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    SubjectRe: [2.6.16 PATCH] Filessytem Events Reporter V2
    On Wed, Apr 05, 2006 at 09:21:26PM +0800, Yi Yang (yang.y.yi@gmail.com) wrote:
    > Compared with Filesystem Events Reporter v1, the following changes are done:
    > - Use workqueue/keventd instead of kfseventd.
    > - fsevent_mask can be set by sysctl and proc
    > interface.
    > - Add missed spinlock
    > - Ensure fsevent sequence number is uniqe
    >
    > This patch implements a filsystem events report facitily, Filesystem Events
    > Reporter, the user can monitor filesystem activities via it, currently, it
    > can monitor access, attribute change, open, create, modify, delete,
    > move and close of any file or directory as well as mount/umount.

    Comments below.

    ...
    > +
    > +static int fsevent_ack(enum fsevent_type type, pid_t pid, u32 seq)
    > +{
    > + struct fsevent *event;
    > + unsigned int size;
    > + struct sk_buff * skb = NULL;
    > + struct nlmsghdr * nlhdr = NULL;
    > +
    > + size = NLMSG_SPACE(sizeof(struct fsevent));
    > +
    > + skb = alloc_skb(size, GFP_KERNEL);
    > + if (!skb)
    > + return -ENOMEM;
    > +
    > + nlhdr = NLMSG_PUT(skb, 0, seq, NLMSG_DONE, size - sizeof(*nlhdr));
    > + event = NLMSG_DATA(nlhdr);
    > +
    > + ktime_get_ts(&event->timestamp);
    > + event->cpu = -1;
    > + event->type = type;
    > + event->pid = 0;
    > + event->uid = 0;
    > + event->gid = 0;
    > + event->len = 0;
    > + event->pname_len = 0;
    > + event->fname_len = 0;
    > + event->new_fname_len = 0;
    > + event->err = 0;
    > +
    > + NETLINK_CB(skb).dst_group = 0;
    > + NETLINK_CB(skb).dst_pid = pid;
    > + NETLINK_CB(skb).pid = 0;
    > +
    > + return (netlink_unicast(fsevent_sock, skb, pid, MSG_DONTWAIT));

    netlink_unicast() uses boolean value but ont MSG_* flags for nonblocking,
    so this should be netlink_unicast(fsevent_sock, skb, pid, 0);

    > +nlmsg_failure:
    > + kfree_skb(skb);
    > + return -1;
    > +}

    ...

    > +static void fsevent_recv(struct sock *sk, int len)
    > +{
    > + struct sk_buff *skb = NULL;
    > + struct nlmsghdr *nlhdr = NULL;
    > + struct fsevent_filter * filter = NULL;
    > + pid_t pid;
    > +
    > + while ((skb = skb_dequeue(&sk->sk_receive_queue)) != NULL) {
    > + skb_get(skb);
    > + if (skb->len >= FSEVENT_FILTER_MSGSIZE) {
    > + nlhdr = (struct nlmsghdr *)skb->data;
    > + filter = NLMSG_DATA(nlhdr);
    > + pid = NETLINK_CREDS(skb)->pid;
    > + if (find_fsevent_listener(pid) == NULL)
    > + atomic_inc(&fsevent_listener_num);
    > + set_fsevent_filter(filter, pid);

    What is the logic behind this steps?
    If there are no listeners you increment it's number no matter if it will
    or not be added in set_fsevent_filter().

    > + }
    > + kfree_skb(skb);
    > + }
    > +}
    > +
    > +#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) \
    > + return -ENOMEM; \
    > + 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)); \

    The same issue about nonblocking sending.

    > + } \
    > + return -ENODEV; \
    > + } \
    > +
    > +DEFINE_FILTER_MATCH_FUNC(pid_filter, pid)
    > +
    > +DEFINE_FILTER_MATCH_FUNC(uid_filter, uid)
    > +
    > +DEFINE_FILTER_MATCH_FUNC(gid_filter, gid)
    > +
    > +#define MATCH_XID(key, listenerp, event, skb) \
    > + ret = match_##key##_filter(listenerp, event, skb); \
    > + if (ret == 0) { \
    > + kfree_skb(skb); \
    > + continue; \
    > + } \
    > + do {} while (0) \
    > +
    > +static int fsevent_send_to_process(struct sk_buff * skb)
    > +{
    > + listener * p = NULL, * q = NULL;
    > + struct fsevent * event = NULL;
    > + struct sk_buff * skb2 = NULL;
    > + int ret = 0;
    > +
    > + event = (struct fsevent *)(skb->data + sizeof(struct nlmsghdr));
    > + spin_lock(&listener_list_lock);
    > + list_for_each_entry_safe(p, q, &listener_list_head, list) {
    > + MATCH_XID(pid, p, event, skb);
    > + MATCH_XID(uid, p, event, skb);
    > + MATCH_XID(gid, p, event, skb);
    > +
    > + if (filter_fsevent(p->mask, event->type) == 0) {
    > + skb2 = skb_clone(skb, GFP_KERNEL);
    > + if (skb2 == NULL)
    > + return -ENOMEM;
    > + NETLINK_CB(skb2).dst_group = 0;
    > + NETLINK_CB(skb2).dst_pid = p->pid;
    > + NETLINK_CB(skb2).pid = 0;
    > + ret = netlink_unicast(fsevent_sock, skb2,
    > + p->pid, MSG_DONTWAIT);
    > + if (ret == -ECONNREFUSED) {
    > + atomic_dec(&fsevent_listener_num);
    > + cleanup_dead_listener(p);
    > + }
    > + }
    > + }
    > + spin_unlock(&listener_list_lock);
    > + return ret;
    > +}
    > +
    > +static void fsevent_commit(void * unused)
    > +{
    > + struct sk_buff * skb = NULL;
    > +
    > + while((skb = skb_dequeue(&get_cpu_var(fsevent_send_queue)))
    > + != NULL) {
    > + fsevent_send_to_process(skb);
    > + put_cpu_var(fsevent_send_queue);
    > + }
    > +}

    Really strange mix of per-cpu variables for optimized performance and
    global spin locking.
    Consider using RCU for list of listeners.

    You use unicast delivery for netlink messages.
    According to my investigation [1], it's performance is better only when
    there is only one listener (or maybe two in some cases), but then it is
    noticebly slower than broadcasting.

    1. http://marc.theaimsgroup.com/?l=linux-netdev&m=114424884216006&w=2

    > +static struct ctl_table fsevent_mask_sysctl[] = {
    > + {
    > + .ctl_name = FSEVENT_MASK_CTL_NAME,
    > + .procname = "fsevent_mask",
    > + .data = &fsevents_mask,
    > + .maxlen = sizeof(u32),
    > + .mode = 0644,
    > + .proc_handler = &proc_dointvec,
    > + },
    > + { .ctl_name = 0 }
    > +};
    > +
    > +static struct ctl_table fs_root_sysctl[] = {
    > + {
    > + .ctl_name = CTL_FS,
    > + .procname = "fs",
    > + .mode = 0555,
    > + .child = fsevent_mask_sysctl,
    > + },
    > + { .ctl_name = 0 }
    > +};
    > +
    > +static int __init fsevent_init(void)
    > +{
    > + int cpu;
    > + struct sk_buff_head * listptr;
    > + struct work_struct * workptr;
    > +
    > + fsevent_sock = netlink_kernel_create(NETLINK_FSEVENT, 0,
    > + fsevent_recv, THIS_MODULE);
    > + if (!fsevent_sock)
    > + return -EIO;
    > + for_each_cpu(cpu) {
    > + listptr = &per_cpu(fsevent_send_queue, cpu);
    > + skb_queue_head_init(listptr);
    > + workptr = &per_cpu(fsevent_work, cpu);
    > + INIT_WORK(workptr, fsevent_commit, NULL);
    > + }

    Btw, you need some rebalancing of the per-cpu queues, probably in
    keventd, since CPUs can go offline and your messages will stuck foreve
    there.

    > + if (register_sysctl_table(fs_root_sysctl, 0) == NULL)
    > + return -ENOMEM;
    > +
    > + return 0;
    > +}
    > +
    > +static void __exit fsevent_exit(void)
    > +{
    > + listener * p = NULL, * q = NULL;
    > + sock_release(fsevent_sock->sk_socket);
    > + spin_lock(&listener_list_lock);
    > + list_for_each_entry_safe(p, q, &listener_list_head, list) {
    > + cleanup_dead_listener(p);
    > + }
    > + spin_unlock(&listener_list_lock);

    Broken. Your work can be pending on this stage, but you already removed
    and freed resources.

    > +}
    > +
    > +module_init(fsevent_init);
    > +module_exit(fsevent_exit);
    > +
    > +MODULE_LICENSE("GPL");
    > +MODULE_AUTHOR("Yi Yang <yang.y.yi@gmail.com>");
    > +MODULE_DESCRIPTION("File System Events Reporter");
    >

    --
    Evgeniy Polyakov
    -
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