input/nfs: use the asynchronous libnfs API

More robust and cancellable.

11 files changed, 1398 insertions, 0 deletions

diff --git a/src/lib/nfs/Callback.hxx b/src/lib/nfs/Callback.hxx
new file mode 100644
index 000000000..ae82ecc3c
--- /dev/null
+++ b/src/lib/nfs/Callback.hxx
@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_NFS_CALLBACK_HXX
+#define MPD_NFS_CALLBACK_HXX
+
+#include "check.h"
+
+class Error;
+
+class NfsCallback {
+public:
+	virtual void OnNfsCallback(unsigned status, void *data) = 0;
+	virtual void OnNfsError(Error &&error) = 0;
+};
+
+#endif
diff --git a/src/lib/nfs/Cancellable.hxx b/src/lib/nfs/Cancellable.hxx
new file mode 100644
index 000000000..50762b582
--- /dev/null
+++ b/src/lib/nfs/Cancellable.hxx
@@ -0,0 +1,177 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_NFS_CANCELLABLE_HXX
+#define MPD_NFS_CANCELLABLE_HXX
+
+#include "Compiler.h"
+
+#include <list>
+#include <algorithm>
+
+#include <assert.h>
+
+template<typename T>
+class CancellablePointer {
+public:
+	typedef T *pointer_type;
+	typedef T &reference_type;
+	typedef const T &const_reference_type;
+
+private:
+	pointer_type p;
+
+public:
+	explicit constexpr CancellablePointer(reference_type _p):p(&_p) {}
+
+	CancellablePointer(const CancellablePointer &) = delete;
+
+	constexpr bool IsCancelled() const {
+		return p == nullptr;
+	}
+
+	void Cancel() {
+		assert(!IsCancelled());
+
+		p = nullptr;
+	}
+
+	reference_type Get() {
+		assert(p != nullptr);
+
+		return *p;
+	}
+
+	constexpr bool Is(const_reference_type other) const {
+		return p == &other;
+	}
+};
+
+template<typename T, typename CT=CancellablePointer<T>>
+class CancellableList {
+public:
+	typedef typename CT::reference_type reference_type;
+	typedef typename CT::const_reference_type const_reference_type;
+
+private:
+	typedef std::list<CT> List;
+	typedef typename List::iterator iterator;
+	typedef typename List::const_iterator const_iterator;
+	List list;
+
+	class MatchPointer {
+		const_reference_type p;
+
+	public:
+		explicit constexpr MatchPointer(const_reference_type _p)
+			:p(_p) {}
+
+		constexpr bool operator()(const CT &a) const {
+			return a.Is(p);
+		}
+	};
+
+	gcc_pure
+	iterator Find(reference_type p) {
+		return std::find_if(list.begin(), list.end(), MatchPointer(p));
+	}
+
+	gcc_pure
+	const_iterator Find(const_reference_type p) const {
+		return std::find_if(list.begin(), list.end(), MatchPointer(p));
+	}
+
+	class MatchReference {
+		const CT &c;
+
+	public:
+		constexpr explicit MatchReference(const CT &_c):c(_c) {}
+
+		gcc_pure
+		bool operator()(const CT &a) const {
+			return &a == &c;
+		}
+	};
+
+	gcc_pure
+	iterator Find(CT &c) {
+		return std::find_if(list.begin(), list.end(),
+				    MatchReference(c));
+	}
+
+	gcc_pure
+	const_iterator Find(const CT &c) const {
+		return std::find_if(list.begin(), list.end(),
+				    MatchReference(c));
+	}
+
+public:
+#ifndef NDEBUG
+	gcc_pure
+	bool IsEmpty() const {
+		for (const auto &c : list)
+			if (!c.IsCancelled())
+				return false;
+
+		return true;
+	}
+#endif
+
+	gcc_pure
+	bool Contains(const_reference_type p) const {
+		return Find(p) != list.end();
+	}
+
+	template<typename... Args>
+	CT &Add(reference_type p, Args&&... args) {
+		assert(Find(p) == list.end());
+
+		list.emplace_back(p, std::forward<Args>(args)...);
+		return list.back();
+	}
+
+	void RemoveLast() {
+		list.pop_back();
+	}
+
+	bool RemoveOptional(CT &ct) {
+		auto i = Find(ct);
+		if (i == list.end())
+			return false;
+
+		list.erase(i);
+		return true;
+	}
+
+	void Remove(CT &ct) {
+		auto i = Find(ct);
+		assert(i != list.end());
+
+		list.erase(i);
+	}
+
+	void Cancel(reference_type p) {
+		auto i = Find(p);
+		assert(i != list.end());
+
+		i->Cancel();
+	}
+};
+
+#endif
diff --git a/src/lib/nfs/Connection.cxx b/src/lib/nfs/Connection.cxx
new file mode 100644
index 000000000..4c2f523f6
--- /dev/null
+++ b/src/lib/nfs/Connection.cxx
@@ -0,0 +1,415 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "Connection.hxx"
+#include "Lease.hxx"
+#include "Domain.hxx"
+#include "Callback.hxx"
+#include "system/fd_util.h"
+#include "util/Error.hxx"
+#include "event/Call.hxx"
+
+extern "C" {
+#include <nfsc/libnfs.h>
+}
+
+#include <utility>
+
+inline bool
+NfsConnection::CancellableCallback::Open(nfs_context *ctx,
+					 const char *path, int flags,
+					 Error &error)
+{
+	int result = nfs_open_async(ctx, path, flags,
+				    Callback, this);
+	if (result < 0) {
+		error.Format(nfs_domain, "nfs_open_async() failed: %s",
+			     nfs_get_error(ctx));
+		return false;
+	}
+
+	return true;
+}
+
+inline bool
+NfsConnection::CancellableCallback::Stat(nfs_context *ctx,
+					 struct nfsfh *fh,
+					 Error &error)
+{
+	int result = nfs_fstat_async(ctx, fh, Callback, this);
+	if (result < 0) {
+		error.Format(nfs_domain, "nfs_fstat_async() failed: %s",
+			     nfs_get_error(ctx));
+		return false;
+	}
+
+	return true;
+}
+
+inline bool
+NfsConnection::CancellableCallback::Read(nfs_context *ctx, struct nfsfh *fh,
+					 uint64_t offset, size_t size,
+					 Error &error)
+{
+	int result = nfs_pread_async(ctx, fh, offset, size, Callback, this);
+	if (result < 0) {
+		error.Format(nfs_domain, "nfs_pread_async() failed: %s",
+			     nfs_get_error(ctx));
+		return false;
+	}
+
+	return true;
+}
+
+inline void
+NfsConnection::CancellableCallback::Callback(int err, void *data)
+{
+	if (!IsCancelled()) {
+		NfsCallback &cb = Get();
+
+		connection.callbacks.Remove(*this);
+
+		if (err >= 0)
+			cb.OnNfsCallback((unsigned)err, data);
+		else
+			cb.OnNfsError(Error(nfs_domain, err,
+					    (const char *)data));
+	} else {
+		connection.callbacks.Remove(*this);
+	}
+}
+
+void
+NfsConnection::CancellableCallback::Callback(int err,
+					     gcc_unused struct nfs_context *nfs,
+					     void *data, void *private_data)
+{
+	CancellableCallback &c = *(CancellableCallback *)private_data;
+	c.Callback(err, data);
+}
+
+static constexpr unsigned
+libnfs_to_events(int i)
+{
+	return ((i & POLLIN) ? SocketMonitor::READ : 0) |
+		((i & POLLOUT) ? SocketMonitor::WRITE : 0);
+}
+
+static constexpr int
+events_to_libnfs(unsigned i)
+{
+	return ((i & SocketMonitor::READ) ? POLLIN : 0) |
+		((i & SocketMonitor::WRITE) ? POLLOUT : 0);
+}
+
+NfsConnection::~NfsConnection()
+{
+	assert(new_leases.empty());
+	assert(active_leases.empty());
+	assert(callbacks.IsEmpty());
+
+	if (context != nullptr)
+		BlockingCall(SocketMonitor::GetEventLoop(), [this](){
+				DestroyContext();
+			});
+}
+
+void
+NfsConnection::AddLease(NfsLease &lease)
+{
+	{
+		const ScopeLock protect(mutex);
+		new_leases.push_back(&lease);
+	}
+
+	DeferredMonitor::Schedule();
+}
+
+void
+NfsConnection::RemoveLease(NfsLease &lease)
+{
+	const ScopeLock protect(mutex);
+
+	new_leases.remove(&lease);
+	active_leases.remove(&lease);
+}
+
+bool
+NfsConnection::Open(const char *path, int flags, NfsCallback &callback,
+		    Error &error)
+{
+	assert(!callbacks.Contains(callback));
+
+	auto &c = callbacks.Add(callback, *this);
+	if (!c.Open(context, path, flags, error)) {
+		callbacks.RemoveLast();
+		return false;
+	}
+
+	ScheduleSocket();
+	return true;
+}
+
+bool
+NfsConnection::Stat(struct nfsfh *fh, NfsCallback &callback, Error &error)
+{
+	assert(!callbacks.Contains(callback));
+
+	auto &c = callbacks.Add(callback, *this);
+	if (!c.Stat(context, fh, error)) {
+		callbacks.RemoveLast();
+		return false;
+	}
+
+	ScheduleSocket();
+	return true;
+}
+
+bool
+NfsConnection::Read(struct nfsfh *fh, uint64_t offset, size_t size,
+		    NfsCallback &callback, Error &error)
+{
+	assert(!callbacks.Contains(callback));
+
+	auto &c = callbacks.Add(callback, *this);
+	if (!c.Read(context, fh, offset, size, error)) {
+		callbacks.RemoveLast();
+		return false;
+	}
+
+	ScheduleSocket();
+	return true;
+}
+
+void
+NfsConnection::Cancel(NfsCallback &callback)
+{
+	callbacks.Cancel(callback);
+}
+
+static void
+DummyCallback(int, struct nfs_context *, void *, void *)
+{
+}
+
+void
+NfsConnection::Close(struct nfsfh *fh)
+{
+	nfs_close_async(context, fh, DummyCallback, nullptr);
+	ScheduleSocket();
+}
+
+void
+NfsConnection::DestroyContext()
+{
+	assert(context != nullptr);
+
+	SocketMonitor::Cancel();
+	nfs_destroy_context(context);
+	context = nullptr;
+}
+
+void
+NfsConnection::ScheduleSocket()
+{
+	assert(context != nullptr);
+
+	if (!SocketMonitor::IsDefined()) {
+		int _fd = nfs_get_fd(context);
+		fd_set_cloexec(_fd, true);
+		SocketMonitor::Open(_fd);
+	}
+
+	SocketMonitor::Schedule(libnfs_to_events(nfs_which_events(context)));
+}
+
+bool
+NfsConnection::OnSocketReady(unsigned flags)
+{
+	bool closed = false;
+
+	const bool was_mounted = mount_finished;
+	if (!mount_finished)
+		/* until the mount is finished, the NFS client may use
+		   various sockets, therefore we unregister and
+		   re-register it each time */
+		SocketMonitor::Steal();
+
+	assert(!in_event);
+	in_event = true;
+
+	assert(!in_service);
+	in_service = true;
+	postponed_destroy = false;
+
+	int result = nfs_service(context, events_to_libnfs(flags));
+
+	assert(context != nullptr);
+	assert(in_service);
+	in_service = false;
+
+	if (postponed_destroy) {
+		/* somebody has called nfs_client_free() while we were inside
+		   nfs_service() */
+		const ScopeLock protect(mutex);
+		DestroyContext();
+		closed = true;
+		// TODO? nfs_client_cleanup_files(client);
+	} else if (!was_mounted && mount_finished) {
+		const ScopeLock protect(mutex);
+
+		if (postponed_mount_error.IsDefined()) {
+			DestroyContext();
+			closed = true;
+			BroadcastMountError(std::move(postponed_mount_error));
+		} else if (result == 0)
+			BroadcastMountSuccess();
+	} else if (result < 0) {
+		/* the connection has failed */
+		Error error;
+		error.Format(nfs_domain, "NFS connection has failed: %s",
+			     nfs_get_error(context));
+
+		const ScopeLock protect(mutex);
+
+		DestroyContext();
+		closed = true;
+
+		if (!mount_finished)
+			BroadcastMountError(std::move(error));
+		else
+			BroadcastError(std::move(error));
+	}
+
+	assert(in_event);
+	in_event = false;
+
+	if (context != nullptr)
+		ScheduleSocket();
+
+	return !closed;
+}
+
+inline void
+NfsConnection::MountCallback(int status, gcc_unused nfs_context *nfs,
+			     gcc_unused void *data)
+{
+	assert(context == nfs);
+
+	mount_finished = true;
+
+	if (status < 0) {
+		postponed_mount_error.Set(nfs_domain, status,
+					  "nfs_mount_async() failed");
+		return;
+	}
+}
+
+void
+NfsConnection::MountCallback(int status, nfs_context *nfs, void *data,
+			     void *private_data)
+{
+	NfsConnection *c = (NfsConnection *)private_data;
+
+	c->MountCallback(status, nfs, data);
+}
+
+inline bool
+NfsConnection::MountInternal(Error &error)
+{
+	if (context != nullptr)
+		return true;
+
+	context = nfs_init_context();
+	if (context == nullptr) {
+		error.Set(nfs_domain, "nfs_init_context() failed");
+		return false;
+	}
+
+	postponed_mount_error.Clear();
+	mount_finished = false;
+	in_service = false;
+	in_event = false;
+
+	if (nfs_mount_async(context, server.c_str(), export_name.c_str(),
+			    MountCallback, this) != 0) {
+		error.Format(nfs_domain,
+			     "nfs_mount_async() failed: %s",
+			     nfs_get_error(context));
+		nfs_destroy_context(context);
+		context = nullptr;
+		return false;
+	}
+
+	ScheduleSocket();
+	return true;
+}
+
+void
+NfsConnection::BroadcastMountSuccess()
+{
+	while (!new_leases.empty()) {
+		auto i = new_leases.begin();
+		active_leases.splice(active_leases.end(), new_leases, i);
+		(*i)->OnNfsConnectionReady();
+	}
+}
+
+void
+NfsConnection::BroadcastMountError(Error &&error)
+{
+	while (!new_leases.empty()) {
+		auto l = new_leases.front();
+		new_leases.pop_front();
+		l->OnNfsConnectionFailed(error);
+	}
+
+	OnNfsConnectionError(std::move(error));
+}
+
+void
+NfsConnection::BroadcastError(Error &&error)
+{
+	while (!active_leases.empty()) {
+		auto l = active_leases.front();
+		active_leases.pop_front();
+		l->OnNfsConnectionDisconnected(error);
+	}
+
+	BroadcastMountError(std::move(error));
+}
+
+void
+NfsConnection::RunDeferred()
+{
+	{
+		Error error;
+		if (!MountInternal(error)) {
+			const ScopeLock protect(mutex);
+			BroadcastMountError(std::move(error));
+			return;
+		}
+	}
+
+	if (mount_finished) {
+		const ScopeLock protect(mutex);
+		BroadcastMountSuccess();
+	}
+}
diff --git a/src/lib/nfs/Connection.hxx b/src/lib/nfs/Connection.hxx
new file mode 100644
index 000000000..8850ff6f3
--- /dev/null
+++ b/src/lib/nfs/Connection.hxx
@@ -0,0 +1,160 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_NFS_CONNECTION_HXX
+#define MPD_NFS_CONNECTION_HXX
+
+#include "Lease.hxx"
+#include "Cancellable.hxx"
+#include "thread/Mutex.hxx"
+#include "event/SocketMonitor.hxx"
+#include "event/DeferredMonitor.hxx"
+#include "util/Error.hxx"
+
+#include <string>
+#include <list>
+
+struct nfs_context;
+class NfsCallback;
+
+/**
+ * An asynchronous connection to a NFS server.
+ */
+class NfsConnection : SocketMonitor, DeferredMonitor {
+	class CancellableCallback : public CancellablePointer<NfsCallback> {
+		NfsConnection &connection;
+
+	public:
+		explicit constexpr CancellableCallback(NfsCallback &_callback,
+						       NfsConnection &_connection)
+			:CancellablePointer<NfsCallback>(_callback),
+			 connection(_connection) {}
+
+		bool Open(nfs_context *context, const char *path, int flags,
+			  Error &error);
+		bool Stat(nfs_context *context, struct nfsfh *fh,
+			  Error &error);
+		bool Read(nfs_context *context, struct nfsfh *fh,
+			  uint64_t offset, size_t size,
+			  Error &error);
+
+	private:
+		static void Callback(int err, struct nfs_context *nfs,
+				     void *data, void *private_data);
+		void Callback(int err, void *data);
+	};
+
+	std::string server, export_name;
+
+	nfs_context *context;
+
+	Mutex mutex;
+
+	typedef std::list<NfsLease *> LeaseList;
+	LeaseList new_leases, active_leases;
+
+	typedef CancellableList<NfsCallback, CancellableCallback> CallbackList;
+	CallbackList callbacks;
+
+	Error postponed_mount_error;
+
+	/**
+	 * True when nfs_service() is being called.  During that,
+	 * nfs_client_free() is postponed, or libnfs will crash.  See
+	 * #postponed_destroy.
+	 */
+	bool in_service;
+
+	/**
+	 * True when OnSocketReady() is being called.  During that,
+	 * event updates are omitted.
+	 */
+	bool in_event;
+
+	/**
+	 * True when nfs_client_free() has been called while #in_service
+	 * was true.
+	 */
+	bool postponed_destroy;
+
+	bool mount_finished;
+
+public:
+	gcc_nonnull_all
+	NfsConnection(EventLoop &_loop,
+		      const char *_server, const char *_export_name)
+		:SocketMonitor(_loop), DeferredMonitor(_loop),
+		 server(_server), export_name(_export_name),
+		 context(nullptr) {}
+
+	~NfsConnection();
+
+	gcc_pure
+	const char *GetServer() const {
+		return server.c_str();
+	}
+
+	gcc_pure
+	const char *GetExportName() const {
+		return export_name.c_str();
+	}
+
+	/**
+	 * Ensure that the connection is established.  The connection
+	 * is kept up while at least one #NfsLease is registered.
+	 *
+	 * This method is thread-safe.  However, #NfsLease's methods
+	 * will be invoked from within the #EventLoop's thread.
+	 */
+	void AddLease(NfsLease &lease);
+	void RemoveLease(NfsLease &lease);
+
+	bool Open(const char *path, int flags, NfsCallback &callback,
+		  Error &error);
+	bool Stat(struct nfsfh *fh, NfsCallback &callback, Error &error);
+	bool Read(struct nfsfh *fh, uint64_t offset, size_t size,
+		  NfsCallback &callback, Error &error);
+	void Cancel(NfsCallback &callback);
+
+	void Close(struct nfsfh *fh);
+
+protected:
+	virtual void OnNfsConnectionError(Error &&error) = 0;
+
+private:
+	void DestroyContext();
+	bool MountInternal(Error &error);
+	void BroadcastMountSuccess();
+	void BroadcastMountError(Error &&error);
+	void BroadcastError(Error &&error);
+
+	static void MountCallback(int status, nfs_context *nfs, void *data,
+				  void *private_data);
+	void MountCallback(int status, nfs_context *nfs, void *data);
+
+	void ScheduleSocket();
+
+	/* virtual methods from SocketMonitor */
+	virtual bool OnSocketReady(unsigned flags) override;
+
+	/* virtual methods from DeferredMonitor */
+	virtual void RunDeferred() override;
+};
+
+#endif
diff --git a/src/lib/nfs/FileReader.cxx b/src/lib/nfs/FileReader.cxx
new file mode 100644
index 000000000..52d951fa6
--- /dev/null
+++ b/src/lib/nfs/FileReader.cxx
@@ -0,0 +1,244 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "FileReader.hxx"
+#include "Glue.hxx"
+#include "Connection.hxx"
+#include "Domain.hxx"
+#include "event/Call.hxx"
+#include "IOThread.hxx"
+#include "util/StringUtil.hxx"
+#include "util/Error.hxx"
+
+#include <utility>
+
+#include <assert.h>
+#include <string.h>
+#include <fcntl.h>
+
+NfsFileReader::NfsFileReader()
+	:DeferredMonitor(io_thread_get()), state(State::INITIAL)
+{
+}
+
+NfsFileReader::~NfsFileReader()
+{
+	assert(state == State::INITIAL);
+}
+
+void
+NfsFileReader::Close()
+{
+	if (state == State::INITIAL)
+		return;
+
+	if (state == State::DEFER) {
+		state = State::INITIAL;
+		DeferredMonitor::Cancel();
+		return;
+	}
+
+	connection->RemoveLease(*this);
+
+	if (state > State::MOUNT && state != State::IDLE)
+		connection->Cancel(*this);
+
+	if (state > State::OPEN)
+		connection->Close(fh);
+
+	state = State::INITIAL;
+}
+
+void
+NfsFileReader::DeferClose()
+{
+	BlockingCall(io_thread_get(), [this](){ Close(); });
+}
+
+bool
+NfsFileReader::Open(const char *uri, Error &error)
+{
+	assert(state == State::INITIAL);
+
+	if (!StringStartsWith(uri, "nfs://")) {
+		error.Set(nfs_domain, "Malformed nfs:// URI");
+		return false;
+	}
+
+	uri += 6;
+
+	const char *slash = strchr(uri, '/');
+	if (slash == nullptr) {
+		error.Set(nfs_domain, "Malformed nfs:// URI");
+		return false;
+	}
+
+	server = std::string(uri, slash);
+
+	uri = slash;
+	slash = strrchr(uri + 1, '/');
+	if (slash == nullptr || slash[1] == 0) {
+		error.Set(nfs_domain, "Malformed nfs:// URI");
+		return false;
+	}
+
+	export_name = std::string(uri, slash);
+	path = slash;
+
+	state = State::DEFER;
+	DeferredMonitor::Schedule();
+	return true;
+}
+
+bool
+NfsFileReader::Read(uint64_t offset, size_t size, Error &error)
+{
+	assert(state == State::IDLE);
+
+	if (!connection->Read(fh, offset, size, *this, error))
+		return false;
+
+	state = State::READ;
+	return true;
+}
+
+void
+NfsFileReader::CancelRead()
+{
+	if (state == State::READ) {
+		connection->Cancel(*this);
+		state = State::IDLE;
+	}
+}
+
+void
+NfsFileReader::OnNfsConnectionReady()
+{
+	assert(state == State::MOUNT);
+
+	Error error;
+	if (!connection->Open(path, O_RDONLY, *this, error)) {
+		OnNfsFileError(std::move(error));
+		return;
+	}
+
+	state = State::OPEN;
+}
+
+void
+NfsFileReader::OnNfsConnectionFailed(const Error &error)
+{
+	assert(state == State::MOUNT);
+
+	Error copy;
+	copy.Set(error);
+	OnNfsFileError(std::move(copy));
+}
+
+void
+NfsFileReader::OnNfsConnectionDisconnected(const Error &error)
+{
+	assert(state > State::MOUNT);
+
+	state = State::INITIAL;
+
+	Error copy;
+	copy.Set(error);
+	OnNfsFileError(std::move(copy));
+}
+
+inline void
+NfsFileReader::OpenCallback(nfsfh *_fh)
+{
+	assert(state == State::OPEN);
+	assert(connection != nullptr);
+	assert(_fh != nullptr);
+
+	fh = _fh;
+
+	Error error;
+	if (!connection->Stat(fh, *this, error)) {
+		OnNfsFileError(std::move(error));
+		return;
+	}
+
+	state = State::STAT;
+}
+
+inline void
+NfsFileReader::StatCallback(const struct stat *st)
+{
+	assert(state == State::STAT);
+	assert(connection != nullptr);
+	assert(fh != nullptr);
+	assert(st != nullptr);
+
+	if (!S_ISREG(st->st_mode)) {
+		OnNfsFileError(Error(nfs_domain, "Not a regular file"));
+		return;
+	}
+
+	state = State::IDLE;
+
+	OnNfsFileOpen(st->st_size);
+}
+
+void
+NfsFileReader::OnNfsCallback(unsigned status, void *data)
+{
+	switch (state) {
+	case State::INITIAL:
+	case State::DEFER:
+	case State::MOUNT:
+	case State::IDLE:
+		assert(false);
+		gcc_unreachable();
+
+	case State::OPEN:
+		OpenCallback((struct nfsfh *)data);
+		break;
+
+	case State::STAT:
+		StatCallback((const struct stat *)data);
+		break;
+
+	case State::READ:
+		state = State::IDLE;
+		OnNfsFileRead(data, status);
+		break;
+	}
+}
+
+void
+NfsFileReader::OnNfsError(Error &&error)
+{
+	OnNfsFileError(std::move(error));
+}
+
+void
+NfsFileReader::RunDeferred()
+{
+	assert(state == State::DEFER);
+
+	state = State::MOUNT;
+
+	connection = &nfs_get_connection(server.c_str(), export_name.c_str());
+	connection->AddLease(*this);
+}
diff --git a/src/lib/nfs/FileReader.hxx b/src/lib/nfs/FileReader.hxx
new file mode 100644
index 000000000..7f43e0ecf
--- /dev/null
+++ b/src/lib/nfs/FileReader.hxx
@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_NFS_FILE_READER_HXX
+#define MPD_NFS_FILE_READER_HXX
+
+#include "check.h"
+#include "Lease.hxx"
+#include "Callback.hxx"
+#include "event/DeferredMonitor.hxx"
+
+#include <string>
+
+#include <stdint.h>
+#include <stddef.h>
+#include <sys/stat.h>
+
+struct nfsfh;
+class NfsConnection;
+
+class NfsFileReader : NfsLease, NfsCallback, DeferredMonitor {
+	enum class State {
+		INITIAL,
+		DEFER,
+		MOUNT,
+		OPEN,
+		STAT,
+		READ,
+		IDLE,
+	};
+
+	State state;
+
+	std::string server, export_name;
+	const char *path;
+
+	NfsConnection *connection;
+
+	nfsfh *fh;
+
+public:
+	NfsFileReader();
+	~NfsFileReader();
+
+	void Close();
+	void DeferClose();
+
+	bool Open(const char *uri, Error &error);
+	bool Read(uint64_t offset, size_t size, Error &error);
+	void CancelRead();
+
+	bool IsIdle() const {
+		return state == State::IDLE;
+	}
+
+protected:
+	virtual void OnNfsFileOpen(uint64_t size) = 0;
+	virtual void OnNfsFileRead(const void *data, size_t size) = 0;
+	virtual void OnNfsFileError(Error &&error) = 0;
+
+private:
+	void OpenCallback(nfsfh *_fh);
+	void StatCallback(const struct stat *st);
+
+	/* virtual methods from NfsLease */
+	void OnNfsConnectionReady() final;
+	void OnNfsConnectionFailed(const Error &error) final;
+	void OnNfsConnectionDisconnected(const Error &error) final;
+
+	/* virtual methods from NfsCallback */
+	void OnNfsCallback(unsigned status, void *data) final;
+	void OnNfsError(Error &&error) final;
+
+	/* virtual methods from DeferredMonitor */
+	void RunDeferred() final;
+};
+
+#endif
diff --git a/src/lib/nfs/Glue.cxx b/src/lib/nfs/Glue.cxx
new file mode 100644
index 000000000..c043f06c6
--- /dev/null
+++ b/src/lib/nfs/Glue.cxx
@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "Glue.hxx"
+#include "Manager.hxx"
+#include "IOThread.hxx"
+#include "util/Manual.hxx"
+
+class NfsGlue {
+	NfsManager manager;
+
+public:
+	NfsGlue(EventLoop &_loop)
+		:manager(_loop) {}
+
+	~NfsGlue() {
+		//assert(open_uri.empty());
+	}
+
+	NfsConnection &GetConnection(const char *server, const char *export_name) {
+		return manager.GetConnection(server, export_name);
+	}
+};
+
+static Manual<NfsGlue> nfs_glue;
+static unsigned in_use;
+
+void
+nfs_init()
+{
+	if (in_use++ > 0)
+		return;
+
+	nfs_glue.Construct(io_thread_get());
+}
+
+void
+nfs_finish()
+{
+	assert(in_use > 0);
+
+	if (--in_use > 0)
+		return;
+
+	nfs_glue.Destruct();
+}
+
+NfsConnection &
+nfs_get_connection(const char *server, const char *export_name)
+{
+	return nfs_glue->GetConnection(server, export_name);
+}
diff --git a/src/lib/nfs/Glue.hxx b/src/lib/nfs/Glue.hxx
new file mode 100644
index 000000000..6da8957cb
--- /dev/null
+++ b/src/lib/nfs/Glue.hxx
@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_NFS_GLUE_HXX
+#define MPD_NFS_GLUE_HXX
+
+#include "check.h"
+#include "Compiler.h"
+
+class NfsConnection;
+
+void
+nfs_init();
+
+void
+nfs_finish();
+
+gcc_pure
+NfsConnection &
+nfs_get_connection(const char *server, const char *export_name);
+
+#endif
diff --git a/src/lib/nfs/Lease.hxx b/src/lib/nfs/Lease.hxx
new file mode 100644
index 000000000..6f88acf53
--- /dev/null
+++ b/src/lib/nfs/Lease.hxx
@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_NFS_LEASE_HXX
+#define MPD_NFS_LEASE_HXX
+
+#include "check.h"
+
+class Error;
+
+class NfsLease {
+public:
+	/**
+	 * The #NfsConnection has successfully mounted the server's
+	 * export and is ready for regular operation.
+	 */
+	virtual void OnNfsConnectionReady() = 0;
+
+	/**
+	 * The #NfsConnection has failed to mount the server's export.
+	 * This is being called instead of OnNfsConnectionReady().
+	 */
+	virtual void OnNfsConnectionFailed(const Error &error) = 0;
+
+	/**
+	 * The #NfsConnection has failed after OnNfsConnectionReady()
+	 * had been called already.
+	 */
+	virtual void OnNfsConnectionDisconnected(const Error &error) = 0;
+};
+
+#endif
diff --git a/src/lib/nfs/Manager.cxx b/src/lib/nfs/Manager.cxx
new file mode 100644
index 000000000..56a3fb79a
--- /dev/null
+++ b/src/lib/nfs/Manager.cxx
@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "Manager.hxx"
+#include "event/Loop.hxx"
+#include "Log.hxx"
+
+void
+NfsManager::ManagedConnection::OnNfsConnectionError(Error &&error)
+{
+	FormatError(error, "NFS error on %s:%s", GetServer(), GetExportName());
+
+	manager.connections.erase(Key(GetServer(), GetExportName()));
+}
+
+NfsConnection &
+NfsManager::GetConnection(const char *server, const char *export_name)
+{
+	assert(server != nullptr);
+	assert(export_name != nullptr);
+	assert(loop.IsInside());
+
+	const std::string key = Key(server, export_name);
+
+	auto e = connections.emplace(std::piecewise_construct,
+				     std::forward_as_tuple(key),
+				     std::forward_as_tuple(*this, loop,
+							   server,
+							   export_name));
+	return e.first->second;
+}
diff --git a/src/lib/nfs/Manager.hxx b/src/lib/nfs/Manager.hxx
new file mode 100644
index 000000000..4a380bd51
--- /dev/null
+++ b/src/lib/nfs/Manager.hxx
@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_NFS_MANAGER_HXX
+#define MPD_NFS_MANAGER_HXX
+
+#include "check.h"
+#include "Connection.hxx"
+
+#include <string>
+#include <map>
+
+/**
+ * A manager for NFS connections.  Handles multiple connections to
+ * multiple NFS servers.
+ */
+class NfsManager {
+	class ManagedConnection final : public NfsConnection {
+		NfsManager &manager;
+
+	public:
+		ManagedConnection(NfsManager &_manager, EventLoop &_loop,
+				  const char *_server,
+				  const char *_export_name)
+			:NfsConnection(_loop, _server, _export_name),
+			 manager(_manager) {}
+
+	protected:
+		/* virtual methods from NfsConnection */
+		void OnNfsConnectionError(Error &&error) override;
+	};
+
+	EventLoop &loop;
+
+	/**
+	 * Maps server+":"+export_name (see method Key()) to
+	 * #ManagedConnection.
+	 */
+	std::map<std::string, ManagedConnection> connections;
+
+public:
+	NfsManager(EventLoop &_loop)
+		:loop(_loop) {}
+
+	gcc_pure
+	NfsConnection &GetConnection(const char *server,
+				     const char *export_name);
+
+private:
+	gcc_pure
+	static std::string Key(const char *server, const char *export_name) {
+		return std::string(server) + ':' + export_name;
+	}
+};
+
+#endif