[kernel RFC PATCH 2/4] nfsd: add a v4_end_grace file to /proc/fs/nfsd

[Jeff Layton <jlayton@primarydata.com>]

Allow a privileged userland process to end the v4 grace period early.
Any write to the file will cause the v4 grace period to be lifted.

The basic idea with this will be to allow the userland client tracking
program to lift the grace period once it knows that no more clients
will be reclaiming state.

Signed-off-by: Jeff Layton <jlayton@primarydata.com>
---
 fs/nfsd/nfs4state.c |  2 +-
 fs/nfsd/nfsctl.c    | 35 +++++++++++++++++++++++++++++++++++
 fs/nfsd/state.h     |  3 +++
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 5c5873811bd9..de6bea769b24 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -4123,7 +4123,7 @@ out:
 	return status;
 }
 
-static void
+void
 nfsd4_end_grace(struct nfsd_net *nn)
 {
 	/* do nothing if grace period already ended */
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 4e042105fb6e..99044e237861 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -49,6 +49,7 @@ enum {
 	NFSD_Leasetime,
 	NFSD_Gracetime,
 	NFSD_RecoveryDir,
+	NFSD_V4EndGrace,
 #endif
 };
 
@@ -68,6 +69,7 @@ static ssize_t write_maxconn(struct file *file, char *buf, size_t size);
 static ssize_t write_leasetime(struct file *file, char *buf, size_t size);
 static ssize_t write_gracetime(struct file *file, char *buf, size_t size);
 static ssize_t write_recoverydir(struct file *file, char *buf, size_t size);
+static ssize_t write_v4_end_grace(struct file *file, char *buf, size_t size);
 #endif
 
 static ssize_t (*write_op[])(struct file *, char *, size_t) = {
@@ -84,6 +86,7 @@ static ssize_t (*write_op[])(struct file *, char *, size_t) = {
 	[NFSD_Leasetime] = write_leasetime,
 	[NFSD_Gracetime] = write_gracetime,
 	[NFSD_RecoveryDir] = write_recoverydir,
+	[NFSD_V4EndGrace] = write_v4_end_grace,
 #endif
 };
 
@@ -1077,6 +1080,37 @@ static ssize_t write_recoverydir(struct file *file, char *buf, size_t size)
 	return rv;
 }
 
+/**
+ * write_v4_end_grace - release grace period for nfsd's v4.x lock manager
+ *
+ * Input:
+ *			buf:		ignored
+ *			size:		zero
+ * OR
+ *
+ * Input:
+ * 			buf:		any value
+ *			size:		non-zero length of C string in @buf
+ * Output:
+ *			passed-in buffer filled with "Y" or "N" with a newline
+ *			and NULL-terminated C string. This indicates whether
+ *			the grace period has ended in the current net
+ *			namespace. Return code is the size in bytes of the
+ *			string. Writing to the file will end the grace period
+ *			for nfsd's v4 lock manager.
+ */
+static ssize_t write_v4_end_grace(struct file *file, char *buf, size_t size)
+{
+	struct net *net = file->f_dentry->d_sb->s_fs_info;
+	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+
+	if (size > 0)
+		nfsd4_end_grace(nn);
+
+	return scnprintf(buf, SIMPLE_TRANSACTION_LIMIT, "%c\n",
+			 nn->grace_ended ? 'Y' : 'N');
+}
+
 #endif
 
 /*----------------------------------------------------------------------------*/
@@ -1110,6 +1144,7 @@ static int nfsd_fill_super(struct super_block * sb, void * data, int silent)
 		[NFSD_Leasetime] = {"nfsv4leasetime", &transaction_ops, S_IWUSR|S_IRUSR},
 		[NFSD_Gracetime] = {"nfsv4gracetime", &transaction_ops, S_IWUSR|S_IRUSR},
 		[NFSD_RecoveryDir] = {"nfsv4recoverydir", &transaction_ops, S_IWUSR|S_IRUSR},
+		[NFSD_V4EndGrace] = {"v4_end_grace", &transaction_ops, S_IWUSR|S_IRUGO},
 #endif
 		/* last one */ {""}
 	};
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 4a89e00d7461..ecf579904892 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -545,6 +545,9 @@ extern struct nfs4_client_reclaim *nfs4_client_to_reclaim(const char *name,
 							struct nfsd_net *nn);
 extern bool nfs4_has_reclaimed_state(const char *name, struct nfsd_net *nn);
 
+/* grace period management */
+void nfsd4_end_grace(struct nfsd_net *nn);
+
 /* nfs4recover operations */
 extern int nfsd4_client_tracking_init(struct net *net);
 extern void nfsd4_client_tracking_exit(struct net *net);
-- 
1.9.3