// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

#include <RB_INC_FCNTL_H
#include "db.h"

//
// env::env
//

ircd::db::database::env::env(database *const &d)
:d{*d},
st{std::make_unique<state>(d)}
{
}

ircd::db::database::env::~env()
noexcept
{
}

rocksdb::Status
ircd::db::database::env::NewSequentialFile(const std::string &name,
                                           std::unique_ptr<SequentialFile> *const r,
                                           const EnvOptions &options)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': new sequential file '%s' options:%p [mm:%b direct:%b bufsz:%zu readahead:%zu]",
		d.name,
		name,
		&options,
		options.use_mmap_reads,
		options.use_direct_reads,
		options.random_access_max_buffer_size,
		options.compaction_readahead_size,
	};
	#endif

	*r = std::make_unique<sequential_file>(&d, name, options);
	return Status::OK();
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::NewRandomAccessFile(const std::string &name,
                                             std::unique_ptr<RandomAccessFile> *const r,
                                             const EnvOptions &options)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': new random access file '%s' options:%p [mm:%b direct:%b bufsz:%zu readahead:%zu]",
		d.name,
		name,
		&options,
		options.use_mmap_reads,
		options.use_direct_reads,
		options.random_access_max_buffer_size,
		options.compaction_readahead_size,
	};
	#endif

	*r = std::make_unique<random_access_file>(&d, name, options);
	return Status::OK();
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::NewWritableFile(const std::string &name,
                                         std::unique_ptr<WritableFile> *const r,
                                         const EnvOptions &options)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': new writable file '%s' options:%p [mm:%b direct:%b rl:%p bufsz:%zu syncsz:%zu]",
		d.name,
		name,
		&options,
		options.use_mmap_writes,
		options.use_direct_writes,
		options.rate_limiter,
		options.writable_file_max_buffer_size,
		options.bytes_per_sync,
	};
	#endif

	if(options.use_direct_writes)
		*r = std::make_unique<writable_file_direct>(&d, name, options, true);
	else
		*r = std::make_unique<writable_file>(&d, name, options, true);

	return Status::OK();
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::ReopenWritableFile(const std::string &name,
                                            std::unique_ptr<WritableFile> *const r,
                                            const EnvOptions &options)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': reopen writable file '%s' options:%p",
		d.name,
		name,
		&options
	};
	#endif

	if(options.use_direct_writes)
		*r = std::make_unique<writable_file_direct>(&d, name, options, false);
	else
		*r = std::make_unique<writable_file>(&d, name, options, false);

	return Status::OK();
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
__attribute__((unused))
ircd::db::database::env::ReuseWritableFile(const std::string &name,
                                           const std::string &old_name,
                                           std::unique_ptr<WritableFile> *const r,
                                           const EnvOptions &options)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': reuse writable file '%s' old '%s' options:%p",
		d.name,
		name,
		old_name,
		&options
	};
	#endif

	throw ircd::not_implemented
	{
		"'%s': ReuseWritableFile(name:'%s' old:'%s')",
		d.name,
		name,
		old_name
	};

	return Status::OK();
	//return defaults.ReuseWritableFile(name, old_name, r, options);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::NewRandomRWFile(const std::string &name,
                                         std::unique_ptr<RandomRWFile> *const result,
                                         const EnvOptions &options)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': new random read/write file '%s' options:%p",
		d.name,
		name,
		&options
	};
	#endif

	*result = std::make_unique<random_rw_file>(&d, name, options);
	return Status::OK();
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::NewDirectory(const std::string &name,
                                      std::unique_ptr<Directory> *const result)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': new directory '%s'",
		d.name,
		name
	};
	#endif

	std::unique_ptr<Directory> defaults;
	const auto ret
	{
		this->defaults.NewDirectory(name, &defaults)
	};

	*result = std::make_unique<directory>(&d, name, std::move(defaults));
	return ret;
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::FileExists(const std::string &f)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': file exists '%s'",
		d.name,
		f
	};
	#endif

	return defaults.FileExists(f);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::GetChildren(const std::string &dir,
                                     std::vector<std::string> *const r)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': get children of directory '%s'",
		d.name,
		dir
	};
	#endif

	return defaults.GetChildren(dir, r);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::GetChildrenFileAttributes(const std::string &dir,
                                                   std::vector<FileAttributes> *const result)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': get children file attributes of directory '%s'",
		d.name,
		dir
	};
	#endif

	return defaults.GetChildrenFileAttributes(dir, result);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::DeleteFile(const std::string &name)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': delete file '%s'",
		d.name,
		name
	};
	#endif

	return defaults.DeleteFile(name);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::CreateDir(const std::string &name)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': create directory '%s'",
		d.name,
		name
	};
	#endif

	return defaults.CreateDir(name);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::CreateDirIfMissing(const std::string &name)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': create directory if missing '%s'",
		d.name,
		name
	};
	#endif

	return defaults.CreateDirIfMissing(name);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::DeleteDir(const std::string &name)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': delete directory '%s'",
		d.name,
		name
	};
	#endif

	return defaults.DeleteDir(name);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::GetFileSize(const std::string &name,
                                     uint64_t *const s)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': get file size '%s'",
		d.name,
		name
	};
	#endif

	assert(s);
	*s = fs::size(name);
	return Status::OK();
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::GetFileModificationTime(const std::string &name,
                                                 uint64_t *const file_mtime)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': get file mtime '%s'",
		d.name,
		name
	};
	#endif

	return defaults.GetFileModificationTime(name, file_mtime);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::RenameFile(const std::string &s,
                                    const std::string &t)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': rename file '%s' to '%s'",
		d.name,
		s,
		t
	};
	#endif

	return defaults.RenameFile(s, t);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::LinkFile(const std::string &s,
                                  const std::string &t)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': link file '%s' to '%s'",
		d.name,
		s,
		t
	};
	#endif

	return defaults.LinkFile(s, t);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::LockFile(const std::string &name,
                                  FileLock** l)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': lock file '%s'",
		d.name,
		name
	};
	#endif

	return defaults.LockFile(name, l);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::UnlockFile(FileLock *const l)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': unlock file lock:%p",
		d.name,
		l
	};
	#endif

	return defaults.UnlockFile(l);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::GetTestDirectory(std::string *const path)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	return defaults.GetTestDirectory(path);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::GetAbsolutePath(const std::string &db_path,
                                         std::string *const output_path)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': get absolute path from '%s' ret:%p",
		d.name,
		db_path,
		output_path
	};
	#endif

	return defaults.GetAbsolutePath(db_path, output_path);
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::NewLogger(const std::string &name,
                                   std::shared_ptr<Logger> *const result)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': new logger '%s' result:%p",
		d.name,
		name,
		(const void *)result
	};
	#endif

	return defaults.NewLogger(name, result);
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::GetHostName(char *const name,
                                     uint64_t len)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': get host name name:%p len:%lu",
		d.name,
		name,
		len
	};
	#endif

	return defaults.GetHostName(name, len);
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

uint64_t
ircd::db::database::env::NowMicros()
noexcept try
{
	return defaults.NowMicros();
}
catch(const std::exception &e)
{
	throw panic
	{
		"'%s': now micros :%s",
		d.name,
		e.what()
	};
}

rocksdb::Status
ircd::db::database::env::GetCurrentTime(int64_t *const unix_time)
noexcept try
{
	return defaults.GetCurrentTime(unix_time);
}
catch(const std::exception &e)
{
	return error_to_status{e};
}

std::string
ircd::db::database::env::TimeToString(uint64_t time)
noexcept try
{
	return defaults.TimeToString(time);
}
catch(const std::exception &e)
{
	throw panic
	{
		"'%s': time to string :%s",
		d.name,
		e.what()
	};
}

void
ircd::db::database::env::SleepForMicroseconds(int micros)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		"'%s': sleep for %d microseconds",
		d.name,
		micros
	};
	#endif

	ctx::sleep(microseconds(micros));
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': sleep micros:%d :%s",
		d.name,
		micros,
		e.what()
	};
}

void
ircd::db::database::env::Schedule(void (*f)(void* arg),
                                  void *const a,
                                  Priority prio,
                                  void *const tag,
                                  void (*u)(void* arg))
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': schedule func:%p a:%p tag:%p u:%p prio:%s",
		d.name,
		f,
		a,
		tag,
		u,
		reflect(prio)
	};
	#endif

	assert(st);
	auto &pool
	{
		*st->pool.at(prio)
	};

	pool(state::task
	{
		f, u, a
	});
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': schedule func:%p a:%p tag:%p u:%p prio:%s",
		d.name,
		f,
		a,
		tag,
		u,
		reflect(prio)
	};
}

int
ircd::db::database::env::UnSchedule(void *const tag,
                                    const Priority prio)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': unschedule tag:%p prio:%s",
		d.name,
		tag,
		reflect(prio)
	};
	#endif

	assert(st);
	auto &pool
	{
		*st->pool.at(prio)
	};

	return pool.cancel(tag);
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': unschedule tag:%p prio:%s :%s",
		d.name,
		tag,
		reflect(prio),
		e.what()
	};

	return 0;
}

void
ircd::db::database::env::StartThread(void (*f)(void*),
                                     void *const a)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': start thread func:%p a:%p",
		d.name,
		f,
		a
	};
	#endif

	throw ircd::not_implemented
	{
		"Independent (non-pool) context spawning not yet implemented"
	};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': start thread :%s",
		d.name,
		e.what()
	};
}

void
ircd::db::database::env::WaitForJoin()
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wait for all ctx to join",
		d.name
	};
	#endif

	assert(st);
	for(auto &pool : st->pool)
		if(pool)
			pool->join();
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': wait for join :%s",
		d.name,
		e.what()
	};
}

unsigned int
ircd::db::database::env::GetThreadPoolQueueLen(Priority prio)
const noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': get thread pool queue len prio:%s",
		d.name,
		reflect(prio)
	};
	#endif

	assert(st);
	const auto &pool
	{
		*st->pool.at(prio)
	};

	return pool.tasks.size();
}
catch(const std::exception &e)
{
	throw panic
	{
		"'%s': set background threads :%s",
		d.name,
		e.what()
	};
}

void
ircd::db::database::env::SetBackgroundThreads(int num,
                                              Priority prio)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': set background threads prio:%s num:%d",
		d.name,
		reflect(prio),
		num
	};
	#endif

	assert(st);
	auto &pool
	{
		*st->pool.at(prio)
	};

	pool.p.set(num);
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': set background threads prio:%s num:%d :%s",
		d.name,
		reflect(prio),
		num,
		e.what()
	};
}

void
ircd::db::database::env::IncBackgroundThreadsIfNeeded(int num,
                                                      Priority prio)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': increase background threads num:%d prio:%s",
		d.name,
		num,
		reflect(prio)
	};
	#endif

	assert(st);
	auto &pool
	{
		*st->pool.at(prio)
	};

	pool.p.add(num);
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': inc background threads num:%d prio:%s :%s",
		d.name,
		num,
		reflect(prio),
		e.what()
	};
}

void
ircd::db::database::env::LowerThreadPoolIOPriority(Priority prio)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': lower thread pool priority prio:%s",
		d.name,
		reflect(prio)
	};
	#endif

	assert(st);
	auto &pool
	{
		*st->pool.at(prio)
	};

	switch(pool.iopri)
	{
		case IOPriority::IO_HIGH:
			pool.iopri = IOPriority::IO_LOW;
			break;

		default:
			break;
	}
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': lower thread pool IO priority pool:%s :%s",
		d.name,
		reflect(prio),
		e.what()
	};
}

rocksdb::Status
ircd::db::database::env::GetThreadList(std::vector<ThreadStatus> *const list)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': get thread list %p (%zu)",
		d.name,
		list,
		list? list->size() : 0UL
	};
	#endif

	throw ircd::not_implemented
	{
		"'%s': GetThreadList()", d.name
	};

	return defaults.GetThreadList(list);
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': get thread list:%p :%s",
		d.name,
		list,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::ThreadStatusUpdater *
ircd::db::database::env::GetThreadStatusUpdater()
const noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': get thread status updater",
		d.name,
	};
	#endif

	return defaults.GetThreadStatusUpdater();
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': get thread status updater :%s",
		d.name,
		e.what()
	};

	return nullptr;
}


uint64_t
ircd::db::database::env::GetThreadID()
const noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': get thread ID",
		d.name,
	};
	#endif

	return ctx::this_ctx::id();
}
catch(const std::exception &e)
{
	throw panic
	{
		"'%s': get thread id :%s",
		d.name,
		e.what()
	};
}

int
ircd::db::database::env::GetBackgroundThreads(Priority prio)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': get background threads prio:%s",
		d.name,
		reflect(prio)
	};
	#endif

	assert(st);
	const auto &pool
	{
		*st->pool.at(prio)
	};

	return pool.p.size();
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': get background threads prio:%s :%s",
		d.name,
		reflect(prio),
		e.what()
	};

	return 0;
}

//
// writable_file
//

ircd::db::database::env::writable_file::writable_file(database *const &d,
                                                      const std::string &name,
                                                      const EnvOptions &env_opts,
                                                      const bool &trunc)
try
:d
{
	*d
}
,env_opts
{
	env_opts
}
,opts{[this, &trunc]
{
	fs::fd::opts ret
	{
		std::ios::out |
		(trunc? std::ios::trunc : std::ios::openmode(0))
	};

	ret.direct = this->env_opts.use_direct_writes;
	ret.cloexec = this->env_opts.set_fd_cloexec;
	return ret;
}()}
,fd
{
	name, this->opts
}
,preallocation_block_size
{
	ircd::info::page_size
}
{
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': opened wfile:%p fd:%d '%s'",
		d->name,
		this,
		int(fd),
		name
	};
	#endif

	// Workaround a RocksDB bug which doesn't propagate EnvOptions properly
	// on some constructions of WritableFile early on during db open. We'll
	// get an env_opts.allow_fallocate==true here while it should be false
	// from the DBOptions at d->opts. We use &= so it's not set to true when
	// the caller specifically wants it false just for them.
	assert(d && d->opts);
	this->env_opts.allow_fallocate &= d->opts->allow_fallocate;
	//assert(env_opts.allow_fallocate == d->opts->allow_fallocate);
}
catch(const std::exception &e)
{
	log::error
	{
		log, "'%s': opening wfile:%p `%s' :%s",
		d->name,
		this,
		name,
		e.what()
	};
}

ircd::db::database::env::writable_file::~writable_file()
noexcept
{
	Close();

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': closed wfile:%p fd:%d",
		d.name,
		this,
		int(fd)
	};
	#endif
}

rocksdb::Status
ircd::db::database::env::writable_file::Close()
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	if(!fd)
		return Status::OK();

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p fd:%d close",
		d.name,
		this,
		int(fd)
	};
	#endif

	fd = fs::fd{};
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p close :%s",
		d.name,
		this,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::error
	{
		log, "'%s': wfile:%p close :%s",
		d.name,
		this,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::writable_file::Flush()
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p fd:%d flush",
		d.name,
		this,
		int(fd),
	};
	#endif

	fs::sync_opts opts;
	opts.metadata = false;
	fs::flush(fd, opts);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p fd:%d flush :%s",
		d.name,
		this,
		int(fd),
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::error
	{
		log, "'%s': wfile:%p fd:%d flush :%s",
		d.name,
		this,
		int(fd),
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::writable_file::Sync()
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p sync",
		d.name,
		this
	};
	#endif

	fs::sync_opts opts;
	fs::sync(fd, opts);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p sync :%s",
		d.name,
		this,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::error
	{
		log, "'%s': wfile:%p sync :%s",
		d.name,
		this,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::writable_file::Fsync()
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p fsync",
		d.name,
		this
	};
	#endif

	fs::sync_opts opts;
	fs::flush(fd, opts);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p fsync :%s",
		d.name,
		this,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::error
	{
		log, "'%s': wfile:%p fsync :%s",
		d.name,
		this,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::writable_file::RangeSync(uint64_t offset,
                                                  uint64_t length)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		"'%s': wfile:%p fd:%d range sync offset:%lu length:%lu",
		d.name,
		this,
		int(fd),
		offset,
		length
	};
	#endif

	// RocksDB sez they want us to initiate flushing of dirty pages
	// asynchronously without waiting for completion. RocksDB allows
	// this callback to be a no-op and do nothing at all.
	//
	// We plug this into a "range flush" gimmick in ircd::fs which almost
	// certainly calls fdatasync() and ignores the range; it may one day
	// on supporting platforms and in certain circumstances call
	// sync_file_range() without any of the wait flags and respect the range.

	fs::sync_opts opts;
	opts.metadata = false;
	fs::flush(fd, offset, length, opts);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p fd:%d range sync offset:%zu length:%zu :%s",
		d.name,
		this,
		int(fd),
		offset,
		length,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': wfile:%p fd:%d range sync offset:%zu length:%zu :%s",
		d.name,
		this,
		int(fd),
		offset,
		length,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::writable_file::Truncate(uint64_t size)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		"'%s': wfile:%p fd:%d truncate to %lu bytes",
		d.name,
		this,
		int(fd),
		size
	};
	#endif

	fs::write_opts wopts;
	wopts.priority = this->prio_val;
	wopts.nodelay = this->nodelay;
	fs::truncate(fd, size, wopts);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p fd:%d truncate to %lu bytes :%s",
		d.name,
		this,
		int(fd),
		size,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': wfile:%p fd:%d truncate to %lu bytes :%s",
		d.name,
		this,
		int(fd),
		size,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::writable_file::InvalidateCache(size_t offset,
                                                        size_t length)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p fd:%d invalidate cache offset:%zu length:%zu",
		d.name,
		this,
		int(fd),
		offset,
		length
	};
	#endif

	if(opts.direct)
		return Status::OK();

	fs::evict(fd, length, offset);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p fd:%d invalidate cache offset:%zu length:%zu",
		d.name,
		this,
		int(fd),
		offset,
		length
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': wfile:%p fd:%d invalidate cache offset:%zu length:%zu",
		d.name,
		this,
		int(fd),
		offset,
		length
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::writable_file::Append(const Slice &s)
noexcept try
{
	assert(!opts.direct);
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p fd:%d append:%p bytes:%zu",
		d.name,
		this,
		int(fd),
		data(s),
		size(s),
	};
	#endif

	fs::write_opts wopts;
	wopts.priority = this->prio_val;
	wopts.nodelay = this->nodelay;
	const const_buffer buf
	{
		data(s), size(s)
	};

	fs::append(fd, buf, wopts);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p fd:%d append:%p size:%zu :%s",
		d.name,
		this,
		int(fd),
		data(s),
		size(s),
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': wfile:%p fd:%d append:%p size:%zu :%s",
		d.name,
		this,
		int(fd),
		data(s),
		size(s),
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::writable_file::PositionedAppend(const Slice &s,
                                                         uint64_t offset)
noexcept try
{
	assert(!opts.direct);
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		"'%s': wfile:%p fd:%d append:%p bytes:%zu offset:%lu",
		d.name,
		this,
		int(fd),
		data(s),
		size(s),
		offset
	};
	#endif

	fs::write_opts wopts;
	wopts.priority = this->prio_val;
	wopts.nodelay = this->nodelay;
	wopts.offset = offset;
	const const_buffer buf
	{
		data(s), size(s)
	};

	fs::append(fd, buf, wopts);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p fd:%d append:%p size:%zu offset:%zu :%s",
		d.name,
		this,
		int(fd),
		data(s),
		size(s),
		offset,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': wfile:%p fd:%d append:%p size:%zu offset:%lu :%s",
		d.name,
		this,
		int(fd),
		data(s),
		size(s),
		offset,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::writable_file::Allocate(uint64_t offset,
                                                 uint64_t length)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p fd:%d allocate offset:%lu length:%lu%s%s",
		d.name,
		this,
		int(fd),
		offset,
		length,
		env_opts.fallocate_with_keep_size? " KEEP_SIZE" : "",
		env_opts.allow_fallocate? "" : " (DISABLED)"
	};
	#endif

	if(!env_opts.allow_fallocate)
		return Status::NotSupported();

	_allocate(offset, length);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p fd:%d allocate offset:%zu length:%zu :%s",
		d.name,
		this,
		int(fd),
		offset,
		length,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': wfile:%p fd:%d allocate offset:%zu length:%zu :%s",
		d.name,
		this,
		int(fd),
		offset,
		length,
		e.what()
	};

	return error_to_status{e};
}

void
ircd::db::database::env::writable_file::PrepareWrite(size_t offset,
                                                     size_t length)
noexcept
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p prepare write offset:%zu length:%zu",
		d.name,
		this,
		offset,
		length
	};
	#endif

	if(!env_opts.allow_fallocate)
		return;

	_allocate(offset, length);
}

void
ircd::db::database::env::writable_file::_allocate(const size_t &offset,
                                                  const size_t &length)
{
	const size_t first_block
	{
		offset / preallocation_block_size
	};

	const size_t last_block
	{
		(offset + length) / preallocation_block_size
	};

	const ssize_t missing_blocks
	{
		ssize_t(last_block) - preallocation_last_block
	};

	// Fast bail when the offset and length are behind the last block already
	// allocated. We don't support windowing here. If this branch is not taken
	// we'll fallocate() contiguously from the last fallocate() (or offset 0).
	if(missing_blocks <= 0)
		return;

	const ssize_t start_block
	{
		preallocation_last_block + 1
	};

	const size_t allocate_offset
	{
		start_block * preallocation_block_size
	};

	const size_t allocate_length
	{
		missing_blocks * preallocation_block_size
	};

	fs::write_opts wopts;
	wopts.offset = allocate_offset;
	wopts.priority = this->prio_val;
	wopts.nodelay = this->nodelay;
	wopts.keep_size = env_opts.fallocate_with_keep_size;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p fd:%d allocating %zd blocks after block:%zu offset:%lu length:%lu%s",
		d.name,
		this,
		int(fd),
		missing_blocks,
		start_block,
		allocate_offset,
		allocate_length,
		wopts.keep_size? " KEEP_SIZE" : ""
	};
	#endif

	assert(env_opts.allow_fallocate);
	assert(bool(d.opts));
	assert(d.opts->allow_fallocate);

	fs::allocate(fd, allocate_length, wopts);
	this->preallocation_last_block = last_block;
}

void
ircd::db::database::env::writable_file::GetPreallocationStatus(size_t *const block_size,
                                                               size_t *const last_allocated_block)
noexcept
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	*block_size = this->preallocation_block_size;
	*last_allocated_block = this->preallocation_last_block;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p get preallocation block_size(%p):%zu last_block(%p):%zu",
		d.name,
		this,
		block_size,
		*block_size,
		last_allocated_block,
		*last_allocated_block
	};
	#endif
}

void
ircd::db::database::env::writable_file::SetPreallocationBlockSize(size_t size)
noexcept
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p set preallocation block size:%zu",
		d.name,
		this,
		size
	};
	#endif

	this->preallocation_block_size = size;
}

uint64_t
ircd::db::database::env::writable_file::GetFileSize()
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p fd:%d get file size",
		d.name,
		this,
		int(fd)
	};
	#endif

	return fs::size(fd);
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': wfile:%p fd:%d get file size :%s",
		d.name,
		this,
		int(fd),
		e.what()
	};

	return 0;
}

void
ircd::db::database::env::writable_file::SetIOPriority(Env::IOPriority prio)
noexcept
{
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p IO priority %s",
		d.name,
		this,
		reflect(prio)
	};
	#endif

	this->prio = prio;
	switch(this->prio)
	{
		case IOPriority::IO_HIGH:
			prio_val = -5; //TODO: magic
			nodelay = true;
			break;

		default:
		case IOPriority::IO_LOW:
			prio_val = 5; //TODO: magic
			nodelay = false;
			break;
	}
}

rocksdb::Env::IOPriority
ircd::db::database::env::writable_file::GetIOPriority()
noexcept
{
	return prio;
}

void
ircd::db::database::env::writable_file::SetWriteLifeTimeHint(WriteLifeTimeHint hint)
noexcept try
{
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p hint:%d %s",
		d.name,
		this,
		int(hint),
		reflect(hint),
	};
	#endif

	this->hint = hint;
	fs::write_life(fd, this->hint);
}
catch(const std::system_error &e)
{
	log::derror
	{
		log, "'%s': wfile:%p fd:%d setting write lifetime hint:%d %s :%s",
		d.name,
		this,
		int(fd),
		int(hint),
		reflect(hint),
		e.what(),
	};
}

rocksdb::Env::WriteLifeTimeHint
ircd::db::database::env::writable_file::GetWriteLifeTimeHint()
noexcept
{
	return hint;
}

size_t
ircd::db::database::env::writable_file::GetUniqueId(char *const id,
                                                    size_t max_size)
const noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		"'%s': wfile:%p get unique id:%p max_size:%zu",
		d.name,
		this,
		id,
		max_size
	};
	#endif

	const mutable_buffer buf
	{
		id, max_size
	};

	//return size(fs::uuid(fd, buf));
	return 0;
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': wfile:%p get unique id :%s",
		d.name,
		this,
		e.what()
	};

	return 0;
}

bool
ircd::db::database::env::writable_file::IsSyncThreadSafe()
const noexcept try
{
	return true;
}
catch(...)
{
	return false;
}

//
// writable_file_direct
//

ircd::db::database::env::writable_file_direct::writable_file_direct(database *const &d,
                                                                    const std::string &name,
                                                                    const EnvOptions &env_opts,
                                                                    const bool &trunc)
:writable_file
{
	d, name, env_opts, trunc
}
,alignment
{
	fs::block_size(fd)
}
,logical_offset
{
	!trunc?
		fs::size(fd):
		size_t(0)
}
,buffer
{
	alignment, alignment
}
{
	zero(buffer);
	if(!aligned(logical_offset))
		throw panic
		{
			"direct writable file requires read into buffer."
		};
}

rocksdb::Status
ircd::db::database::env::writable_file_direct::Close()
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	if(!fd)
		return Status::OK();

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p DIRECT fd:%d close",
		d.name,
		this,
		int(fd)
	};
	#endif

	if(logical_offset > 0 && fs::size(fd) != logical_offset)
	{
		fs::write_opts wopts;
		wopts.priority = this->prio_val;
		wopts.nodelay = true;
		fs::truncate(fd, logical_offset, wopts);
	}

	fd = fs::fd{};
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p DIRECT close :%s",
		d.name,
		this,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::error
	{
		log, "'%s': wfile:%p DIRECT close :%s",
		d.name,
		this,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::writable_file_direct::Truncate(uint64_t size)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		"'%s': wfile:%p DIRECT fd:%d truncate to %lu bytes",
		d.name,
		this,
		int(fd),
		size
	};
	#endif

	fs::write_opts wopts;
	wopts.priority = this->prio_val;
	wopts.nodelay = true;
	fs::truncate(fd, size, wopts);
	logical_offset = size;
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p DIRECT fd:%d truncate to %lu bytes :%s",
		d.name,
		this,
		int(fd),
		size,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': wfile:%p DIRECT fd:%d truncate to %lu bytes :%s",
		d.name,
		this,
		int(fd),
		size,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::writable_file_direct::Append(const Slice &s)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	if(!aligned(logical_offset) || !aligned(data(s)))
		log::dwarning
		{
			log, "'%s': ALIGNMENT CHECK fd:%d append:%p%s bytes:%zu%s logical_offset:%zu%s",
			d.name,
			int(fd),
			data(s),
			aligned(data(s))? "" : "#AC",
			size(s),
			aligned(size(s))? "" : "#AC",
			logical_offset,
			aligned(logical_offset)? "" : "#AC"
		};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p DIRECT fd:%d append:%p%s bytes:%zu%s logical_offset:%zu%s",
		d.name,
		this,
		int(fd),
		data(s),
		aligned(data(s))? "" : "#AC",
		size(s),
		aligned(size(s))? "" : "#AC",
		logical_offset,
		aligned(logical_offset)? "" : "#AC"
	};
	#endif

	const auto logical_check
	{
		logical_offset
	};

	const_buffer buf
	{
		slice(s)
	};

	while(!empty(buf))
		buf = write(buf);

	assert(logical_check + size(slice(s)) == logical_offset);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': wfile:%p DIRECT fd:%d append:%p size:%zu :%s",
		d.name,
		this,
		int(fd),
		data(s),
		size(s),
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': wfile:%p DIRECT fd:%d append:%p size:%zu :%s",
		d.name,
		this,
		int(fd),
		data(s),
		size(s),
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::writable_file_direct::PositionedAppend(const Slice &s,
                                                                uint64_t offset)
noexcept
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p DIRECT fd:%d append:%p%s bytes:%zu%s offset:%zu%s",
		d.name,
		this,
		int(fd),
		data(s),
		aligned(data(s))? "" : "#AC",
		size(s),
		aligned(size(s))? "" : "#AC",
		offset,
		aligned(offset)? "" : "#AC"
	};
	#endif

	return rocksdb::Status::NotSupported();
}

uint64_t
ircd::db::database::env::writable_file_direct::GetFileSize()
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::lock_guard lock{mutex};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p DIRECT fd:%d get file size",
		d.name,
		this,
		int(fd)
	};
	#endif

	const auto &ret
	{
		logical_offset
	};

	assert(ret <= fs::size(fd));
	return ret;
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': wfile:%p DIRECT fd:%d get file size :%s",
		d.name,
		this,
		int(fd),
		e.what()
	};

	return 0;
}

/// (Internal) Append buffer. This function is the internal entry interface
/// for appending a buffer of any size and alignment to the file. It is
/// internal because it does no locking or error handling back to rocksdb,
/// because it's expected to be called from some virtual override which does
/// those things. This function will branch off as required to other internal
/// write_* functions to properly align and rebuffer the supplied buffer
/// eventually culminating in an aligned append to the file.
///
/// Calling this function will always result in some write to the file; even
/// if temporary buffering is used to achieve alignment; even if the entire
/// supplied buffer is hopelessly unaligned: the supplied data will be written
/// out some way or another during this call. This means there is no
/// requirement to care about flushing the temporary this->buffer after this
/// call is made. Note that the temporary this->buffer has no reason to be
/// touched by anything other than this function stack.
///
/// !!! NOTE !!!
/// There is a requirement to truncate the file after this call is made before
/// closing the file. If a crash occurs after a write() which was padded out
/// to the block alignment: the file size will reflect the padding when it is
/// opened at next startup; RocksDB will not detect its terminator character
/// sequence and consider this file corrupt.
/// !!!
///
/// - any offset
/// - any data
/// - any size
ircd::const_buffer
ircd::db::database::env::writable_file_direct::write(const const_buffer &buf_)
{
	const_buffer buf
	{
		aligned(logical_offset) && aligned(data(buf_))?
			write_aligned(buf_):
		!aligned(logical_offset)?
			write_unaligned_off(buf_):
			buf_
	};

	assert(aligned(logical_offset) || empty(buf));

	// buf can be empty here if it was entirely dealt with by the above
	// branches and there's nothing else to do here.
	if(empty(buf))
		return buf;

	// Branch on whether the buffer's address is aligned. If so, considering
	// the logical_offset is aligned here we are then finished.
	if(aligned(data(buf)))
		return write_aligned(buf);

	return write_unaligned_buf(buf);
}

/// * aligned offset
/// * unaligned data
/// - any size
ircd::const_buffer
ircd::db::database::env::writable_file_direct::write_unaligned_buf(const const_buffer &buf)
{
	assert(aligned(logical_offset));
	assert(!aligned(data(buf)));
	assert(!aligned(buf));

	// Window on the data between the given buffer's pointer and the next
	// alignment boundary.
	const const_buffer under_buf
	{
		data(buf), std::min(remain(uintptr_t(data(buf))), size(buf))
	};

	// Window on the data from the alignment boundary to the end of the
	// given buffer.
	const const_buffer remaining_buf
	{
		buf + size(under_buf)
	};

	assert(size(under_buf) <= size(buf));
	assert(size(under_buf) + size(remaining_buf) == size(buf));
	assert(data(buf) + size(under_buf) == data(remaining_buf));
	assert(aligned(data(remaining_buf)) || empty(remaining_buf));

	mutable_buffer dst(this->buffer);
	consume(dst, copy(dst, under_buf));
	consume(dst, copy(dst, remaining_buf));
	consume(dst, zero(dst));
	assert(empty(dst));

	// Flush the temporary buffer.
	_write__aligned(this->buffer, logical_offset);
	logical_offset += size(under_buf);
	return remaining_buf;
}

/// * unaligned offset
/// - any data
/// - any size
ircd::const_buffer
ircd::db::database::env::writable_file_direct::write_unaligned_off(const const_buffer &buf)
{
	assert(!aligned(logical_offset));

	// Window on the amount of buf we can take to fill up remaining space in
	// the temporary this->buffer
	const const_buffer src
	{
		data(buf), std::min(size(buf), buffer_remain())
	};

	// Window on the remaining space in the temporary this->buffer.
	const mutable_buffer dst
	{
		this->buffer + buffer_consumed()
	};

	// Window on the remaining space in dst after src is copied to dst, if any.
	const mutable_buffer pad
	{
		dst + size(src)
	};

	assert(size(dst) - size(pad) == size(src));
	assert(size(src) + size(pad) == buffer_remain());
	assert(size(src) + size(pad) + buffer_consumed() == alignment);
	assert(size(src) + buffer_consumed() != alignment || empty(pad));

	copy(dst, src);
	zero(pad);

	// Backtrack the logical_offset to the aligned offset where this->buffer's
	// data starts.
	const auto aligned_offset
	{
		align(logical_offset)
	};

	// Write the whole temporary this->buffer at the aligned offset.
	_write__aligned(this->buffer, aligned_offset);
	logical_offset += size(src);
	assert(aligned(logical_offset) || size(buf) < alignment);
	return const_buffer
	{
		buf + size(src)
	};
}

/// * aligned offset
/// * aligned data
/// - any size
ircd::const_buffer
ircd::db::database::env::writable_file_direct::write_aligned(const const_buffer &buf)
{
	assert(aligned(data(buf)));
	assert(aligned(logical_offset));

	// This portion at the end of buf did not fill out to the alignment.
	const const_buffer overflow
	{
		_write_aligned(buf, logical_offset)
	};

	// The aligned portion was written so the offset is incremented here.
	logical_offset += size(buf) - size(overflow);

	assert(aligned(logical_offset));
	assert(size(overflow) < alignment);
	assert(aligned(data(overflow)) || empty(overflow));
	assert(align(size(buf)) + size(overflow) == size(buf));
	assert(blocks(size(buf)) * alignment + size(overflow) == size(buf));

	if(!empty(overflow))
	{
		mutable_buffer dst(this->buffer);
		consume(dst, copy(dst, overflow));
		consume(dst, zero(dst));
		assert(empty(dst));

		_write__aligned(this->buffer, logical_offset);
		logical_offset += size(overflow);
		assert(!aligned(logical_offset));
	}

	return {};
}

/// * aligned data
/// * aligned offset
/// - any size
ircd::const_buffer
ircd::db::database::env::writable_file_direct::_write_aligned(const const_buffer &buf,
                                                              const uint64_t &offset)
{
	assert(aligned(data(buf)));
	assert(aligned(offset));

	// This portion will be written
	const const_buffer aligned_buf
	{
		data(buf), blocks(size(buf)) * alignment
	};

	// This trailing portion will be returned to caller
	const const_buffer ret
	{
		data(buf) + size(aligned_buf), size(buf) - size(aligned_buf)
	};

	assert(!empty(aligned_buf) || size(buf) < alignment);
	assert(size(aligned_buf) + size(ret) == size(buf));
	assert(size(ret) < alignment);
	if(empty(aligned_buf))
	{
		assert(size(ret) == size(buf));
		return ret;
	}

	_write__aligned(aligned_buf, offset);
	return ret;
}

/// * aligned offset
/// * aligned data
/// * aligned size
ircd::const_buffer
ircd::db::database::env::writable_file_direct::_write__aligned(const const_buffer &buf,
                                                               const uint64_t &offset)
{
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': wfile:%p DIRECT fd:%d write:%p%s bytes:%zu%s offset:%zu%s (logical:%zu)",
		d.name,
		this,
		int(fd),
		data(buf),
		aligned(data(buf))? "" : "#AC",
		size(buf),
		aligned(size(buf))? "" : "#AC",
		offset,
		aligned(offset)? "" : "#AC",
		logical_offset
	};
	#endif

	assert(aligned(buf));
	assert(aligned(offset));

	fs::write_opts wopts;
	wopts.priority = this->prio_val;
	wopts.nodelay = this->nodelay;
	wopts.offset = offset;
	fs::write(fd, buf, wopts);
	return {};
}

size_t
ircd::db::database::env::writable_file_direct::buffer_consumed()
const
{
	return likely(alignment != 0)?
		logical_offset % alignment:
		0UL;
}

size_t
ircd::db::database::env::writable_file_direct::buffer_remain()
const
{
	return remain(logical_offset);
}

size_t
ircd::db::database::env::writable_file_direct::blocks(const size_t &value)
const
{
	return likely(alignment != 0)?
		value / alignment:
		0UL;
}

size_t
ircd::db::database::env::writable_file_direct::remain(const size_t &value)
const
{
	return likely(alignment != 0)?
		alignment - (value - align(value)):
		0UL;
}

size_t
ircd::db::database::env::writable_file_direct::align(const size_t &value)
const
{
	return likely(alignment != 0)?
		value - (value % alignment):
		value;
}

bool
ircd::db::database::env::writable_file_direct::aligned(const const_buffer &buf)
const
{
	return buffer::aligned(buf, alignment);
}

bool
ircd::db::database::env::writable_file_direct::aligned(const void *const &value)
const
{
	return aligned(size_t(value));
}

bool
ircd::db::database::env::writable_file_direct::aligned(const size_t &value)
const
{
	return (alignment == 0) || (value % alignment == 0UL);
}

//
// sequential_file
//

decltype(ircd::db::database::env::sequential_file::default_opts)
ircd::db::database::env::sequential_file::default_opts{[]
{
	ircd::fs::fd::opts ret{std::ios_base::in};
	return ret;
}()};

ircd::db::database::env::sequential_file::sequential_file(database *const &d,
                                                          const std::string &name,
                                                          const EnvOptions &env_opts)
try
:d
{
	*d
}
,opts{[&env_opts]
{
	fs::fd::opts ret{default_opts};
	ret.direct = env_opts.use_direct_reads;
	return ret;
}()}
,fd
{
	name, this->opts
}
,_buffer_align
{
	opts.direct?
		fs::block_size(fd):
		1
}
,offset
{
	0
}
,aio
{
	// When this flag is false then AIO operations are never used for this
	// file; if true, AIO may be used if available and/or other conditions.
	// Currently the /proc filesystem doesn't like AIO.
	!startswith(name, "/proc/")
}
{
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': opened seqfile:%p fd:%d bs:%zu '%s'",
		d->name,
		this,
		int(fd),
		_buffer_align,
		name
	};
	#endif

	#if defined(HAVE_POSIX_FADVISE) && defined(POSIX_FADV_SEQUENTIAL)
	if(!opts.direct)
		syscall(::posix_fadvise, fd, offset, off_t(0), POSIX_FADV_SEQUENTIAL);
	#endif
}
catch(const std::system_error &e)
{
	// Set the level to downplay some errors which the user shouldn't
	// be alerted to with a log message under normal operations.
	const log::level level
	{
		is(e.code(), std::errc::no_such_file_or_directory)?
			log::level::DERROR:
			log::level::ERROR
	};

	log::logf
	{
		log, level, "'%s': opening seqfile:%p `%s' (%d) :%s",
		d->name,
		this,
		name,
		e.code().value(),
		e.what()
	};
}
catch(const std::exception &e)
{
	log::error
	{
		log, "'%s': opening seqfile:%p `%s' :%s",
		d->name,
		this,
		name,
		e.what()
	};
}

ircd::db::database::env::sequential_file::~sequential_file()
noexcept
{
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': close seqfile:%p fd:%d",
		d.name,
		this,
		int(fd)
	};
	#endif
}

rocksdb::Status
ircd::db::database::env::sequential_file::Read(size_t length,
                                               Slice *const result,
                                               char *const scratch)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::unique_lock lock
	{
		mutex, std::try_to_lock
	};

	// RocksDB sez that this call requires "External synchronization" i.e the
	// caller, not this class is responsible for exclusion. We assert anyway.
	if(unlikely(!bool(lock)))
		throw panic
		{
			"'%s': Unexpected concurrent access to seqfile %p",
			d.name,
			this
		};

	assert(result);
	assert(scratch);
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': seqfile:%p read:%p offset:%zu length:%zu scratch:%p",
		d.name,
		this,
		result,
		offset,
		length,
		scratch
	};
	#endif

	fs::read_opts opts;
	opts.offset = offset;
	opts.aio = this->aio;
	opts.all = false;
	const mutable_buffer buf
	{
		scratch, length
	};

	const const_buffer read
	{
		fs::read(fd, buf, opts)
	};

	*result = slice(read);
	this->offset += size(read);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': seqfile:%p read:%p offset:%zu length:%zu scratch:%p :%s",
		d.name,
		this,
		result,
		offset,
		length,
		scratch,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': seqfile:%p read:%p offset:%zu length:%zu scratch:%p :%s",
		d.name,
		this,
		result,
		offset,
		length,
		scratch,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::sequential_file::PositionedRead(uint64_t offset,
                                                         size_t length,
                                                         Slice *const result,
                                                         char *const scratch)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;
	const std::unique_lock lock
	{
		mutex, std::try_to_lock
	};

	if(unlikely(!bool(lock)))
		throw panic
		{
			"'%s': Unexpected concurrent access to seqfile %p",
			d.name,
			this
		};

	assert(result);
	assert(scratch);
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': seqfile:%p offset:%zu positioned read:%p offset:%zu length:%zu scratch:%p",
		d.name,
		this,
		this->offset,
		result,
		offset,
		length,
		scratch
	};
	#endif

	fs::read_opts opts;
	opts.offset = offset;
	opts.aio = this->aio;
	opts.all = false;
	const mutable_buffer buf
	{
		scratch, length
	};

	const const_buffer read
	{
		fs::read(fd, buf, opts)
	};

	*result = slice(read);
	this->offset = std::max(this->offset, off_t(offset + size(read)));
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': seqfile:%p positioned read:%p offset:%zu length:%zu scratch:%p :%s",
		d.name,
		this,
		result,
		offset,
		length,
		scratch,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': seqfile:%p positioned read:%p offset:%zu length:%zu scratch:%p :%s",
		d.name,
		this,
		result,
		offset,
		length,
		scratch,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::sequential_file::Skip(uint64_t size)
noexcept
{
	const ctx::uninterruptible::nothrow ui;
	const std::unique_lock lock
	{
		mutex, std::try_to_lock
	};

	// RocksDB sez that this call requires "External synchronization" i.e the
	// caller, not this class is responsible for exclusion. We assert anyway.
	if(unlikely(!bool(lock)))
		throw panic
		{
			"'%s': Unexpected concurrent access to seqfile %p",
			d.name,
			this
		};

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		"'%s': seqfile:%p offset:zu skip:%zu",
		d.name,
		this,
		offset,
		size
	};
	#endif

	offset += size;
	return Status::OK();
}

rocksdb::Status
ircd::db::database::env::sequential_file::InvalidateCache(size_t offset,
                                                          size_t length)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		"'%s': seqfile:%p invalidate cache offset:%zu length:%zu",
		d.name,
		this,
		offset,
		length
	};
	#endif

	if(opts.direct)
		return Status::OK();

	fs::evict(fd, length, offset);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		"'%s': seqfile:%p invalidate cache offset:%zu length:%zu :%s",
		d.name,
		this,
		offset,
		length,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		"'%s': seqfile:%p invalidate cache offset:%zu length:%zu :%s",
		d.name,
		this,
		offset,
		length,
		e.what()
	};

	return error_to_status{e};
}

bool
ircd::db::database::env::sequential_file::use_direct_io()
const noexcept
{
	return opts.direct;
}

size_t
ircd::db::database::env::sequential_file::GetRequiredBufferAlignment()
const noexcept
{
	const auto &ret
	{
		_buffer_align
	};

	return ret;
}

//
// random_access_file
//

decltype(ircd::db::database::env::random_access_file::default_opts)
ircd::db::database::env::random_access_file::default_opts{[]
{
	ircd::fs::fd::opts ret{std::ios_base::in};
	return ret;
}()};

ircd::db::database::env::random_access_file::random_access_file(database *const &d,
                                                                const std::string &name,
                                                                const EnvOptions &env_opts)
try
:d
{
	*d
}
,opts{[&env_opts]
{
	fs::fd::opts ret{default_opts};
	ret.direct = env_opts.use_direct_reads;
	return ret;
}()}
,fd
{
	name, this->opts
}
,_buffer_align
{
	opts.direct?
		fs::block_size(fd):
		1
}
,aio
{
	// When this flag is false then AIO operations are never used for this
	// file; if true, AIO may be used if available and/or other conditions.
	// Currently the /proc filesystem doesn't like AIO.
	!startswith(name, "/proc/")
}
{
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': opened rfile:%p fd:%d bs:%zu '%s'",
		d->name,
		this,
		int(fd),
		_buffer_align,
		name
	};
	#endif
}
catch(const std::exception &e)
{
	log::error
	{
		log, "'%s': opening rfile:%p `%s' :%s",
		d->name,
		this,
		name,
		e.what()
	};
}

ircd::db::database::env::random_access_file::~random_access_file()
noexcept
{
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': close rfile:%p fd:%d",
		d.name,
		this,
		int(fd)
	};
	#endif
}

rocksdb::Status
ircd::db::database::env::random_access_file::Prefetch(uint64_t offset,
                                                      size_t length)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': rfile:%p prefetch offset:%zu length:%zu",
		d.name,
		this,
		offset,
		length
	};
	#endif

	// Note RocksDB does not call our prefetch() when using direct IO.
	assert(!this->opts.direct);

	fs::prefetch(fd, length, offset);
	return Status::OK();
}
catch(const std::system_error &e)
{
	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': rfile:%p prefetch offset:%zu length:%zu :%s",
		d.name,
		this,
		offset,
		length,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::random_access_file::Read(uint64_t offset,
                                                  size_t length,
                                                  Slice *const result,
                                                  char *const scratch)
const noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	assert(result);
	assert(scratch);
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': rfile:%p read:%p offset:%zu length:%zu scratch:%p",
		d.name,
		this,
		result,
		offset,
		length,
		scratch
	};
	#endif

	fs::read_opts opts;
	opts.offset = offset;
	opts.aio = this->aio;
	opts.all = !this->opts.direct;
	const mutable_buffer buf
	{
		scratch, length
	};

	assert(!this->opts.direct || buffer::aligned(buf, _buffer_align));
	const auto read
	{
		fs::read(fd, buf, opts)
	};

	*result = slice(read);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': rfile:%p read:%p offset:%zu length:%zu scratch:%p :%s",
		d.name,
		this,
		result,
		offset,
		length,
		scratch,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': rfile:%p read:%p offset:%zu length:%zu scratch:%p :%s",
		d.name,
		this,
		result,
		offset,
		length,
		scratch,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::random_access_file::InvalidateCache(size_t offset,
                                                             size_t length)
noexcept
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': rfile:%p invalidate cache offset:%zu length:%zu",
		d.name,
		this,
		offset,
		length
	};
	#endif

	if(opts.direct)
		return Status::OK();

	fs::evict(fd, length, offset);
	return Status::OK();
}

size_t
ircd::db::database::env::random_access_file::GetUniqueId(char *const id,
                                                         size_t max_size)
const noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': rfile:%p get unique id:%p max_size:%zu",
		d.name,
		this,
		id,
		max_size
	};
	#endif

	const mutable_buffer buf
	{
		id, max_size
	};

	//return size(fs::uuid(fd, buf));
	return 0;
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': rfile:%p GetUniqueId id:%p max_size:%zu :%s",
		d.name,
		this,
		id,
		max_size,
		e.what()
	};

	return 0;
}

void
ircd::db::database::env::random_access_file::Hint(AccessPattern pattern)
noexcept
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': rfile:%p hint %s",
		d.name,
		this,
		reflect(pattern)
	};
	#endif
}

bool
ircd::db::database::env::random_access_file::use_direct_io()
const noexcept
{
	return opts.direct;
}

size_t
ircd::db::database::env::random_access_file::GetRequiredBufferAlignment()
const noexcept
{
	const auto &ret
	{
		_buffer_align
	};

	return ret;
}

//
// random_rw_file
//

decltype(ircd::db::database::env::random_rw_file::default_opts)
ircd::db::database::env::random_rw_file::default_opts{[]
{
	ircd::fs::fd::opts ret
	{
		std::ios_base::in | std::ios_base::out
	};

	return ret;
}()};

ircd::db::database::env::random_rw_file::random_rw_file(database *const &d,
                                                        const std::string &name,
                                                        const EnvOptions &env_opts)
try
:d
{
	*d
}
,opts{[&env_opts]
{
	fs::fd::opts ret{default_opts};
	ret.direct = env_opts.use_direct_reads && env_opts.use_direct_writes;
	return ret;
}()}
,fd
{
	name, this->opts
}
,_buffer_align
{
	opts.direct?
		fs::block_size(fd):
		1
}
,aio
{
	true
}
{
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': opened rwfile:%p fd:%d bs:%zu '%s'",
		d->name,
		this,
		int(fd),
		_buffer_align,
		name
	};
	#endif
}
catch(const std::exception &e)
{
	log::error
	{
		log, "'%s': opening rwfile:%p `%s' :%s",
		d->name,
		this,
		name,
		e.what()
	};
}

ircd::db::database::env::random_rw_file::~random_rw_file()
noexcept
{
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': close rwfile:%p fd:%d '%s'",
		d.name,
		this,
		int(fd)
	};
	#endif
}

rocksdb::Status
ircd::db::database::env::random_rw_file::Close()
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': close rwfile:%p fd:%d '%s'",
		d.name,
		this,
		int(fd)
	};
	#endif

	this->fd = fs::fd{};
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		"'%s': rwfile:%p close :%s",
		d.name,
		this,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		"'%s': rwfile:%p close :%s",
		d.name,
		this,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::random_rw_file::Fsync()
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': rwfile:%p fd:%d fsync",
		d.name,
		int(fd),
		this
	};
	#endif

	fs::sync_opts opts;
	fs::flush(fd, opts);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		"'%s': rwfile:%p fd:%d fsync :%s",
		d.name,
		this,
		int(fd),
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		"'%s': rwfile:%p fd:%d fsync :%s",
		d.name,
		this,
		int(fd),
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::random_rw_file::Sync()
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': rwfile:%p fd:%d sync",
		d.name,
		int(fd),
		this
	};
	#endif

	fs::sync_opts opts;
	fs::sync(fd, opts);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		"'%s': rwfile:%p fd:%d sync :%s",
		d.name,
		this,
		int(fd),
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		"'%s': rwfile:%p fd:%d sync :%s",
		d.name,
		this,
		int(fd),
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::random_rw_file::Flush()
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': rwfile:%p fd:%d flush",
		d.name,
		int(fd),
		this
	};
	#endif

	fs::sync_opts opts;
	opts.metadata = false;
	fs::flush(fd, opts);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		"'%s': rwfile:%p fd:%d flush :%s",
		d.name,
		this,
		int(fd),
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		"'%s': rwfile:%p fd:%d flush :%s",
		d.name,
		this,
		int(fd),
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::random_rw_file::Read(uint64_t offset,
                                              size_t length,
                                              Slice *const result,
                                              char *const scratch)
const noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	assert(result);
	assert(scratch);
	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': rwfile:%p read:%p offset:%zu length:%zu scratch:%p",
		d.name,
		this,
		result,
		offset,
		length,
		scratch
	};
	#endif

	fs::read_opts opts;
	opts.offset = offset;
	opts.aio = this->aio;
	opts.all = !this->opts.direct;
	const mutable_buffer buf
	{
		scratch, length
	};

	const auto read
	{
		fs::read(fd, buf, opts)
	};

	*result = slice(read);
	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': rwfile:%p read:%p offset:%zu length:%zu scratch:%p :%s",
		d.name,
		this,
		result,
		offset,
		length,
		scratch,
		e.what()
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': rwfile:%p read:%p offset:%zu length:%zu scratch:%p :%s",
		d.name,
		this,
		result,
		offset,
		length,
		scratch,
		e.what()
	};

	return error_to_status{e};
}

rocksdb::Status
ircd::db::database::env::random_rw_file::Write(uint64_t offset,
                                               const Slice &slice)
noexcept try
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': rwfile:%p fd:%d write:%p length:%zu offset:%zu",
		d.name,
		this,
		int(fd),
		data(slice),
		size(slice),
		offset
	};
	#endif

	const const_buffer buf
	{
		data(slice), size(slice)
	};

	const auto read
	{
		fs::write(fd, buf, offset)
	};

	return Status::OK();
}
catch(const std::system_error &e)
{
	log::error
	{
		log, "'%s': rwfile:%p fd:%d write:%p length:%zu offset:%zu",
		d.name,
		this,
		int(fd),
		data(slice),
		size(slice),
		offset
	};

	return error_to_status{e};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': rwfile:%p fd:%d write:%p length:%zu offset:%zu",
		d.name,
		this,
		int(fd),
		data(slice),
		size(slice),
		offset
	};

	return error_to_status{e};
}

bool
ircd::db::database::env::random_rw_file::use_direct_io()
const noexcept
{
	return opts.direct;
}

size_t
ircd::db::database::env::random_rw_file::GetRequiredBufferAlignment()
const noexcept
{
	const auto &ret
	{
		_buffer_align
	};

	return ret;
}

//
// directory
//

ircd::db::database::env::directory::directory(database *const &d,
                                              const std::string &name,
                                              std::unique_ptr<Directory> defaults)
:d{*d}
,defaults{std::move(defaults)}
{
}

ircd::db::database::env::directory::~directory()
noexcept
{
}

rocksdb::Status
ircd::db::database::env::directory::Fsync()
noexcept
{
	const ctx::uninterruptible::nothrow ui;

	#ifdef RB_DEBUG_DB_ENV
	log::debug
	{
		log, "'%s': directory:%p fsync",
		d.name,
		this
	};
	#endif

	return defaults->Fsync();
}

//
// file_lock
//

ircd::db::database::env::file_lock::file_lock(database *const &d)
:d{*d}
{
}

ircd::db::database::env::file_lock::~file_lock()
noexcept
{
}

///////////////////////////////////////////////////////////////////////////////
//
// db/database/env/state.h
//

//
// env::state::state
//

ircd::db::database::env::state::state(database *const &d)
:d{*d}
{
	for(size_t i(0); i < pool.size(); ++i)
		pool.at(i) = std::make_unique<struct pool>(this->d, Priority(i));
}

ircd::db::database::env::state::~state()
noexcept
{
	log::debug
	{
		log, "'%s': Shutting down environment...",
		d.name
	};
}

//
// state::pool
//

decltype(ircd::db::database::env::state::pool::stack_size)
ircd::db::database::env::state::pool::stack_size
{
	{ "name",     "ircd.db.env.pool.stack_size" },
	{ "default",  long(128_KiB)                 },
};

//
// state::pool::pool
//

ircd::db::database::env::state::pool::pool(database &d,
                                           const Priority &pri)
:d{d}
,pri{pri}
,iopri
{
	pri == Priority::HIGH?
		IOPriority::IO_HIGH:
		IOPriority::IO_LOW
}
,popts
{
	size_t(stack_size),    // stack size of worker
	0,                     // initial workers
	-1,                    // queue hard limit
	-1,                    // queue soft limit
}
,p
{
	reflect(pri),  // name of pool
	this->popts    // pool options
}
{
}

ircd::db::database::env::state::pool::~pool()
noexcept
{
	join();
}

void
ircd::db::database::env::state::pool::join()
try
{
	if(!tasks.empty() || p.pending())
		log::warning
		{
			log, "'%s': Waiting for tasks:%zu queued:%zu active:%zu in pool '%s'",
			d.name,
			tasks.size(),
			p.queued(),
			p.active(),
			ctx::name(p)
		};

	this->wait();
	assert(!p.pending());
	assert(tasks.empty());
	p.join();

	log::debug
	{
		log, "'%s': Terminated pool '%s'.",
		d.name,
		ctx::name(p)
	};
}
catch(const std::exception &e)
{
	log::critical
	{
		log, "'%s': Environment pool '%s' join :%s",
		d.name,
		ctx::name(p),
		e.what()
	};

	throw;
}

void
ircd::db::database::env::state::pool::wait()
{
	dock.wait([this]
	{
		return tasks.empty() && !p.pending();
	});
}

void
ircd::db::database::env::state::pool::operator()(task &&task)
{
	assert(task._id == 0);
	task._id = ++taskctr;
	tasks.emplace_back(std::move(task));
	p([this]
	{
		if(tasks.empty())
			return;

		// Don't start a background task before RUN.
		run::changed::dock.wait([]
		{
			return run::level != run::level::START;
		});

		const ctx::uninterruptible::nothrow ui;
		const auto task{std::move(tasks.front())};
		tasks.pop_front();

		log::debug
		{
			log, "'%s': pool:%s queue:%zu starting task:%lu func:%p arg:%p",
			this->d.name,
			ctx::name(p),
			tasks.size(),
			task._id,
			task.func,
			task.arg,
		};

		const ctx::slice_usage_warning message
		{
			"'%s': pool:%s task:%p",
			this->d.name,
			ctx::name(p),
			task.func
		};

		// Execute the task
		task.func(task.arg);

		log::debug
		{
			log, "'%s': pool:%s queue:%zu finished task:%zu func:%p arg:%p",
			this->d.name,
			ctx::name(p),
			tasks.size(),
			task._id,
			task.func,
			task.arg,
		};

		dock.notify_all();
	});
}

size_t
ircd::db::database::env::state::pool::cancel(void *const &tag)
{
	size_t i(0);
	auto it(begin(tasks));
	while(it != end(tasks))
	{
		auto &task(*it);
		log::debug
		{
			log, "'%s': pool:%s tasks:%zu cancel#%zu task:%lu func:%p cancel:%p arg:%p tag:%p",
			d.name,
			ctx::name(p),
			tasks.size(),
			i,
			task._id,
			task.func,
			task.cancel,
			task.arg,
			tag
		};

		task.cancel(task.arg);
		it = tasks.erase(it);
		++i;
	}

	dock.notify_all();
	return i;
}