cherry pick "NFSv4.1 provide mount option to toggle trunking discovery"

we got lots of reports with QNAP NFS being broken, and the commit
this cherry picked one fixes got backported to 5.15 by canonical, so
its def. worth a try.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

patches/kernel/0013-NFSv4.1-provide-mount-option-to-toggle-trunking-disc.patch

@@ -0,0 +1,81 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Olga Kornievskaia <kolga@netapp.com>
+Date: Wed, 16 Mar 2022 18:24:26 -0400
+Subject: [PATCH] NFSv4.1 provide mount option to toggle trunking discovery
+
+Introduce a new mount option -- trunkdiscovery,notrunkdiscovery -- to
+toggle whether or not the client will engage in actively discovery
+of trunking locations.
+
+v2 make notrunkdiscovery default
+
+Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
+Fixes: 1976b2b31462 ("NFSv4.1 query for fs_location attr on a new file system")
+Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
+(cherry picked from commit a43bf604446414103b7535f38e739b65601c4fb2)
+Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
+---
+ fs/nfs/client.c           | 3 ++-
+ fs/nfs/fs_context.c       | 8 ++++++++
+ include/linux/nfs_fs_sb.h | 1 +
+ 3 files changed, 11 insertions(+), 1 deletion(-)
+
+diff --git a/fs/nfs/client.c b/fs/nfs/client.c
+index 090b16890e3d..f303e96ce165 100644
+--- a/fs/nfs/client.c
++++ b/fs/nfs/client.c
+@@ -861,7 +861,8 @@ int nfs_probe_fsinfo(struct nfs_server *server, struct nfs_fh *mntfh, struct nfs
+ 	}
+ 
+ 	if (clp->rpc_ops->discover_trunking != NULL &&
+-			(server->caps & NFS_CAP_FS_LOCATIONS)) {
++			(server->caps & NFS_CAP_FS_LOCATIONS &&
++			 (server->flags & NFS_MOUNT_TRUNK_DISCOVERY))) {
+ 		error = clp->rpc_ops->discover_trunking(server, mntfh);
+ 		if (error < 0)
+ 			return error;
+diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
+index 0d444a90f513..da5217abc2e5 100644
+--- a/fs/nfs/fs_context.c
++++ b/fs/nfs/fs_context.c
+@@ -79,6 +79,7 @@ enum nfs_param {
+ 	Opt_source,
+ 	Opt_tcp,
+ 	Opt_timeo,
++	Opt_trunkdiscovery,
+ 	Opt_udp,
+ 	Opt_v,
+ 	Opt_vers,
+@@ -179,6 +180,7 @@ static const struct fs_parameter_spec nfs_fs_parameters[] = {
+ 	fsparam_string("source",	Opt_source),
+ 	fsparam_flag  ("tcp",		Opt_tcp),
+ 	fsparam_u32   ("timeo",		Opt_timeo),
++	fsparam_flag_no("trunkdiscovery", Opt_trunkdiscovery),
+ 	fsparam_flag  ("udp",		Opt_udp),
+ 	fsparam_flag  ("v2",		Opt_v),
+ 	fsparam_flag  ("v3",		Opt_v),
+@@ -528,6 +530,12 @@ static int nfs_fs_context_parse_param(struct fs_context *fc,
+ 		else
+ 			ctx->flags &= ~NFS_MOUNT_NOCTO;
+ 		break;
++	case Opt_trunkdiscovery:
++		if (result.negated)
++			ctx->flags &= ~NFS_MOUNT_TRUNK_DISCOVERY;
++		else
++			ctx->flags |= NFS_MOUNT_TRUNK_DISCOVERY;
++		break;
+ 	case Opt_ac:
+ 		if (result.negated)
+ 			ctx->flags |= NFS_MOUNT_NOAC;
+diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
+index 9a6e70ccde56..10c347416dd2 100644
+--- a/include/linux/nfs_fs_sb.h
++++ b/include/linux/nfs_fs_sb.h
+@@ -156,6 +156,7 @@ struct nfs_server {
+ #define NFS_MOUNT_SOFTREVAL		0x800000
+ #define NFS_MOUNT_WRITE_EAGER		0x01000000
+ #define NFS_MOUNT_WRITE_WAIT		0x02000000
++#define NFS_MOUNT_TRUNK_DISCOVERY	0x04000000
+ 
+ 	unsigned int		fattr_valid;	/* Valid attributes */
+ 	unsigned int		caps;		/* server capabilities */