Re: [2.6.16 PATCH] Filessytem Events Reporter V3

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Evgeniy Polyakov wrote:
On Tue, Apr 11, 2006 at 04:59:18PM +0800, Yi Yang ([email protected]) wrote:

+		if (skb->len >= FSEVENT_FILTER_MSGSIZE) {
I'm not sure about your size checks.
I think it should be compared with nlhdr->nlmsg_len?
At this point, skb->len  should be the same as nlhdr->nlmsg_len.
Hmm, skb->len includes size of netlink header, but nlhdr->nlmsg_len does
not.
No, it  included length of netlink header, please see it.
struct nlmsghdr
{
__u32 nlmsg_len; /* Length of message including header */
       __u16           nlmsg_type;     /* Message content */
       __u16           nlmsg_flags;    /* Additional flags */
       __u32           nlmsg_seq;      /* Sequence number */
       __u32           nlmsg_pid;      /* Sending process PID */
};
+#define DEFINE_FILTER_MATCH_FUNC(filtertype, key) 			\
+	static int match_##filtertype(listener * p,			\
+				struct fsevent * event,			\
+				struct sk_buff * skb)			\
+	{								\
+		int ret = 0;						\
+		filtertype * xfilter = NULL;				\
+		struct sk_buff * skb2 = NULL;				\
+		struct list_head *  head = &(p->key##_filter_list_head);  \
+		list_for_each_entry(xfilter, head, list) {		\
+			if (xfilter->key != event->key)			\
+				continue;				\
+			ret = filter_fsevent(xfilter->mask, event->type); \
+			if ( ret != 0)					\
+				return -1;				\
+			skb2 = skb_clone(skb, GFP_KERNEL);		\
+       			if (skb2 == NULL)			 \
Coding style.

+				return -1;				\
+			NETLINK_CB(skb2).dst_group = 0;			\
+			NETLINK_CB(skb2).dst_pid = p->pid;		\
+			NETLINK_CB(skb2).pid = 0;			\
+			return (netlink_unicast(fsevent_sock, skb2,	\
+					p->pid, MSG_DONTWAIT));		\
+		}							\
+		return -1;						\
+	}								\
+
+DEFINE_FILTER_MATCH_FUNC(pid_filter, pid)
+
+DEFINE_FILTER_MATCH_FUNC(uid_filter, uid)
+
+DEFINE_FILTER_MATCH_FUNC(gid_filter, gid)
You send the same data for each type of filters, maybe it is design
approach, but why don't you want to send that data in one skb?
netlink control block is not the same, netlink_broadcast is a typical case.
Yes, I see, pid is changed.

+#define MATCH_XID(key, listenerp, event, skb) 			\
+	ret = match_##key##_filter(listenerp, event, skb); 	\
+	if (ret == 0) {					 	\
+		kfree_skb(skb);				 	\
+	        continue;				 	\
Your match funtions can not return 0.
It can, if sending is successfull, netlink_unicast will return 0.
No, it returns skb->len on success.
netlink_broadcast() returns 0 on success.

+static void __exit fsevent_exit(void)
+{
+	listener * p = NULL, * q = NULL;
+	int cpu;
+	int wait_flag = 0;
+	struct sk_buff_head * skb_head = NULL;
+
+	fsevents_mask = 0;
+	_raise_fsevent = 0;
+	exit_flag = 1;
+
+	for_each_cpu(cpu)
+		schedule_work(&per_cpu(fsevent_work, cpu));
+
+	while (1) {
+		wait_flag = 0;
+		for_each_cpu(cpu) {
+			skb_head = &per_cpu(fsevent_send_queue, cpu);
+			if (skb_head->qlen != 0) {
+				wait_flag = 1;
+				break;
+			}
+		}
+		if (wait_flag == 1) {
+			set_current_state(TASK_INTERRUPTIBLE);
+			schedule_timeout(HZ/10);
+		} else
+			break;
+	}
This is still broken.
You race with schedule_work() in this loop. It requires
flush_scheduled_work().

And I still have soume doubts about __raise_fsevent().
What if you set fsevents_mask to zero after __raise_fsevent() is
started, but not yet queued an skb, and above loop and scheduled work
are completed?
I think it is OK, schedule_timeout will release cpu to work queues, work queues should have enough time
to finish their works, I don't know what is your reason.
It is not guaranteed that scheduled work will be processed until
flush_scheduled_work() completion, no matter how many times processor
has idle cycles.

Second issue is that both above loop and work can be finished, but some
__raise_fsevent() will be still in progress.
I knew your meaning, if you have a better way, tell me.
You need some type of completion of the last worker...

+	atomic_set(&fsevent_sock->sk_rmem_alloc, 0);
+	atomic_set(&fsevent_sock->sk_wmem_alloc, 0);
This is really wrong, since it hides skb processing errors like double
freeing or leaks.
If userspace application terminated exceptionally, there are some skbs not to be consumed on socket, so if you rmmod it, sock_release will report some failure information, the above two statements will remove this
error.
All queues will be flushed, when socket is freed, and if sock_release() shows
that assertion is failed, this definitely means you broke socket accounting, for example freed skb two times.
I searched those code, it didn't decrease sk_rmem_alloc, do you mean skb_queue_purge will decrease it?
+	sock_release(fsevent_sock->sk_socket);
...

Btw, it would be nice to have some kind of microbenchmark,
like http://permalink.gmane.org/gmane.linux.kernel/292755
just to see how things go...
I have a userspace application to test fsevent, I'll release it to community in order to find more issues on
fsevent.
And please publish some numbers so people could make some prognosis of
system behaviour.
Do you mean perfornance indice?

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