From 345d3a3628b03bb9c07fdb4ac6a99714e8929dfd Mon Sep 17 00:00:00 2001
From: Asias He <asias@cloudius-systems.com>
Date: Tue, 4 Nov 2014 14:52:10 +0800
Subject: [PATCH] net: Add trim_back to packet

---
 net/packet.hh | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/net/packet.hh b/net/packet.hh
index 11c5fde6d8..7ddb139c7f 100644
--- a/net/packet.hh
+++ b/net/packet.hh
@@ -213,6 +213,7 @@ public:
     void append(packet&& p);
 
     void trim_front(size_t how_much);
+    void trim_back(size_t how_much);
 
     // get a header pointer, linearizing if necessary
     template <typename Header>
@@ -485,6 +486,23 @@ void packet::trim_front(size_t how_much) {
     }
 }
 
+inline
+void packet::trim_back(size_t how_much) {
+    assert(how_much <= _impl->_len);
+    _impl->_len -= how_much;
+    size_t i = _impl->_nr_frags - 1;
+    while (how_much && how_much >= _impl->_frags[i].size) {
+        how_much -= _impl->_frags[i--].size;
+    }
+    _impl->_nr_frags = i + 1;
+    if (how_much) {
+        _impl->_frags[i].size -= how_much;
+        if (i == 0 && _impl->using_internal_data()) {
+            _impl->_headroom += how_much;
+        }
+    }
+}
+
 template <typename Header>
 Header*
 packet::prepend_header(size_t extra_size) {