SUNRPC: take a xprt offline using sysfs

Using sysfs's xprt_state attribute, mark a particular transport offline.
It will not be picked during the round-robin selection. It's not allowed
to take the main (1st created transport associated with the rpc_client)
offline. Also bring a transport back online via sysfs by writing "online"
and that would allow for this transport to be picked during the round-
robin selection.
Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

include/linux/sunrpc/xprt.h

@@ -427,6 +427,7 @@ void			xprt_release_write(struct rpc_xprt *, struct rpc_task *);
 #define XPRT_BOUND		(4)
 #define XPRT_BINDING		(5)
 #define XPRT_CLOSING		(6)
+#define XPRT_OFFLINE		(7)
 #define XPRT_CONGESTED		(9)
 #define XPRT_CWND_WAIT		(10)
 #define XPRT_WRITE_SPACE	(11)

net/sunrpc/sysfs.c

@@ -68,6 +68,15 @@ rpc_sysfs_xprt_kobj_get_xprt(struct kobject *kobj)
 	return xprt_get(x->xprt);
 }
 
+static inline struct rpc_xprt_switch *
+rpc_sysfs_xprt_kobj_get_xprt_switch(struct kobject *kobj)
+{
+	struct rpc_sysfs_xprt *x = container_of(kobj,
+		struct rpc_sysfs_xprt, kobject);
+
+	return xprt_switch_get(x->xprt_switch);
+}
+
 static inline struct rpc_xprt_switch *
 rpc_sysfs_xprt_switch_kobj_get_xprt(struct kobject *kobj)
 {
@@ -122,7 +131,7 @@ static ssize_t rpc_sysfs_xprt_state_show(struct kobject *kobj,
 	struct rpc_xprt *xprt = rpc_sysfs_xprt_kobj_get_xprt(kobj);
 	ssize_t ret;
 	int locked, connected, connecting, close_wait, bound, binding,
-	    closing, congested, cwnd_wait, write_space;
+	    closing, congested, cwnd_wait, write_space, offline;
 
 	if (!xprt)
 		return 0;
@@ -140,8 +149,9 @@ static ssize_t rpc_sysfs_xprt_state_show(struct kobject *kobj,
 		congested = test_bit(XPRT_CONGESTED, &xprt->state);
 		cwnd_wait = test_bit(XPRT_CWND_WAIT, &xprt->state);
 		write_space = test_bit(XPRT_WRITE_SPACE, &xprt->state);
+		offline = test_bit(XPRT_OFFLINE, &xprt->state);
 
-		ret = sprintf(buf, "state=%s %s %s %s %s %s %s %s %s %s\n",
+		ret = sprintf(buf, "state=%s %s %s %s %s %s %s %s %s %s %s\n",
 			      locked ? "LOCKED" : "",
 			      connected ? "CONNECTED" : "",
 			      connecting ? "CONNECTING" : "",
@@ -151,7 +161,8 @@ static ssize_t rpc_sysfs_xprt_state_show(struct kobject *kobj,
 			      closing ? "CLOSING" : "",
 			      congested ? "CONGESTED" : "",
 			      cwnd_wait ? "CWND_WAIT" : "",
-			      write_space ? "WRITE_SPACE" : "");
+			      write_space ? "WRITE_SPACE" : "",
+			      offline ? "OFFLINE" : "");
 	}
 
 	xprt_put(xprt);
@@ -233,6 +244,52 @@ static ssize_t rpc_sysfs_xprt_dstaddr_store(struct kobject *kobj,
 	goto out;
 }
 
+static ssize_t rpc_sysfs_xprt_state_change(struct kobject *kobj,
+					   struct kobj_attribute *attr,
+					   const char *buf, size_t count)
+{
+	struct rpc_xprt *xprt = rpc_sysfs_xprt_kobj_get_xprt(kobj);
+	int offline = 0, online = 0;
+	struct rpc_xprt_switch *xps = rpc_sysfs_xprt_kobj_get_xprt_switch(kobj);
+
+	if (!xprt)
+		return 0;
+
+	if (!strncmp(buf, "offline", 7))
+		offline = 1;
+	else if (!strncmp(buf, "online", 6))
+		online = 1;
+	else
+		return -EINVAL;
+
+	if (wait_on_bit_lock(&xprt->state, XPRT_LOCKED, TASK_KILLABLE)) {
+		count = -EINTR;
+		goto out_put;
+	}
+	if (xprt->main) {
+		count = -EINVAL;
+		goto release_tasks;
+	}
+	if (offline) {
+		set_bit(XPRT_OFFLINE, &xprt->state);
+		spin_lock(&xps->xps_lock);
+		xps->xps_nactive--;
+		spin_unlock(&xps->xps_lock);
+	} else if (online) {
+		clear_bit(XPRT_OFFLINE, &xprt->state);
+		spin_lock(&xps->xps_lock);
+		xps->xps_nactive++;
+		spin_unlock(&xps->xps_lock);
+	}
+
+release_tasks:
+	xprt_release_write(xprt, NULL);
+out_put:
+	xprt_put(xprt);
+	xprt_switch_put(xps);
+	return count;
+}
+
 int rpc_sysfs_init(void)
 {
 	rpc_sunrpc_kset = kset_create_and_add("sunrpc", NULL, kernel_kobj);
@@ -303,7 +360,7 @@ static struct kobj_attribute rpc_sysfs_xprt_info = __ATTR(xprt_info,
 	0444, rpc_sysfs_xprt_info_show, NULL);
 
 static struct kobj_attribute rpc_sysfs_xprt_change_state = __ATTR(xprt_state,
-	0644, rpc_sysfs_xprt_state_show, NULL);
+	0644, rpc_sysfs_xprt_state_show, rpc_sysfs_xprt_state_change);
 
 static struct attribute *rpc_sysfs_xprt_attrs[] = {
 	&rpc_sysfs_xprt_dstaddr.attr,
@@ -466,6 +523,7 @@ void rpc_sysfs_xprt_setup(struct rpc_xprt_switch *xprt_switch,
 	if (rpc_xprt) {
 		xprt->xprt_sysfs = rpc_xprt;
 		rpc_xprt->xprt = xprt;
+		rpc_xprt->xprt_switch = xprt_switch;
 		kobject_uevent(&rpc_xprt->kobject, KOBJ_ADD);
 	}
 }

net/sunrpc/sysfs.h

@@ -22,6 +22,7 @@ struct rpc_sysfs_xprt_switch {
 struct rpc_sysfs_xprt {
 	struct kobject kobject;
 	struct rpc_xprt *xprt;
+	struct rpc_xprt_switch *xprt_switch;
 };
 
 int rpc_sysfs_init(void);

net/sunrpc/xprtmultipath.c

@@ -65,6 +65,7 @@ static void xprt_switch_remove_xprt_locked(struct rpc_xprt_switch *xps,
 {
 	if (unlikely(xprt == NULL))
 		return;
+	if (!test_bit(XPRT_OFFLINE, &xprt->state))
 		xps->xps_nactive--;
 	xps->xps_nxprts--;
 	if (xps->xps_nxprts == 0)
@@ -230,7 +231,8 @@ void xprt_iter_default_rewind(struct rpc_xprt_iter *xpi)
 static
 bool xprt_is_active(const struct rpc_xprt *xprt)
 {
-	return kref_read(&xprt->kref) != 0;
+	return (kref_read(&xprt->kref) != 0 &&
+		!test_bit(XPRT_OFFLINE, &xprt->state));
 }
 
 static