storage/nfs: optimize OpenFile()

src/lib/nfs/FileReader.cxx

@@ -10,6 +10,8 @@
 
 #include <nfsc/libnfs.h> // for struct nfs_stat_64
 
+#include <fmt/core.h>
+
 #include <cassert>
 #include <cstring>
 #include <stdexcept>
@@ -18,16 +20,37 @@
 #include <fcntl.h>
 #include <sys/stat.h> // for S_ISREG()
 
+using std::string_view_literals::operator""sv;
+
 NfsFileReader::NfsFileReader() noexcept
 	:defer_open(nfs_get_event_loop(), BIND_THIS_METHOD(OnDeferredOpen))
 {
 }
 
+NfsFileReader::NfsFileReader(NfsConnection &_connection,
+			     std::string_view _path) noexcept
+	:state(State::DEFER),
+	 path(_path),
+	 connection(&_connection),
+	 defer_open(_connection.GetEventLoop(), BIND_THIS_METHOD(OnDeferredOpen))
+{
+	defer_open.Schedule();
+}
+
 NfsFileReader::~NfsFileReader() noexcept
 {
 	assert(state == State::INITIAL);
 }
 
+std::string
+NfsFileReader::GetAbsoluteUri() const noexcept
+{
+	return fmt::format("nfs://{}{}/{}"sv,
+			   connection != nullptr ? connection->GetServer() : server,
+			   connection != nullptr ? connection->GetExportName() : export_name,
+			   path);
+}
+
 void
 NfsFileReader::Close() noexcept
 {
@@ -293,12 +316,13 @@ NfsFileReader::OnDeferredOpen() noexcept
 {
 	assert(state == State::DEFER);
 
-	try {
-		connection = &nfs_get_connection(server, export_name);
-	} catch (...) {
-		OnNfsFileError(std::current_exception());
-		return;
-	}
+	if (connection == nullptr)
+		try {
+			connection = &nfs_get_connection(server, export_name);
+		} catch (...) {
+			OnNfsFileError(std::current_exception());
+			return;
+		}
 
 	connection->AddLease(*this);
 	state = State::MOUNT;

src/lib/nfs/FileReader.hxx

@@ -45,7 +45,7 @@ class NfsFileReader : NfsLease, NfsCallback {
 
 	std::string server, export_name, path;
 
-	NfsConnection *connection;
+	NfsConnection *connection = nullptr;
 
 	nfsfh *fh;
 
@@ -60,12 +60,17 @@ class NfsFileReader : NfsLease, NfsCallback {
 
 public:
 	NfsFileReader() noexcept;
+	explicit NfsFileReader(NfsConnection &_connection,
+			       std::string_view _path) noexcept;
 	~NfsFileReader() noexcept;
 
 	auto &GetEventLoop() const noexcept {
 		return defer_open.GetEventLoop();
 	}
 
+	[[nodiscard]] [[gnu::pure]]
+	std::string GetAbsoluteUri() const noexcept;
+
 	void Close() noexcept;
 	void DeferClose() noexcept;