1 files changed, 177 insertions, 0 deletions
diff --git a/src/librbd/BlockGuard.h b/src/librbd/BlockGuard.h
new file mode 100644
index 000000000..1e56a6eed
--- /dev/null
+++ b/src/librbd/BlockGuard.h
@@ -0,0 +1,177 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#ifndef CEPH_LIBRBD_IO_BLOCK_GUARD_H
+#define CEPH_LIBRBD_IO_BLOCK_GUARD_H
+
+#include "include/int_types.h"
+#include "common/dout.h"
+#include "common/ceph_mutex.h"
+#include <boost/intrusive/list.hpp>
+#include <boost/intrusive/set.hpp>
+#include <deque>
+#include <list>
+#include "include/ceph_assert.h"
+
+#define dout_subsys ceph_subsys_rbd
+#undef dout_prefix
+#define dout_prefix *_dout << "librbd::BlockGuard: " << this << " " \
+                           <<  __func__ << ": "
+
+namespace librbd {
+
+struct BlockExtent {
+  // [block_start, block_end)
+  uint64_t block_start = 0;
+  uint64_t block_end = 0;
+
+  BlockExtent() {
+  }
+  BlockExtent(uint64_t block_start, uint64_t block_end)
+    : block_start(block_start), block_end(block_end) {
+  }
+
+  friend std::ostream& operator<< (std::ostream& os, const BlockExtent& block_extent) {
+    os << "[block_start=" << block_extent.block_start
+       << ", block_end=" << block_extent.block_end << "]";
+    return os;
+  }
+};
+
+struct BlockGuardCell {
+};
+
+/**
+ * Helper class to restrict and order concurrent IO to the same block. The
+ * definition of a block is dependent upon the user of this class. It might
+ * represent a backing object, 512 byte sectors, etc.
+ */
+template <typename BlockOperation>
+class BlockGuard {
+private:
+  struct DetainedBlockExtent;
+
+public:
+  typedef std::list<BlockOperation> BlockOperations;
+
+  BlockGuard(CephContext *cct)
+    : m_cct(cct) {
+  }
+
+  BlockGuard(const BlockGuard&) = delete;
+  BlockGuard &operator=(const BlockGuard&) = delete;
+
+  /**
+   * Detain future IO for a range of blocks. the guard will keep
+   * ownership of the provided operation if the operation is blocked.
+   * @return 0 upon success and IO can be issued
+   *         >0 if the IO is blocked,
+   *         <0 upon error
+   */
+  int detain(const BlockExtent &block_extent, BlockOperation *block_operation,
+             BlockGuardCell **cell) {
+    std::lock_guard locker{m_lock};
+    ldout(m_cct, 20) << block_extent
+                     << ", free_slots="
+                     << m_free_detained_block_extents.size()
+                     << dendl;
+
+    DetainedBlockExtent *detained_block_extent;
+    auto it = m_detained_block_extents.find(block_extent);
+    if (it != m_detained_block_extents.end()) {
+      // request against an already detained block
+      detained_block_extent = &(*it);
+      if (block_operation != nullptr) {
+        detained_block_extent->block_operations.emplace_back(
+          std::move(*block_operation));
+      }
+
+      // alert the caller that the IO was detained
+      *cell = nullptr;
+      return detained_block_extent->block_operations.size();
+    } else {
+      if (!m_free_detained_block_extents.empty()) {
+        detained_block_extent = &m_free_detained_block_extents.front();
+        detained_block_extent->block_operations.clear();
+        m_free_detained_block_extents.pop_front();
+      } else {
+        ldout(m_cct, 20) << "no free detained block cells" << dendl;
+        m_detained_block_extent_pool.emplace_back();
+        detained_block_extent = &m_detained_block_extent_pool.back();
+      }
+
+      detained_block_extent->block_extent = block_extent;
+      m_detained_block_extents.insert(*detained_block_extent);
+      *cell = reinterpret_cast<BlockGuardCell*>(detained_block_extent);
+      return 0;
+    }
+  }
+
+  /**
+   * Release any detained IO operations from the provided cell.
+   */
+  void release(BlockGuardCell *cell, BlockOperations *block_operations) {
+    std::lock_guard locker{m_lock};
+
+    ceph_assert(cell != nullptr);
+    auto &detained_block_extent = reinterpret_cast<DetainedBlockExtent &>(
+      *cell);
+    ldout(m_cct, 20) << detained_block_extent.block_extent
+                     << ", pending_ops="
+                     << detained_block_extent.block_operations.size()
+                     << dendl;
+
+    *block_operations = std::move(detained_block_extent.block_operations);
+    m_detained_block_extents.erase(detained_block_extent.block_extent);
+    m_free_detained_block_extents.push_back(detained_block_extent);
+  }
+
+private:
+  struct DetainedBlockExtent : public boost::intrusive::list_base_hook<>,
+                               public boost::intrusive::set_base_hook<> {
+    BlockExtent block_extent;
+    BlockOperations block_operations;
+  };
+
+  struct DetainedBlockExtentKey {
+    typedef BlockExtent type;
+    const BlockExtent &operator()(const DetainedBlockExtent &value) {
+      return value.block_extent;
+    }
+  };
+
+  struct DetainedBlockExtentCompare {
+    bool operator()(const BlockExtent &lhs,
+                    const BlockExtent &rhs) const {
+      // check for range overlap (lhs < rhs)
+      if (lhs.block_end <= rhs.block_start) {
+        return true;
+      }
+      return false;
+    }
+  };
+
+  typedef std::deque<DetainedBlockExtent> DetainedBlockExtentsPool;
+  typedef boost::intrusive::list<DetainedBlockExtent> DetainedBlockExtents;
+  typedef boost::intrusive::set<
+    DetainedBlockExtent,
+    boost::intrusive::compare<DetainedBlockExtentCompare>,
+    boost::intrusive::key_of_value<DetainedBlockExtentKey> >
+      BlockExtentToDetainedBlockExtents;
+
+  CephContext *m_cct;
+
+  ceph::mutex m_lock = ceph::make_mutex("librbd::BlockGuard::m_lock");
+  DetainedBlockExtentsPool m_detained_block_extent_pool;
+  DetainedBlockExtents m_free_detained_block_extents;
+  BlockExtentToDetainedBlockExtents m_detained_block_extents;
+
+};
+
+} // namespace librbd
+
+#undef dout_subsys
+#undef dout_prefix
+#define dout_prefix *_dout
+
+#endif // CEPH_LIBRBD_IO_BLOCK_GUARD_H