[RFC PATCH 1/2] NFSD: Add /sys/kernel/debug/nfsd

[cel@kernel.org]

From: Chuck Lever <chuck.lever@oracle.com>

Create a small sandbox under /sys/kernel/debug for experimental NFS
server feature settings. There is no API/ABI compatibility guarantee
for these settings.

The only documentation for such settings, if any documentation exists,
is in the kernel source code.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/Makefile  |  1 +
 fs/nfsd/debugfs.c | 18 ++++++++++++++++++
 fs/nfsd/nfsctl.c  |  4 ++++
 fs/nfsd/nfsd.h    |  8 ++++++++
 4 files changed, 31 insertions(+)
 create mode 100644 fs/nfsd/debugfs.c

diff --git a/fs/nfsd/Makefile b/fs/nfsd/Makefile
index 2f687619f65b..55744bb786c9 100644
--- a/fs/nfsd/Makefile
+++ b/fs/nfsd/Makefile
@@ -24,6 +24,7 @@ nfsd-$(CONFIG_NFSD_BLOCKLAYOUT) += blocklayout.o blocklayoutxdr.o
 nfsd-$(CONFIG_NFSD_SCSILAYOUT) += blocklayout.o blocklayoutxdr.o
 nfsd-$(CONFIG_NFSD_FLEXFILELAYOUT) += flexfilelayout.o flexfilelayoutxdr.o
 nfsd-$(CONFIG_NFS_LOCALIO) += localio.o
+nfsd-$(CONFIG_DEBUG_FS) += debugfs.o
 
 
 .PHONY: xdrgen
diff --git a/fs/nfsd/debugfs.c b/fs/nfsd/debugfs.c
new file mode 100644
index 000000000000..e913268d9c2d
--- /dev/null
+++ b/fs/nfsd/debugfs.c
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/debugfs.h>
+
+#include "nfsd.h"
+
+static struct dentry *nfsd_top_dir __read_mostly;
+
+void nfsd_debugfs_exit(void)
+{
+	debugfs_remove_recursive(nfsd_top_dir);
+	nfsd_top_dir = NULL;
+}
+
+void nfsd_debugfs_init(void)
+{
+	nfsd_top_dir = debugfs_create_dir("nfsd", NULL);
+}
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index ce2a71e4904c..1919eafe500a 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -2276,6 +2276,8 @@ static int __init init_nfsd(void)
 {
 	int retval;
 
+	nfsd_debugfs_init();
+
 	retval = nfsd4_init_slabs();
 	if (retval)
 		return retval;
@@ -2323,6 +2325,7 @@ static int __init init_nfsd(void)
 	nfsd4_exit_pnfs();
 out_free_slabs:
 	nfsd4_free_slabs();
+	nfsd_debugfs_exit();
 	return retval;
 }
 
@@ -2339,6 +2342,7 @@ static void __exit exit_nfsd(void)
 	nfsd_lockd_shutdown();
 	nfsd4_free_slabs();
 	nfsd4_exit_pnfs();
+	nfsd_debugfs_exit();
 }
 
 MODULE_AUTHOR("Olaf Kirch <okir@monad.swb.de>");
diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
index e2997f0ffbc5..8a53ddab5df0 100644
--- a/fs/nfsd/nfsd.h
+++ b/fs/nfsd/nfsd.h
@@ -156,6 +156,14 @@ void nfsd_reset_versions(struct nfsd_net *nn);
 int nfsd_create_serv(struct net *net);
 void nfsd_destroy_serv(struct net *net);
 
+#ifdef CONFIG_DEBUG_FS
+void nfsd_debugfs_init(void);
+void nfsd_debugfs_exit(void);
+#else
+static inline void nfsd_debugfs_init(void) {}
+static inline void nfsd_debugfs_exit(void) {}
+#endif
+
 extern int nfsd_max_blksize;
 
 static inline int nfsd_v4client(struct svc_rqst *rq)
-- 
2.48.1