From ae1122bfc8b15632d576f61e647c8e4cf326583b Mon Sep 17 00:00:00 2001
From: Glauber Costa <glommer@cloudius-systems.com>
Date: Wed, 5 Nov 2014 22:34:04 +0100
Subject: [PATCH] xen: manage index list

Aside from managing the grant references, we also need to manage the positional
indexes in the array. We need to keep track of which indexes are free, and
which are used. Because we need the actual position number to fill xen's data
structures, I figured we could use a queue and then fill it up with all the
integers in our range. The queue is already futurized, so that's easy.

Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
---
 net/xenfront.cc | 13 ++++++++-----
 net/xenfront.hh | 13 ++++++++++---
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/net/xenfront.cc b/net/xenfront.cc
index c2f0563876..f2a3bea12f 100644
--- a/net/xenfront.cc
+++ b/net/xenfront.cc
@@ -111,7 +111,7 @@ xenfront_net_device::send(packet _p) {
     // FIXME: negotiate and use scatter/gather
     _p.linearize();
 
-    return _tx_ring.free_idx().then([this, p = std::move(_p), frag] (uint32_t idx) mutable {
+    return _tx_ring.entries.get_index().then([this, p = std::move(_p), frag] (unsigned idx) mutable {
 
         auto req_prod = _tx_ring._sring->req_prod;
 
@@ -152,11 +152,14 @@ xenfront_net_device::send(packet _p) {
 #define rmb() asm volatile("lfence":::"memory");
 #define wmb() asm volatile("":::"memory");
 
-// FIXME: This is totally wrong, just coded so we can gt started with sending
 template <typename T>
-future<uint32_t> front_ring<T>::free_idx() {
-    static uint32_t idx = 0;
-    return make_ready_future<uint32_t>(idx++);
+future<unsigned> front_ring<T>::entries::get_index() {
+    return _ids.pop_eventually();
+}
+
+template <typename T>
+future<> front_ring<T>::entries::free_index(unsigned id) {
+    return _ids.push_eventually(std::move(id));
 }
 
 future<> xenfront_net_device::queue_rx_packet() {
diff --git a/net/xenfront.hh b/net/xenfront.hh
index f43a944f95..04ebb1681c 100644
--- a/net/xenfront.hh
+++ b/net/xenfront.hh
@@ -9,6 +9,7 @@
 #include "net.hh"
 #include "core/sstring.hh"
 #include "core/xen/gntalloc.hh"
+#include "core/queue.hh"
 
 std::unique_ptr<net::device> create_xenfront_net_device(boost::program_options::variables_map opts, bool userspace);
 boost::program_options::options_description get_xenfront_net_options_description();
@@ -71,13 +72,21 @@ template <typename T>
 class front_ring {
 public:
     class entries {
+    protected:
+        queue<unsigned> _ids;
     private:
         std::array<gntref, front_ring<T>::nr_ents> _entries;
         front_ring<T> *_ring;
     public:
-        entries(front_ring<T> *ring) : _ring(ring) {}
+        entries(front_ring<T> *ring) : _ids(front_ring<T>::nr_ents), _ring(ring) {
+            for (unsigned i = 0; i < front_ring<T>::nr_ents; ++i) {
+                _ids.push(std::move(i));
+            }
+        }
         gntref& operator[](std::size_t i) { return _entries[_ring->idx(i)]; }
         friend front_ring;
+        future<unsigned> get_index();
+        future<> free_index(unsigned index);
     };
 protected:
     uint32_t idx(int i) { return i & (nr_ents - 1); }
@@ -92,8 +101,6 @@ public:
         , _sring(new (r.page) sring<T>()) {
     }
 
-
-    future<uint32_t> free_idx();
     entries entries;
 
     sring<T> *_sring;