lockd: add a /proc/fs/lockd/nlm_end_grace file

Add a new procfile that will allow a (privileged) userland process to
end the NLM grace period early. The basic idea here will be to have
sm-notify write to this file, if it sent out no NOTIFY requests when
it runs. In that situation, we can generally expect that there will be
no reclaim requests so the grace period can be lifted early.

Signed-off-by: Jeff Layton <[e-mail]>

fs/lockd/Makefile

···
 lockd-objs-y := clntlock.o clntproc.o clntxdr.o host.o svc.o svclock.o \
 	        svcshare.o svcproc.o svcsubs.o mon.o xdr.o
 lockd-objs-$(CONFIG_LOCKD_V4) += clnt4xdr.o xdr4.o svc4proc.o
+lockd-objs-$(CONFIG_PROC_FS) += procfs.o
 lockd-objs		      := $(lockd-objs-y)

fs/lockd/procfs.c

···
+/*
+ * Procfs support for lockd
+ *
+ * Copyright (c) 2014 Jeff Layton <[e-mail]>
+ */
+
+#include <linux/fs.h>
+#include <linux/proc_fs.h>
+#include <linux/module.h>
+#include <linux/nsproxy.h>
+#include <net/net_namespace.h>
+
+#include "netns.h"
+#include "procfs.h"
+
+/*
+ * We only allow strings that start with 'Y', 'y', or '1'.
+ */
+static ssize_t
+nlm_end_grace_write(struct file *file, const char __user *buf, size_t size,
+		    loff_t *pos)
+{
+	char *data;
+	struct lockd_net *ln = net_generic(current->nsproxy->net_ns,
+					   lockd_net_id);
+
+	if (size < 1)
+		return -EINVAL;
+
+	data = simple_transaction_get(file, buf, size);
+	if (IS_ERR(data))
+		return PTR_ERR(data);
+
+	switch(data[0]) {
+	case 'Y':
+	case 'y':
+	case '1':
+		locks_end_grace(&ln->lockd_manager);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return size;
+}
+
+static ssize_t
+nlm_end_grace_read(struct file *file, char __user *buf, size_t size,
+		   loff_t *pos)
+{
+	struct lockd_net *ln = net_generic(current->nsproxy->net_ns,
+					   lockd_net_id);
+	char resp[3];
+
+	resp[0] = list_empty(&ln->lockd_manager.list) ? 'Y' : 'N';
+	resp[1] = '\n';
+	resp[2] = '\0';
+
+	return simple_read_from_buffer(buf, size, pos, resp, sizeof(resp));
+}
+
+static const struct file_operations lockd_end_grace_operations = {
+	.write		= nlm_end_grace_write,
+	.read		= nlm_end_grace_read,
+	.llseek		= default_llseek,
+	.release	= simple_transaction_release,
+	.owner		= THIS_MODULE,
+};
+
+int __init
+lockd_create_procfs(void)
+{
+	struct proc_dir_entry *entry;
+
+	entry = proc_mkdir("fs/lockd", NULL);
+	if (!entry)
+		return -ENOMEM;
+	entry = proc_create("nlm_end_grace", S_IRUGO|S_IWUSR, entry,
+				 &lockd_end_grace_operations);
+	if (!entry) {
+		remove_proc_entry("fs/lockd", NULL);
+		return -ENOMEM;
+	}
+	return 0;
+}
+
+void __exit
+lockd_remove_procfs(void)
+{
+	remove_proc_entry("fs/lockd/nlm_end_grace", NULL);
+	remove_proc_entry("fs/lockd", NULL);
+}

fs/lockd/procfs.h

···
+/*
+ * Procfs support for lockd
+ *
+ * Copyright (c) 2014 Jeff Layton <[e-mail]>
+ */
+#ifndef _LOCKD_PROCFS_H
+#define _LOCKD_PROCFS_H
+
+#include <linux/kconfig.h>
+
+#if IS_ENABLED(CONFIG_PROC_FS)
+int lockd_create_procfs(void);
+void lockd_remove_procfs(void);
+#else
+static inline int
+lockd_create_procfs(void)
+{
+	return 0;
+}
+
+static inline void
+lockd_remove_procfs(void)
+{
+	return;
+}
+#endif /* IS_ENABLED(CONFIG_PROC_FS) */
+
+#endif /* _LOCKD_PROCFS_H */

fs/lockd/svc.c

···
 #include <linux/nfs.h>
 
 #include "netns.h"
+#include "procfs.h"
 
 #define NLMDBG_FACILITY		NLMDBG_SVC
 #define LOCKD_BUFSIZE		(1024 + NLMSVC_XDRSIZE)
···
 	err = register_pernet_subsys(&lockd_net_ops);
 	if (err)
 		goto err_pernet;
+
+	err = lockd_create_procfs();
+	if (err)
+		goto err_procfs;
+
 	return 0;
 
+err_procfs:
+	unregister_pernet_subsys(&lockd_net_ops);
 err_pernet:
 #ifdef CONFIG_SYSCTL
 	unregister_sysctl_table(nlm_sysctl_table);
···
 {
 	/* FIXME: delete all NLM clients */
 	nlm_shutdown_hosts();
+	lockd_remove_procfs();
 	unregister_pernet_subsys(&lockd_net_ops);
 #ifdef CONFIG_SYSCTL
 	unregister_sysctl_table(nlm_sysctl_table);