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// -*- 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/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 {
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) {
}
};
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), m_lock("librbd::BlockGuard::m_lock") {
}
BlockGuard(const BlockGuard&) = delete;
BlockGuard &operator=(const BlockGuard&) = delete;
/**
* Detain future IO for a range of blocks. the guard will assume
* 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) {
Mutex::Locker locker(m_lock);
ldout(m_cct, 20) << "block_start=" << block_extent.block_start << ", "
<< "block_end=" << block_extent.block_end << ", "
<< "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) {
Mutex::Locker locker(m_lock);
ceph_assert(cell != nullptr);
auto &detained_block_extent = reinterpret_cast<DetainedBlockExtent &>(
*cell);
ldout(m_cct, 20) << "block_start="
<< detained_block_extent.block_extent.block_start << ", "
<< "block_end="
<< detained_block_extent.block_extent.block_end << ", "
<< "pending_ops="
<< (detained_block_extent.block_operations.empty() ?
0 : detained_block_extent.block_operations.size() - 1)
<< 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;
Mutex 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
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