[PATCH 7/7] NFS: Add a mount option for READ_PLUS

[schumaker.anna@gmail.com]

From: Anna Schumaker <Anna.Schumaker@Netapp.com>

There are some workloads where READ_PLUS might end up hurting
performance, so let's be nice to users and provide a way to disable this
operation similar to how READDIR_PLUS can be disabled.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
---
 fs/nfs/fs_context.c       | 14 ++++++++++++++
 fs/nfs/nfs4client.c       |  3 +++
 include/linux/nfs_fs_sb.h |  1 +
 3 files changed, 18 insertions(+)

diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
index 0247dcb7b316..82ba07c7c1ce 100644
--- a/fs/nfs/fs_context.c
+++ b/fs/nfs/fs_context.c
@@ -64,6 +64,7 @@ enum nfs_param {
 	Opt_proto,
 	Opt_rdirplus,
 	Opt_rdma,
+	Opt_readplus,
 	Opt_resvport,
 	Opt_retrans,
 	Opt_retry,
@@ -120,6 +121,7 @@ static const struct fs_parameter_spec nfs_param_specs[] = {
 	fsparam_string("proto",		Opt_proto),
 	fsparam_flag_no("rdirplus",	Opt_rdirplus),
 	fsparam_flag  ("rdma",		Opt_rdma),
+	fsparam_flag_no("readplus",	Opt_readplus),
 	fsparam_flag_no("resvport",	Opt_resvport),
 	fsparam_u32   ("retrans",	Opt_retrans),
 	fsparam_string("retry",		Opt_retry),
@@ -555,6 +557,12 @@ static int nfs_fs_context_parse_param(struct fs_context *fc,
 		else
 			ctx->options |= NFS_OPTION_MIGRATION;
 		break;
+	case Opt_readplus:
+		if (result.negated)
+			ctx->options |= NFS_OPTION_NO_READ_PLUS;
+		else
+			ctx->options &= ~NFS_OPTION_NO_READ_PLUS;
+		break;
 
 		/*
 		 * options that take numeric values
@@ -1176,6 +1184,10 @@ static int nfs_fs_context_validate(struct fs_context *fc)
 	    (ctx->version != 4 || ctx->minorversion != 0))
 		goto out_migration_misuse;
 
+	if (ctx->options & NFS_OPTION_NO_READ_PLUS &&
+	    (ctx->version != 4 || ctx->minorversion < 2))
+		goto out_noreadplus_misuse;
+
 	/* Verify that any proto=/mountproto= options match the address
 	 * families in the addr=/mountaddr= options.
 	 */
@@ -1254,6 +1266,8 @@ static int nfs_fs_context_validate(struct fs_context *fc)
 			  ctx->version, ctx->minorversion);
 out_migration_misuse:
 	return nfs_invalf(fc, "NFS: 'Migration' not supported for this NFS version");
+out_noreadplus_misuse:
+	return nfs_invalf(fc, "NFS: 'noreadplus' not supported for this NFS version\n");
 out_version_unavailable:
 	nfs_errorf(fc, "NFS: Version unavailable");
 	return ret;
diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
index 0cd767e5c977..868dc3c36ba1 100644
--- a/fs/nfs/nfs4client.c
+++ b/fs/nfs/nfs4client.c
@@ -1016,6 +1016,9 @@ static int nfs4_server_common_setup(struct nfs_server *server,
 	server->caps |= server->nfs_client->cl_mvops->init_caps;
 	if (server->flags & NFS_MOUNT_NORDIRPLUS)
 			server->caps &= ~NFS_CAP_READDIRPLUS;
+	if (server->options & NFS_OPTION_NO_READ_PLUS)
+		server->caps &= ~NFS_CAP_READ_PLUS;
+
 	/*
 	 * Don't use NFS uid/gid mapping if we're using AUTH_SYS or lower
 	 * authentication.
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index 11248c5a7b24..360e70c7bbb6 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -172,6 +172,7 @@ struct nfs_server {
 	unsigned int		clone_blksize;	/* granularity of a CLONE operation */
 #define NFS_OPTION_FSCACHE	0x00000001	/* - local caching enabled */
 #define NFS_OPTION_MIGRATION	0x00000002	/* - NFSv4 migration enabled */
+#define NFS_OPTION_NO_READ_PLUS	0x00000004	/* - NFSv4.2 READ_PLUS enabled */
 
 	struct nfs_fsid		fsid;
 	__u64			maxfilesize;	/* maximum file size */
-- 
2.24.1