lib/nfs: initial support for libnfs API 2

Commit
sahlberg/libnfs@5e8f7ce
introduced the libnfs API version 2 which may eventually become libnfs
version 6.

This version detection depends on my pull request
sahlberg/libnfs#468

NEWS

@@ -26,6 +26,7 @@ ver 0.24 (not yet released)
 * storage
   - curl: optimize database update
   - nfs: require libnfs 4.0 or later
+  - nfs: support libnfs 6 (API version 2)
   - nfs: support libnfs URL arguments
 * input
   - alsa: limit ALSA buffer time to 2 seconds

src/lib/nfs/Connection.cxx

@@ -81,11 +81,25 @@ NfsConnection::CancellableCallback::Stat(nfs_context *ctx,
 
 inline void
 NfsConnection::CancellableCallback::Read(nfs_context *ctx, struct nfsfh *fh,
-					 uint64_t offset, size_t size)
+					 uint64_t offset,
+#ifdef LIBNFS_API_2
+					 std::span<std::byte> dest
+#else
+					 std::size_t size
+#endif
+	)
 {
 	assert(connection.GetEventLoop().IsInside());
 
-	int result = nfs_pread_async(ctx, fh, offset, size, Callback, this);
+	int result = nfs_pread_async(ctx, fh,
+#ifdef LIBNFS_API_2
+				     dest.data(), dest.size(),
+#endif
+				     offset,
+#ifndef LIBNFS_API_2
+				     size,
+#endif
+				     Callback, this);
 	if (result < 0)
 		throw NfsClientError(ctx, "nfs_pread_async() failed");
 }
@@ -328,15 +342,26 @@ NfsConnection::Stat(struct nfsfh *fh, NfsCallback &callback)
 }
 
 void
-NfsConnection::Read(struct nfsfh *fh, uint64_t offset, size_t size,
+NfsConnection::Read(struct nfsfh *fh, uint64_t offset,
+#ifdef LIBNFS_API_2
+		    std::span<std::byte> dest,
+#else
+		    std::size_t size,
+#endif
 		    NfsCallback &callback)
 {
 	assert(GetEventLoop().IsInside());
 	assert(!callbacks.Contains(callback));
 
 	auto &c = callbacks.Add(callback, *this, false);
 	try {
-		c.Read(context, fh, offset, size);
+		c.Read(context, fh, offset,
+#ifdef LIBNFS_API_2
+		       dest
+#else
+		       size
+#endif
+			);
 	} catch (...) {
 		callbacks.Remove(c);
 		throw;

src/lib/nfs/Connection.hxx

@@ -62,7 +62,13 @@ class NfsConnection {
 		void Open(nfs_context *context, const char *path, int flags);
 		void Stat(nfs_context *context, struct nfsfh *fh);
 		void Read(nfs_context *context, struct nfsfh *fh,
-			  uint64_t offset, size_t size);
+			  uint64_t offset,
+#ifdef LIBNFS_API_2
+			  std::span<std::byte> dest
+#else
+			  std::size_t size
+#endif
+			);
 
 		/**
 		 * Cancel the operation and schedule a call to
@@ -210,7 +216,12 @@ public:
 	/**
 	 * Throws on error.
 	 */
-	void Read(struct nfsfh *fh, uint64_t offset, size_t size,
+	void Read(struct nfsfh *fh, uint64_t offset,
+#ifdef LIBNFS_API_2
+		  std::span<std::byte> dest,
+#else
+		  std::size_t size,
+#endif
 		  NfsCallback &callback);
 
 	/**

src/lib/nfs/FileReader.cxx

@@ -59,7 +59,13 @@ NfsFileReader::CancelOrClose() noexcept
 	else if (state > State::OPEN)
 		/* one async operation in progress: cancel it and
 		   defer the nfs_close_async() call */
-		connection->CancelAndClose(fh, {}, *this);
+		connection->CancelAndClose(fh,
+#ifdef LIBNFS_API_2
+					   ToDeleteArray(read_buffer.release()),
+#else
+					   {},
+#endif
+					   *this);
 	else if (state > State::MOUNT)
 		/* we don't have a file handle yet - just cancel the
 		   async operation */
@@ -116,7 +122,15 @@ NfsFileReader::Read(uint64_t offset, size_t size)
 {
 	assert(state == State::IDLE);
 
+#ifdef LIBNFS_API_2
+	assert(!read_buffer);
+	// TOOD read into caller-provided buffer
+	read_buffer = std::make_unique<std::byte[]>(size);
+	connection->Read(fh, offset, {read_buffer.get(), size}, *this);
+#else
 	connection->Read(fh, offset, size, *this);
+#endif
+
 	state = State::READ;
 }
 
@@ -200,7 +214,16 @@ NfsFileReader::StatCallback(const struct nfs_stat_64 *st) noexcept
 inline void
 NfsFileReader::ReadCallback(std::size_t nbytes, const void *data) noexcept
 {
+#ifdef LIBNFS_API_2
+	(void)data;
+
+	assert(read_buffer);
+	const auto buffer = std::move(read_buffer);
+
+	OnNfsFileRead({buffer.get(), nbytes});
+#else
 	OnNfsFileRead({static_cast<const std::byte *>(data), nbytes});
+#endif
 }
 
 void

src/lib/nfs/FileReader.hxx

@@ -14,6 +14,10 @@
 #include <span>
 #include <string>
 
+#ifdef LIBNFS_API_2
+#include <memory>
+#endif
+
 struct nfsfh;
 struct nfs_stat_64;
 class NfsConnection;
@@ -51,6 +55,10 @@ class NfsFileReader : NfsLease, NfsCallback {
 	 */
 	InjectEvent defer_open;
 
+#ifdef LIBNFS_API_2
+	std::unique_ptr<std::byte[]> read_buffer;
+#endif
+
 public:
 	NfsFileReader() noexcept;
 	~NfsFileReader() noexcept;

src/lib/nfs/meson.build

@@ -4,6 +4,13 @@ if not nfs_dep.found()
   subdir_done()
 endif
 
+if nfs_dep.version().version_compare('>=6')
+  # libnfs has no version macro therefore we must detect the API
+  # version 2 at configure time
+  nfs_dep = declare_dependency(compile_args: '-DLIBNFS_API_2',
+                               dependencies: nfs_dep)
+endif
+
 nfs = static_library(
   'nfs',
   'Connection.cxx',