NFS: Extend rdirplus mount option with "force|none"

There are certain users that wish to force the NFS client to choose
READDIRPLUS over READDIR for a particular mount.  Update the "rdirplus" mount
option to optionally accept values.  For "rdirplus=force", the NFS client
will always attempt to use READDDIRPLUS.  The setting of "rdirplus=none" is
aliased to the existing "nordirplus".

Signed-off-by: Benjamin Coddington <[email protected]>
Link: https://lore.kernel.org/r/c4cf0de4c8be0930b91bc74bee310d289781cd3b.1741885071.git.bcodding@redhat.com
Signed-off-by: Trond Myklebust <[email protected]>

Author: bcodding-rh

fs/nfs/dir.c

@@ -666,6 +666,8 @@ static bool nfs_use_readdirplus(struct inode *dir, struct dir_context *ctx,
 {
 	if (!nfs_server_capable(dir, NFS_CAP_READDIRPLUS))
 		return false;
+	if (NFS_SERVER(dir)->flags & NFS_MOUNT_FORCE_RDIRPLUS)
+		return true;
 	if (ctx->pos == 0 ||
 	    cache_hits + cache_misses > NFS_READDIR_CACHE_USAGE_THRESHOLD)
 		return true;

fs/nfs/fs_context.c

@@ -72,6 +72,8 @@ enum nfs_param {
 	Opt_posix,
 	Opt_proto,
 	Opt_rdirplus,
+	Opt_rdirplus_none,
+	Opt_rdirplus_force,
 	Opt_rdma,
 	Opt_resvport,
 	Opt_retrans,
@@ -174,7 +176,8 @@ static const struct fs_parameter_spec nfs_fs_parameters[] = {
 	fsparam_u32   ("port",		Opt_port),
 	fsparam_flag_no("posix",	Opt_posix),
 	fsparam_string("proto",		Opt_proto),
-	fsparam_flag_no("rdirplus",	Opt_rdirplus),
+	fsparam_flag_no("rdirplus", Opt_rdirplus), // rdirplus|nordirplus
+	fsparam_string("rdirplus",  Opt_rdirplus), // rdirplus=...
 	fsparam_flag  ("rdma",		Opt_rdma),
 	fsparam_flag_no("resvport",	Opt_resvport),
 	fsparam_u32   ("retrans",	Opt_retrans),
@@ -288,6 +291,12 @@ static const struct constant_table nfs_xprtsec_policies[] = {
 	{}
 };
 
+static const struct constant_table nfs_rdirplus_tokens[] = {
+	{ "none",	Opt_rdirplus_none },
+	{ "force",	Opt_rdirplus_force },
+	{}
+};
+
 /*
  * Sanity-check a server address provided by the mount command.
  *
@@ -636,10 +645,25 @@ static int nfs_fs_context_parse_param(struct fs_context *fc,
 			ctx->flags &= ~NFS_MOUNT_NOACL;
 		break;
 	case Opt_rdirplus:
-		if (result.negated)
+		if (result.negated) {
+			ctx->flags &= ~NFS_MOUNT_FORCE_RDIRPLUS;
 			ctx->flags |= NFS_MOUNT_NORDIRPLUS;
-		else
-			ctx->flags &= ~NFS_MOUNT_NORDIRPLUS;
+		} else if (!param->string) {
+			ctx->flags &= ~(NFS_MOUNT_NORDIRPLUS | NFS_MOUNT_FORCE_RDIRPLUS);
+		} else {
+			switch (lookup_constant(nfs_rdirplus_tokens, param->string, -1)) {
+			case Opt_rdirplus_none:
+				ctx->flags &= ~NFS_MOUNT_FORCE_RDIRPLUS;
+				ctx->flags |= NFS_MOUNT_NORDIRPLUS;
+				break;
+			case Opt_rdirplus_force:
+				ctx->flags &= ~NFS_MOUNT_NORDIRPLUS;
+				ctx->flags |= NFS_MOUNT_FORCE_RDIRPLUS;
+				break;
+			default:
+				goto out_invalid_value;
+			}
+		}
 		break;
 	case Opt_sharecache:
 		if (result.negated)

fs/nfs/super.c

@@ -454,6 +454,7 @@ static void nfs_show_mount_options(struct seq_file *m, struct nfs_server *nfss,
 		{ NFS_MOUNT_NONLM, ",nolock", "" },
 		{ NFS_MOUNT_NOACL, ",noacl", "" },
 		{ NFS_MOUNT_NORDIRPLUS, ",nordirplus", "" },
+		{ NFS_MOUNT_FORCE_RDIRPLUS, ",rdirplus=force", "" },
 		{ NFS_MOUNT_UNSHARED, ",nosharecache", "" },
 		{ NFS_MOUNT_NORESVPORT, ",noresvport", "" },
 		{ 0, NULL, NULL }

include/linux/nfs_fs_sb.h

@@ -167,6 +167,7 @@ struct nfs_server {
 #define NFS_MOUNT_TRUNK_DISCOVERY	0x04000000
 #define NFS_MOUNT_SHUTDOWN			0x08000000
 #define NFS_MOUNT_NO_ALIGNWRITE		0x10000000
+#define NFS_MOUNT_FORCE_RDIRPLUS	0x20000000
 
 	unsigned int		fattr_valid;	/* Valid attributes */
 	unsigned int		caps;		/* server capabilities */