[PATCH 3/9] NFS: add superblock sysfs entries

[Benjamin Coddington <bcodding@redhat.com>]

Create a sysfs directory for each mount that corresponds to the mount's
nfs_server struct.  As the mount is being constructed, use the name
"server-n", but rename it to the "MAJOR:MINOR" of the mount after assigning
a device_id. The rename approach allows us to populate the mount's directory
with links to the various rpc_client objects during the mount's
construction.  The naming convention (MAJOR:MINOR) can be used to reference
a particular NFS mount's sysfs tree.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
---
 fs/nfs/client.c           | 15 ++++++++++
 fs/nfs/super.c            |  6 +++-
 fs/nfs/sysfs.c            | 58 +++++++++++++++++++++++++++++++++++++++
 fs/nfs/sysfs.h            |  5 ++++
 include/linux/nfs_fs_sb.h |  2 ++
 5 files changed, 85 insertions(+), 1 deletion(-)

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index f50e025ae406..72da715fc617 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -944,6 +944,8 @@ void nfs_server_remove_lists(struct nfs_server *server)
 }
 EXPORT_SYMBOL_GPL(nfs_server_remove_lists);
 
+static DEFINE_IDA(s_sysfs_ids);
+
 /*
  * Allocate and initialise a server record
  */
@@ -955,6 +957,13 @@ struct nfs_server *nfs_alloc_server(void)
 	if (!server)
 		return NULL;
 
+	server->s_sysfs_id = ida_simple_get(
+		&s_sysfs_ids, 0, 0, GFP_KERNEL);
+	if (server->s_sysfs_id < 0) {
+		kfree(server);
+		return NULL;
+	}
+
 	server->client = server->client_acl = ERR_PTR(-EINVAL);
 
 	/* Zero out the NFS state stuff */
@@ -979,6 +988,7 @@ struct nfs_server *nfs_alloc_server(void)
 	ida_init(&server->lockowner_id);
 	pnfs_init_server(server);
 	rpc_init_wait_queue(&server->uoc_rpcwaitq, "NFS UOC");
+	nfs_sysfs_add_server(server);
 
 	return server;
 }
@@ -1001,6 +1011,10 @@ void nfs_free_server(struct nfs_server *server)
 
 	nfs_put_client(server->nfs_client);
 
+	nfs_sysfs_remove_server(server);
+	kobject_put(&server->kobj);
+	ida_simple_remove(&s_sysfs_ids, server->s_sysfs_id);
+
 	ida_destroy(&server->lockowner_id);
 	ida_destroy(&server->openowner_id);
 	nfs_free_iostats(server->io_stats);
@@ -1385,6 +1399,7 @@ int __init nfs_fs_proc_init(void)
 void nfs_fs_proc_exit(void)
 {
 	remove_proc_subtree("fs/nfsfs", NULL);
+	ida_destroy(&s_sysfs_ids);
 }
 
 #endif /* CONFIG_PROC_FS */
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 05ae23657527..40a866db7965 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -68,6 +68,8 @@
 #include "nfs4session.h"
 #include "pnfs.h"
 #include "nfs.h"
+#include "netns.h"
+#include "sysfs.h"
 
 #define NFSDBG_FACILITY		NFSDBG_VFS
 
@@ -1088,6 +1090,7 @@ static void nfs_fill_super(struct super_block *sb, struct nfs_fs_context *ctx)
 						 &sb->s_blocksize_bits);
 
 	nfs_super_set_maxbytes(sb, server->maxfilesize);
+	nfs_sysfs_move_server_to_sb(sb);
 	server->has_sec_mnt_opts = ctx->has_sec_mnt_opts;
 }
 
@@ -1333,13 +1336,14 @@ int nfs_get_tree_common(struct fs_context *fc)
 }
 
 /*
- * Destroy an NFS2/3 superblock
+ * Destroy an NFS superblock
  */
 void nfs_kill_super(struct super_block *s)
 {
 	struct nfs_server *server = NFS_SB(s);
 	dev_t dev = s->s_dev;
 
+	nfs_sysfs_move_sb_to_server(server);
 	generic_shutdown_super(s);
 
 	nfs_fscache_release_super_cookie(s);
diff --git a/fs/nfs/sysfs.c b/fs/nfs/sysfs.c
index a496e26fcfb7..534e2293a698 100644
--- a/fs/nfs/sysfs.c
+++ b/fs/nfs/sysfs.c
@@ -190,3 +190,61 @@ void nfs_netns_sysfs_destroy(struct nfs_net *netns)
 		netns->nfs_client = NULL;
 	}
 }
+
+static void nfs_sysfs_sb_release(struct kobject *kobj)
+{
+	/* no-op: why? see lib/kobject.c kobject_cleanup() */
+}
+
+static struct attribute *nfs_mp_attrs[] = {
+        NULL,
+};
+
+ATTRIBUTE_GROUPS(nfs_mp);
+
+static struct kobj_type nfs_sb_ktype = {
+	.release = nfs_sysfs_sb_release,
+	.sysfs_ops = &kobj_sysfs_ops,
+	.default_groups = nfs_mp_groups,
+};
+
+void nfs_sysfs_add_server(struct nfs_server *server)
+{
+	int ret;
+
+	ret = kobject_init_and_add(&server->kobj, &nfs_sb_ktype,
+				&nfs_kset->kobj, "server-%d", server->s_sysfs_id);
+	if (ret < 0)
+		pr_warn("NFS: nfs sysfs add server-%d failed (%d)\n",
+					server->s_sysfs_id, ret);
+}
+
+void nfs_sysfs_move_server_to_sb(struct super_block *s)
+{
+	struct nfs_server *server = s->s_fs_info;
+	int ret;
+
+	ret = kobject_rename(&server->kobj, s->s_id);
+	if (ret < 0)
+		pr_warn("NFS: rename sysfs %s failed (%d)\n",
+					server->kobj.name, ret);
+}
+
+void nfs_sysfs_move_sb_to_server(struct nfs_server *server)
+{
+	const char *s;
+	int ret = -ENOMEM;
+
+	s = kasprintf(GFP_KERNEL, "server-%d", server->s_sysfs_id);
+	if (s)
+		ret = kobject_rename(&server->kobj, s);
+	if (ret < 0)
+		pr_warn("NFS: rename sysfs %s failed (%d)\n",
+					server->kobj.name, ret);
+}
+
+/* unlink, not dec-ref */
+void nfs_sysfs_remove_server(struct nfs_server *server)
+{
+	kobject_del(&server->kobj);
+}
diff --git a/fs/nfs/sysfs.h b/fs/nfs/sysfs.h
index 0423aaf388c9..0fc80fb55b3e 100644
--- a/fs/nfs/sysfs.h
+++ b/fs/nfs/sysfs.h
@@ -22,4 +22,9 @@ extern void nfs_sysfs_exit(void);
 void nfs_netns_sysfs_setup(struct nfs_net *netns, struct net *net);
 void nfs_netns_sysfs_destroy(struct nfs_net *netns);
 
+void nfs_sysfs_add_server(struct nfs_server *s);
+void nfs_sysfs_move_server_to_sb(struct super_block *s);
+void nfs_sysfs_move_sb_to_server(struct nfs_server *s);
+void nfs_sysfs_remove_server(struct nfs_server *s);
+
 #endif
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index ea2f7e6b1b0b..dee1664abca8 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -183,6 +183,7 @@ struct nfs_server {
 				change_attr_type;/* Description of change attribute */
 
 	struct nfs_fsid		fsid;
+	int			s_sysfs_id;	/* sysfs dentry index */
 	__u64			maxfilesize;	/* maximum file size */
 	struct timespec64	time_delta;	/* smallest time granularity */
 	unsigned long		mount_time;	/* when this fs was mounted */
@@ -259,6 +260,7 @@ struct nfs_server {
 	/* User namespace info */
 	const struct cred	*cred;
 	bool			has_sec_mnt_opts;
+	struct kobject	kobj;
 };
 
 /* Server capabilities */
-- 
2.39.2