Store nfs v4 url extensions in state file

[skidoo23]

Store nfs v4 url extensions in MPD state file. Add via nfs v4 exported directory to MPD (without version=4 mount is not successful) MPD and mpc from git. Compiled to Debian testing x64.

$ mpc mount nfs 'nfs://nfs:/data/music?version=4'

Now access to audio files unter nfs is possible. MPD statefile now shows

uri: nfs
mounted_url: nfs://nfs/data/music
mount_end

Restart MPD. Nfs directory does not work. Have to unmount and re-mount it again. Storage plugin supports url extensions for nfs https://mpd.readthedocs.io/en/latest/plugins.html#nfs - would be nice to have a consistent usage with input plugin.

[skidoo23]

Quick and dirty fix: force NFS v4 (no need to use URL extension)

$ mpc mount nfs 'nfs://nfs:/data/music'

diff --git a/src/lib/nfs/Connection.cxx b/src/lib/nfs/Connection.cxx
index 1901d43f2..b099d4faa 100644
--- a/src/lib/nfs/Connection.cxx
+++ b/src/lib/nfs/Connection.cxx
@@ -10,6 +10,7 @@

 extern "C" {
 #include <nfsc/libnfs.h>
+#include <nfsc/libnfs-raw-nfs4.h>
 }

 #include <utility>
@@ -200,6 +201,7 @@ NfsConnection::NfsConnection(EventLoop &_loop,
         server(_server), export_name(_export_name),
         context(_context)
 {
+       nfs_set_version(_context, NFS_V4);
 }

 NfsConnection::~NfsConnection() noexcept

Ugly but MPD works as advertised together with my NFS server. Correct solution: MPD should write NFS url extensions to state file and not to cache filename. I'm a little confused about how MPD creates and saves NFS url. Maybe someone could help?