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Date: Wed, 8 Jun 2016 21:30:05 -0700
From: pravin shelar <pshelar@....org>
To: William Tu <u9012063@...il.com>
Cc: Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH] openvswitch: Add packet truncation support.
On Wed, Jun 8, 2016 at 6:18 PM, William Tu <u9012063@...il.com> wrote:
> The patch adds a new OVS action, OVS_ACTION_ATTR_TRUNC, in order to
> truncate packets. A 'max_len' is added for setting up the maximum
> packet size, and a 'cutlen' field is to record the number of bytes
> to trim the packet when the packet is outputting to a port, or when
> the packet is sent to userspace.
>
> Signed-off-by: William Tu <u9012063@...il.com>
> ---
> include/uapi/linux/openvswitch.h | 7 +++++++
> net/openvswitch/actions.c | 28 +++++++++++++++++++++++++++-
> net/openvswitch/datapath.c | 9 +++++++--
> net/openvswitch/datapath.h | 2 ++
> net/openvswitch/flow_netlink.c | 9 +++++++++
> net/openvswitch/vport.c | 1 +
> 6 files changed, 53 insertions(+), 3 deletions(-)
>
> diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
> index bb0d515..6d7ac5b 100644
> --- a/include/uapi/linux/openvswitch.h
> +++ b/include/uapi/linux/openvswitch.h
> @@ -580,6 +580,11 @@ enum ovs_userspace_attr {
>
> #define OVS_USERSPACE_ATTR_MAX (__OVS_USERSPACE_ATTR_MAX - 1)
>
> +struct ovs_action_trunc {
> + uint32_t max_len; /* Max packet size in bytes. */
This could uint16_t. as it is related to packet len.
> +};
> +#define ETH_MIN_FRAME_LEN 60
> +
There is already symbol defined, ETH_ZLEN can used here.
...
> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> index 9a3eb7a..889b78b 100644
> --- a/net/openvswitch/actions.c
> +++ b/net/openvswitch/actions.c
> @@ -750,6 +750,10 @@ static void do_output(struct datapath *dp, struct sk_buff *skb, int out_port,
>
> if (likely(vport)) {
> u16 mru = OVS_CB(skb)->mru;
> + u16 cutlen = OVS_CB(skb)->cutlen;
> +
> + if (cutlen > 0)
> + pskb_trim(skb, skb->len - cutlen);
>
> if (likely(!mru || (skb->len <= mru + ETH_HLEN))) {
> ovs_vport_send(vport, skb);
> @@ -858,10 +862,19 @@ static int sample(struct datapath *dp, struct sk_buff *skb,
> return 0;
>
> /* The only known usage of sample action is having a single user-space
> + * action, or having a truncate action followed by a single user-space
> * action. Treat this usage as a special case.
> * The output_userspace() should clone the skb to be sent to the
> * user space. This skb will be consumed by its caller.
> */
> + if (unlikely(nla_type(a) == OVS_ACTION_ATTR_TRUNC)) {
> + struct ovs_action_trunc *trunc = nla_data(a);
> +
> + OVS_CB(skb)->cutlen = skb->len > trunc->max_len ?
> + skb->len - trunc->max_len : 0;
There is no need to initialize the cutlen to zero if max-len is
greater then skb len. it should be already zero.
> + a = nla_next(a, &rem);
> + }
> +
There cutlen is set in skb cb, but next action could be other than
userspace, in that case cutlen is leaked to remain action list.
> if (likely(nla_type(a) == OVS_ACTION_ATTR_USERSPACE &&
> nla_is_last(a, rem)))
> return output_userspace(dp, skb, key, a, actions, actions_len);
> @@ -1044,13 +1057,18 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
> for (a = attr, rem = len; rem > 0;
> a = nla_next(a, &rem)) {
> int err = 0;
> + int cutlen = OVS_CB(skb)->cutlen;
>
> if (unlikely(prev_port != -1)) {
> struct sk_buff *out_skb = skb_clone(skb, GFP_ATOMIC);
>
> - if (out_skb)
> + if (out_skb) {
> + /* skb_clone does not clone the CB. */
Are you sure about this? __copy_skb_header() seem to be doing the copy.
> + OVS_CB(out_skb)->cutlen = cutlen;
> do_output(dp, out_skb, prev_port, key);
> + }
>
> + OVS_CB(skb)->cutlen = 0;
You also need to set cutlen local variable. otherwise next output
could pickup the value.
> prev_port = -1;
> }
>
> @@ -1059,6 +1077,14 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
> prev_port = nla_get_u32(a);
> break;
>
> + case OVS_ACTION_ATTR_TRUNC: {
> + struct ovs_action_trunc *trunc = nla_data(a);
> +
> + OVS_CB(skb)->cutlen = skb->len > trunc->max_len ?
> + skb->len - trunc->max_len : 0;
similar to sample() function comment, no need to set OVS_CB cutlen to zero.
> + break;
> + }
> +
> case OVS_ACTION_ATTR_USERSPACE:
> output_userspace(dp, skb, key, a, attr, len);
> break;
> diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
> index 856bd8d..fb3e5a3 100644
> --- a/net/openvswitch/datapath.c
> +++ b/net/openvswitch/datapath.c
> @@ -425,6 +425,7 @@ static int queue_userspace_packet(struct datapath *dp, struct sk_buff *skb,
> size_t len;
> unsigned int hlen;
> int err, dp_ifindex;
> + int cutlen = OVS_CB(skb)->cutlen;
>
> dp_ifindex = get_dpifindex(dp);
> if (!dp_ifindex)
> @@ -461,6 +462,9 @@ static int queue_userspace_packet(struct datapath *dp, struct sk_buff *skb,
> else
> hlen = skb->len;
>
> + if (cutlen > 0)
> + hlen -= cutlen;
> +
I do not think headline should be changed in case of sib-zero copy.
This is size of linear data in skb, changing this value could result
in wrong data copy in skb-zerocpy.
Also no need to compare cut-lea to zero, it can be directly subtracted.
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