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Date: Wed, 1 Jun 2016 14:07:03 -0700
From: Stefan Hajnoczi <stefanha@...hat.com>
To: ggarcia@...a.uab.cat
Cc: netdev@...r.kernel.org, jhansen@...are.com
Subject: Re: [RFC 1/3] vsockmon: Add tap functions.
On Sat, May 28, 2016 at 06:29:05PM +0200, ggarcia@...a.uab.cat wrote:
> From: Gerard Garcia <ggarcia@...c.uab.cat>
>
> Signed-off-by: Gerard Garcia <ggarcia@...c.uab.cat>
> ---
> include/net/af_vsock.h | 13 ++++++
> include/uapi/linux/if_arp.h | 1 +
> net/vmw_vsock/af_vsock.c | 105 ++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 119 insertions(+)
>
> diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> index 15694c9..c4593d8 100644
> --- a/include/net/af_vsock.h
> +++ b/include/net/af_vsock.h
> @@ -187,4 +187,17 @@ struct sock *vsock_find_connected_socket(struct sockaddr_vm *src,
> struct sockaddr_vm *dst);
> void vsock_for_each_connected_socket(void (*fn)(struct sock *sk));
>
> +/**** TAP ****/
> +
> +struct vsock_tap {
> + struct net_device *dev;
> + struct module *module;
> + struct list_head list;
> +};
> +
> +extern int vsock_init_tap(void);
> +extern int vsock_add_tap(struct vsock_tap *vt);
> +extern int vsock_remove_tap(struct vsock_tap *vt);
> +extern void vsock_deliver_tap(struct sk_buff *skb);
The other function prototypes in this header don't use "extern" either.
Please drop for consistency.
> +
> #endif /* __AF_VSOCK_H__ */
> diff --git a/include/uapi/linux/if_arp.h b/include/uapi/linux/if_arp.h
> index 4d024d7..869262a 100644
> --- a/include/uapi/linux/if_arp.h
> +++ b/include/uapi/linux/if_arp.h
> @@ -95,6 +95,7 @@
> #define ARPHRD_IP6GRE 823 /* GRE over IPv6 */
> #define ARPHRD_NETLINK 824 /* Netlink header */
> #define ARPHRD_6LOWPAN 825 /* IPv6 over LoWPAN */
> +#define ARPHRD_VSOCKMON 826 /* Vsock monitor header */
Previous lines use a tab character (^I) before the numeric constant.
Please follow that style for consistency.
I suggest calling it just ARPHRD_VSOCK. Netlink also uses
ARPHRD_NETLINK instead of ARPHRD_NLMON.
>
> #define ARPHRD_VOID 0xFFFF /* Void type, nothing is known */
> #define ARPHRD_NONE 0xFFFE /* zero header length */
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 6b158ab..ec7a05d 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -96,6 +96,7 @@
> #include <linux/unistd.h>
> #include <linux/wait.h>
> #include <linux/workqueue.h>
> +#include <linux/if_arp.h>
> #include <net/sock.h>
> #include <net/af_vsock.h>
>
> @@ -2012,6 +2013,110 @@ const struct vsock_transport *vsock_core_get_transport(void)
> }
> EXPORT_SYMBOL_GPL(vsock_core_get_transport);
>
> +/**** TAP ****/
Feel free to put this in a separate source file. The Kbuild can link
multiple objects into a single kernel module. That would be cleaner
than using a big comment to separate it from af_vsock.c code.
I wonder whether this tap mechanism should be generic so that netlink,
vsock, and other address families can reuse the code. This is basically
copied from netlink.
> +static DEFINE_SPINLOCK(vsock_tap_lock);
> +static struct list_head vsock_tap_all __read_mostly;
> +
> +int vsock_init_tap(void) {
> + INIT_LIST_HEAD(&vsock_tap_all);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(vsock_init_tap);
Can you use LIST_HEAD_INIT() on the vsock_tap_all declaration line to
eliminate the need for vsock_init_tap() completely?
> +
> +int vsock_add_tap(struct vsock_tap *vt) {
> + if (unlikely(vt->dev->type != ARPHRD_VSOCKMON))
> + return -EINVAL;
> +
> + spin_lock(&vsock_tap_lock);
> + list_add_rcu(&vt->list, &vsock_tap_all);
> + spin_unlock(&vsock_tap_lock);
> +
> + __module_get(vt->module);
It's slightly safer to get the module before publishing it on the list.
But in practice I guess the caller is the module so the module won't
disappear underneath us.
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(vsock_add_tap);
> +
> +int __vsock_remove_tap(struct vsock_tap *vt) {
> + bool found = false;
> + struct vsock_tap *tmp;
> +
> + spin_lock(&vsock_tap_lock);
> +
> + list_for_each_entry(tmp, &vsock_tap_all, list) {
> + if (vt == tmp) {
> + list_del_rcu(&vt->list);
> + found = true;
> + goto out;
> + }
> + }
> +
> + pr_warn("__vsock_remove_tap: %p not found\n", vt);
> +out:
> + spin_unlock(&vsock_tap_lock);
> +
> + if (found)
> + module_put(vt->module);
> +
> + return found ? 0 : -ENODEV;
> +}
> +
> +int vsock_remove_tap(struct vsock_tap *vt)
> +{
> + int ret;
> +
> + ret = __vsock_remove_tap(vt);
> + synchronize_net();
module_put() should be called after synchronize_net(). That way we
guarantee that no one is still accessing vt when the module is put. The
caller is probably the module though, so maybe there is an implicit
reference...
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(vsock_remove_tap);
> +
> +static int __vsock_deliver_tap_skb(struct sk_buff *skb,
> + struct net_device *dev)
> +{
> + struct sk_buff *vskb;
> + int ret = 0;
> +
> + if (skb) {
> + dev_hold(dev);
> + vskb = skb_clone(skb, GFP_ATOMIC);
You must handle the case where skb_clone() returns NULL. In other
words, we don't have enough memory to capture the packet and just return
-ENOMEM.
> + vskb->dev = dev;
> + vskb->pkt_type = PACKET_USER;
I'm not sure if PACKET_USER is correct (or if pkt_type matters at all).
PACKET_USER/PACKET_KERNEL seems to be purely a netlink concept to
distinguish netlink packets originating from the kernel or userspace.
AF_VSOCK is more like Ethernet where packets come from the host itself
or from a VM. I would consider PACKET_HOST and PACKET_OTHERHOST.
> + ret = dev_queue_xmit(vskb);
> + if (unlikely(ret > 0))
> + ret = net_xmit_errno(ret);
> +
> + dev_put(dev);
> + }
> +
> + return ret;
> +}
> +
> +static void __vsock_deliver_tap(struct sk_buff *skb)
> +{
> + int ret;
> + struct vsock_tap *tmp;
> +
> + list_for_each_entry_rcu(tmp, &vsock_tap_all, list) {
> + ret = __vsock_deliver_tap_skb(skb, tmp->dev);
> + if (unlikely(ret))
> + break;
> + }
> +}
> +
> +void vsock_deliver_tap(struct sk_buff *skb)
> +{
> + rcu_read_lock();
> +
> + if (unlikely(!list_empty(&vsock_tap_all)))
> + __vsock_deliver_tap(skb);
> +
> + rcu_read_unlock();
> +}
> +EXPORT_SYMBOL_GPL(vsock_deliver_tap);
> +
> MODULE_AUTHOR("VMware, Inc.");
> MODULE_DESCRIPTION("VMware Virtual Socket Family");
> MODULE_VERSION("1.0.1.0-k");
> --
> 2.8.3
>
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