GENERIC MESSAGE PAYLOAD:			|
+	+---------------------------------------------------------------+
+	| 		  FS_NL_A_EVENT_ID  (NLA_U32)			|
+	+---------------------------------------------------------------+
+	|	  	  FS_NL_A_DEV_MAJOR (NLA_U32)			|
+	+---------------------------------------------------------------+
+	| 	  	  FS_NL_A_DEV_MINOR (NLA_U32) 			|
+	+---------------------------------------------------------------+
+	|  		  FS_NL_A_CAUSED_ID (NLA_U32)			|

+	+---------------------------------------------------------------+
+	|  		    FS_NL_A_DATA (NLA_U64)			|
+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+
+The above figure is based on:
+ http://www.linuxfoundation.org/collaborate/workgroups/networking/generic_netlink_howto#Message_Format
+
+

+	seq_putc(m, ' ');
+	if (sb->s_op->show_devname) {
+		sb->s_op->show_devname(m, en->mnt_path.mnt->mnt_root);
+	} else {
+		seq_escape(m, r_mnt->mnt_devname ? r_mnt->mnt_devname : "none",
+				" \t\n\\");
+	}
+	seq_puts(m, " (");
+
+	nmask = en->notify;
+	for (match = fs_etypes; match->pattern; ++match) {
+		if (match->token & nmask) {
+			seq_puts(m, match->pattern);

+			nmask &= ~match->token;
+			if (nmask)
+				seq_putc(m, ',');
+		}
+	}
+	seq_printf(m, " %llu %llu", en->th.lrange, en->th.urange);

+	seq_puts(m, ")\n");
+	return 0;
+}
+
+static const struct seq_operations fs_trace_seq_ops = {
+	.start	= fs_trace_seq_start,
+	.next	= fs_trace_seq_next,
+	.stop	= fs_trace_seq_stop,
+	.show	= fs_trace_seq_show,
+};
+
+static int fs_trace_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &fs_trace_seq_ops);
+}
+
+static const struct file_operations fs_trace_fops = {
+	.owner		= THIS_MODULE,
+	.open		= fs_trace_open,
+	.write		= fs_trace_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static int fs_trace_init(void)
+{
+	fs_trace_cachep = KMEM_CACHE(fs_trace_entry, 0);
+	if (!fs_trace_cachep)
+		return -EINVAL;
+	init_waitqueue_head(&trace_wq);
+	return 0;
+}
+
+/* VFS support */
+static int fs_trace_fill_super(struct super_block *sb, void *data, int silen)
+{
+	int ret;
+	static struct tree_descr desc[] = {
+		[2] = {
+			.name	= "config",
+			.ops	= &fs_trace_fops,
+			.mode	= S_IWUSR | S_IRUGO,
+		},
+		{""},
+	};
+
+	ret = simple_fill_super(sb, 0x7246332, desc);
+	return !ret ? fs_trace_init() : ret;
+}
+
+static struct dentry *fs_trace_do_mount(struct file_system_type *fs_type,
+		 int ntype, const char *dev_name, void *data)
+{
+	return mount_single(fs_type, ntype, data, fs_trace_fill_super);
+}
+
+static void fs_trace_kill_super(struct super_block *sb)
+{
+	/*
+	 * The rcu_barrier here will/should make sure all call_rcu
+	 * callbacks are completed - still there might be some active
+	 * trace objects in use which can make calling the
+	 * kmem_cache_destroy unsafe. So we wait until all traces
+	 * are finally released.
+	 */
+	fs_remove_all_traces();
+	rcu_barrier();
+	wait_event(trace_wq, !atomic_read(&stray_traces));
+
+	kmem_cache_destroy(fs_trace_cachep);
+	kill_litter_super(sb);
+}
+
+static struct kset	*fs_trace_kset;
+
+static struct file_system_type fs_trace_fstype = {
+	.name		= "fstrace",
+	.mount		= fs_trace_do_mount,
+	.kill_sb	= fs_trace_kill_super,
+};
+
+static void __init fs_trace_vfs_init(void)
+{
+	fs_trace_kset = kset_create_and_add("events", NULL, fs_kobj);
+
+	if (!fs_trace_kset)
+		return;
+
+	if (!register_filesystem(&fs_trace_fstype)) {
+		if (!fs_event_netlink_register())
+			return;
+		unregister_filesystem(&fs_trace_fstype);
+	}
+	kset_unregister(fs_trace_kset);
+}
+
+static int __init fs_trace_evens_init(void)
+{
+	fs_trace_vfs_init();
+	return 0;
+};
+module_init(fs_trace_evens_init);
+

diff --git a/fs/events/fs_event.h b/fs/events/fs_event.h
new file mode 100644
index 0000000..23f24c8
--- /dev/null
+++ b/fs/events/fs_event.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright(c) 2015 Samsung Electronics. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2.
+ *
+ * The full GNU General Public License is included in this distribution in the
+ * file called COPYING.
+ *
+ * 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.
+ */
+
+#ifndef __GENERIC_FS_EVENTS_H
+#define __GENERIC_FS_EVENTS_H
+
+int  fs_event_netlink_register(void);
+void fs_event_netlink_unregister(void);
+
+#endif /* __GENERIC_FS_EVENTS_H */

diff --git a/fs/events/fs_event_netlink.c b/fs/events/fs_event_netlink.c
new file mode 100644
index 0000000..0c97eb7
--- /dev/null
+++ b/fs/events/fs_event_netlink.c

@@ -0,0 +1,104 @@
+/*
+ * Copyright(c) 2015 Samsung Electronics. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2.
+ *
+ * The full GNU General Public License is included in this distribution in the
+ * file called COPYING.
+ *
+ * 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.
+ */
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <net/netlink.h>
+#include <net/genetlink.h>
+#include "fs_event.h"
+
+static const struct genl_multicast_group fs_event_mcgroups[] = {
+	{ .name = FS_EVENTS_MCAST_GRP_NAME, },
+};
+
+static struct genl_family fs_event_family = {
+	.id		= GENL_ID_GENERATE,
+	.name		= FS_EVENTS_FAMILY_NAME,
+	.version	= 1,
+	.maxattr	= FS_NL_A_MAX,
+	.mcgrps		= fs_event_mcgroups,
+	.n_mcgrps	= ARRAY_SIZE(fs_event_mcgroups),
+};
+
+int fs_netlink_send_event(size_t size, unsigned int event_id,
+			  int (*compose_msg)(struct sk_buff *skb,  void *data),
+			  void *cbdata)
+{
+	static atomic_t seq;
+	struct sk_buff *skb;
+	void *msg_head;
+	int ret = 0;
+
+	if (!size || !compose_msg)
+		return -EINVAL;
+
+	/* Skip if there are no listeners */
+	if (!genl_has_listeners(&fs_event_family, &init_net, 0))
+		return 0;
+
+	if (event_id != FS_EVENT_NONE)
+		size += nla_total_size(sizeof(u32));
+	size += nla_total_size(sizeof(u64));