lib/nfs/Base: kludge to reduce number of NFS mounts

Creating a NfsStorage sets its own export_name as the "base".  Now
NfsFileReader can use this information to derive the export_name to be
mounted, instead of guessing.  This solves the "too many connection"
problem on the NFS server while updating the database.

Makefile.am

@@ -559,6 +559,7 @@ NFS_SOURCES = \
 	src/lib/nfs/Connection.cxx src/lib/nfs/Connection.hxx \
 	src/lib/nfs/Manager.cxx src/lib/nfs/Manager.hxx \
 	src/lib/nfs/Glue.cxx src/lib/nfs/Glue.hxx \
+	src/lib/nfs/Base.cxx src/lib/nfs/Base.hxx \
 	src/lib/nfs/FileReader.cxx src/lib/nfs/FileReader.hxx \
 	src/lib/nfs/Domain.cxx src/lib/nfs/Domain.hxx
 

src/lib/nfs/Base.cxx

@@ -0,0 +1,61 @@
+/*
+ * 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 "Base.hxx"
+
+#include <assert.h>
+#include <string.h>
+
+static char nfs_base_server[64];
+static char nfs_base_export_name[256];
+static size_t nfs_base_export_name_length;
+
+void
+nfs_set_base(const char *server, const char *export_name)
+{
+	assert(server != nullptr);
+	assert(export_name != nullptr);
+
+	const size_t server_length = strlen(server);
+	const size_t export_name_length = strlen(export_name);
+
+	if (server_length >= sizeof(nfs_base_server) ||
+	    export_name_length > sizeof(nfs_base_export_name))
+		return;
+
+	memcpy(nfs_base_server, server, server_length + 1);
+	memcpy(nfs_base_export_name, export_name, export_name_length);
+	nfs_base_export_name_length = export_name_length;
+}
+
+const char *
+nfs_check_base(const char *server, const char *path)
+{
+	assert(server != nullptr);
+	assert(path != nullptr);
+
+	return strcmp(nfs_base_server, server) == 0 &&
+	    memcmp(nfs_base_export_name, path,
+		   nfs_base_export_name_length) == 0 &&
+		(path[nfs_base_export_name_length] == 0 ||
+		 path[nfs_base_export_name_length] == '/')
+		? path + nfs_base_export_name_length
+		: nullptr;
+}

src/lib/nfs/Base.hxx

@@ -0,0 +1,46 @@
+/*
+ * 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_BASE_HXX
+#define MPD_NFS_BASE_HXX
+
+#include "check.h"
+#include "Compiler.h"
+
+/**
+ * Set the "base" NFS server and export name.  This will be the
+ * default export that will be mounted if a file within this export is
+ * being opened, instead of guessing the mount point.
+ *
+ * This is a kludge that is not truly thread-safe.
+ */
+void
+nfs_set_base(const char *server, const char *export_name);
+
+/**
+ * Check if the given server and path are inside the "base"
+ * server/export_name.  If yes, then a pointer to the portion of
+ * "path" after the export_name is returned; otherwise, nullptr is
+ * returned.
+ */
+gcc_pure
+const char *
+nfs_check_base(const char *server, const char *path);
+
+#endif

src/lib/nfs/FileReader.cxx

@@ -20,6 +20,7 @@
 #include "config.h"
 #include "FileReader.hxx"
 #include "Glue.hxx"
+#include "Base.hxx"
 #include "Connection.hxx"
 #include "Domain.hxx"
 #include "event/Call.hxx"
@@ -100,14 +101,23 @@ NfsFileReader::Open(const char *uri, Error &error)
 	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;
+	const char *new_path = nfs_check_base(server.c_str(), uri);
+	if (new_path != nullptr) {
+		export_name = std::string(uri, new_path);
+		if (*new_path == 0)
+			new_path = "/";
+		path = new_path;
+	} else {
+		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();

src/storage/plugins/NfsStorage.cxx

@@ -23,6 +23,7 @@
 #include "storage/StorageInterface.hxx"
 #include "storage/FileInfo.hxx"
 #include "lib/nfs/Domain.hxx"
+#include "lib/nfs/Base.hxx"
 #include "fs/AllocatedPath.hxx"
 #include "util/Error.hxx"
 #include "thread/Mutex.hxx"
@@ -256,6 +257,8 @@ CreateNfsStorageURI(const char *base, Error &error)
 		return nullptr;
 	}
 
+	nfs_set_base(server.c_str(), mount);
+
 	return new NfsStorage(base, ctx);
 }