net: always walk through filters in reverse if traffic is egress

Previously, if we attach more than one filters for a single netdev,
both ingress and egress traffic will go through net filters in same
order like:

ingress: netdev ->filter1 ->filter2 ->...filter[n] ->emulated device
egress: emulated device ->filter1 ->filter2 ->...filter[n] ->netdev.

This is against the natural feeling and will complicate filters
configuration since in some scenes, we hope filters handle the egress
traffic in a reverse order. For example, in colo-proxy (will be
implemented later), we have a redirector filter and a colo-rewriter
filter, we need the filter behave like:

ingress(->)/egress(<-): chardev<->redirector<->colo-rewriter<->emulated device

Since both buffer filter and dump do not require strict order of
filters, this patch switches to always let egress traffic walk through
net filters in reverse to simplify the possible filters configuration
in the future.

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Reviewed-by: Yang Hongyang <hongyang.yang@easystack.cn>
Signed-off-by: Jason Wang <jasowang@redhat.com>

include/net/net.h

@@ -92,7 +92,7 @@ struct NetClientState {
     NetClientDestructor *destructor;
     unsigned int queue_index;
     unsigned rxfilter_notify_enabled:1;
-    QTAILQ_HEAD(, NetFilterState) filters;
+    QTAILQ_HEAD(NetFilterHead, NetFilterState) filters;
 };
 
 typedef struct NICState {

net/filter.c

@@ -34,6 +34,22 @@ ssize_t qemu_netfilter_receive(NetFilterState *nf,
     return 0;
 }
 
+static NetFilterState *netfilter_next(NetFilterState *nf,
+                                      NetFilterDirection dir)
+{
+    NetFilterState *next;
+
+    if (dir == NET_FILTER_DIRECTION_TX) {
+        /* forward walk through filters */
+        next = QTAILQ_NEXT(nf, next);
+    } else {
+        /* reverse order */
+        next = QTAILQ_PREV(nf, NetFilterHead, next);
+    }
+
+    return next;
+}
+
 ssize_t qemu_netfilter_pass_to_next(NetClientState *sender,
                                     unsigned flags,
                                     const struct iovec *iov,
@@ -43,7 +59,7 @@ ssize_t qemu_netfilter_pass_to_next(NetClientState *sender,
     int ret = 0;
     int direction;
     NetFilterState *nf = opaque;
-    NetFilterState *next = QTAILQ_NEXT(nf, next);
+    NetFilterState *next = NULL;
 
     if (!sender || !sender->peer) {
         /* no receiver, or sender been deleted, no need to pass it further */
@@ -61,6 +77,7 @@ ssize_t qemu_netfilter_pass_to_next(NetClientState *sender,
         direction = nf->direction;
     }
 
+    next = netfilter_next(nf, direction);
     while (next) {
         /*
          * if qemu_netfilter_pass_to_next been called, means that
@@ -73,7 +90,7 @@ ssize_t qemu_netfilter_pass_to_next(NetClientState *sender,
         if (ret) {
             return ret;
         }
-        next = QTAILQ_NEXT(next, next);
+        next = netfilter_next(next, direction);
     }
 
     /*

net/net.c

@@ -580,11 +580,21 @@ static ssize_t filter_receive_iov(NetClientState *nc,
     ssize_t ret = 0;
     NetFilterState *nf = NULL;
 
-    QTAILQ_FOREACH(nf, &nc->filters, next) {
+    if (direction == NET_FILTER_DIRECTION_TX) {
-        ret = qemu_netfilter_receive(nf, direction, sender, flags, iov,
+        QTAILQ_FOREACH(nf, &nc->filters, next) {
-                                     iovcnt, sent_cb);
+            ret = qemu_netfilter_receive(nf, direction, sender, flags, iov,
-        if (ret) {
+                                         iovcnt, sent_cb);
-            return ret;
+            if (ret) {
+                return ret;
+            }
+        }
+    } else {
+        QTAILQ_FOREACH_REVERSE(nf, &nc->filters, NetFilterHead, next) {
+            ret = qemu_netfilter_receive(nf, direction, sender, flags, iov,
+                                         iovcnt, sent_cb);
+            if (ret) {
+                return ret;
+            }
         }
     }