afs: Move server rotation code into its own file

Move server rotation code into its own file.

Signed-off-by: David Howells <dhowells@redhat.com>

fs/afs/Makefile

@@ -20,6 +20,7 @@ kafs-objs := \
 	misc.o \
 	mntpt.o \
 	proc.o \
+	rotate.o \
 	rxrpc.o \
 	security.o \
 	server.o \

fs/afs/rotate.c

@@ -0,0 +1,254 @@
+/* Handle fileserver selection and rotation.
+ *
+ * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include "internal.h"
+
+/*
+ * Initialise a filesystem server cursor for iterating over FS servers.
+ */
+void afs_init_fs_cursor(struct afs_fs_cursor *fc, struct afs_vnode *vnode)
+{
+	memset(fc, 0, sizeof(*fc));
+}
+
+/*
+ * Set a filesystem server cursor for using a specific FS server.
+ */
+int afs_set_fs_cursor(struct afs_fs_cursor *fc, struct afs_vnode *vnode)
+{
+	afs_init_fs_cursor(fc, vnode);
+
+	read_seqlock_excl(&vnode->cb_lock);
+	if (vnode->cb_interest) {
+		if (vnode->cb_interest->server->fs_state == 0)
+			fc->server = afs_get_server(vnode->cb_interest->server);
+		else
+			fc->ac.error = vnode->cb_interest->server->fs_state;
+	} else {
+		fc->ac.error = -ESTALE;
+	}
+	read_sequnlock_excl(&vnode->cb_lock);
+
+	return fc->ac.error;
+}
+
+/*
+ * pick a server to use to try accessing this volume
+ * - returns with an elevated usage count on the server chosen
+ */
+bool afs_volume_pick_fileserver(struct afs_fs_cursor *fc, struct afs_vnode *vnode)
+{
+	struct afs_volume *volume = vnode->volume;
+	struct afs_server *server;
+	int ret, state, loop;
+
+	_enter("%s", volume->vlocation->vldb.name);
+
+	/* stick with the server we're already using if we can */
+	if (vnode->cb_interest && vnode->cb_interest->server->fs_state == 0) {
+		fc->server = afs_get_server(vnode->cb_interest->server);
+		goto set_server;
+	}
+
+	down_read(&volume->server_sem);
+
+	/* handle the no-server case */
+	if (volume->nservers == 0) {
+		fc->ac.error = volume->rjservers ? -ENOMEDIUM : -ESTALE;
+		up_read(&volume->server_sem);
+		_leave(" = f [no servers %d]", fc->ac.error);
+		return false;
+	}
+
+	/* basically, just search the list for the first live server and use
+	 * that */
+	ret = 0;
+	for (loop = 0; loop < volume->nservers; loop++) {
+		server = volume->servers[loop];
+		state = server->fs_state;
+
+		_debug("consider %d [%d]", loop, state);
+
+		switch (state) {
+		case 0:
+			goto picked_server;
+
+		case -ENETUNREACH:
+			if (ret == 0)
+				ret = state;
+			break;
+
+		case -EHOSTUNREACH:
+			if (ret == 0 ||
+			    ret == -ENETUNREACH)
+				ret = state;
+			break;
+
+		case -ECONNREFUSED:
+			if (ret == 0 ||
+			    ret == -ENETUNREACH ||
+			    ret == -EHOSTUNREACH)
+				ret = state;
+			break;
+
+		default:
+		case -EREMOTEIO:
+			if (ret == 0 ||
+			    ret == -ENETUNREACH ||
+			    ret == -EHOSTUNREACH ||
+			    ret == -ECONNREFUSED)
+				ret = state;
+			break;
+		}
+	}
+
+error:
+	fc->ac.error = ret;
+
+	/* no available servers
+	 * - TODO: handle the no active servers case better
+	 */
+	up_read(&volume->server_sem);
+	_leave(" = f [%d]", fc->ac.error);
+	return false;
+
+picked_server:
+	/* Found an apparently healthy server.  We need to register an interest
+	 * in receiving callbacks before we talk to it.
+	 */
+	ret = afs_register_server_cb_interest(vnode,
+					      &volume->cb_interests[loop], server);
+	if (ret < 0)
+		goto error;
+
+	fc->server = afs_get_server(server);
+	up_read(&volume->server_sem);
+set_server:
+	fc->ac.alist = afs_get_addrlist(fc->server->addrs);
+	fc->ac.addr = &fc->ac.alist->addrs[0];
+	_debug("USING SERVER: %pIS\n", &fc->ac.addr->transport);
+	_leave(" = t (picked %pIS)", &fc->ac.addr->transport);
+	return true;
+}
+
+/*
+ * release a server after use
+ * - releases the ref on the server struct that was acquired by picking
+ * - records result of using a particular server to access a volume
+ * - return true to try again, false if okay or to issue error
+ * - the caller must release the server struct if result was false
+ */
+bool afs_iterate_fs_cursor(struct afs_fs_cursor *fc,
+			   struct afs_vnode *vnode)
+{
+	struct afs_volume *volume = vnode->volume;
+	struct afs_server *server = fc->server;
+	unsigned loop;
+
+	_enter("%s,%pIS,%d",
+	       volume->vlocation->vldb.name, &fc->ac.addr->transport,
+	       fc->ac.error);
+
+	switch (fc->ac.error) {
+		/* success */
+	case 0:
+		server->fs_state = 0;
+		_leave(" = f");
+		return false;
+
+		/* the fileserver denied all knowledge of the volume */
+	case -ENOMEDIUM:
+		down_write(&volume->server_sem);
+
+		/* firstly, find where the server is in the active list (if it
+		 * is) */
+		for (loop = 0; loop < volume->nservers; loop++)
+			if (volume->servers[loop] == server)
+				goto present;
+
+		/* no longer there - may have been discarded by another op */
+		goto try_next_server_upw;
+
+	present:
+		volume->nservers--;
+		memmove(&volume->servers[loop],
+			&volume->servers[loop + 1],
+			sizeof(volume->servers[loop]) *
+			(volume->nservers - loop));
+		volume->servers[volume->nservers] = NULL;
+		afs_put_server(afs_v2net(vnode), server);
+		volume->rjservers++;
+
+		if (volume->nservers > 0)
+			/* another server might acknowledge its existence */
+			goto try_next_server_upw;
+
+		/* handle the case where all the fileservers have rejected the
+		 * volume
+		 * - TODO: try asking the fileservers for volume information
+		 * - TODO: contact the VL server again to see if the volume is
+		 *         no longer registered
+		 */
+		up_write(&volume->server_sem);
+		afs_put_server(afs_v2net(vnode), server);
+		fc->server = NULL;
+		_leave(" = f [completely rejected]");
+		return false;
+
+		/* problem reaching the server */
+	case -ENETUNREACH:
+	case -EHOSTUNREACH:
+	case -ECONNREFUSED:
+	case -ETIME:
+	case -ETIMEDOUT:
+	case -EREMOTEIO:
+		/* mark the server as dead
+		 * TODO: vary dead timeout depending on error
+		 */
+		spin_lock(&server->fs_lock);
+		if (!server->fs_state) {
+			server->fs_state = fc->ac.error;
+			printk("kAFS: SERVER DEAD state=%d\n", fc->ac.error);
+		}
+		spin_unlock(&server->fs_lock);
+		goto try_next_server;
+
+		/* miscellaneous error */
+	default:
+	case -ENOMEM:
+	case -ENONET:
+		/* tell the caller to accept the result */
+		afs_put_server(afs_v2net(vnode), server);
+		fc->server = NULL;
+		_leave(" = f [local failure]");
+		return false;
+	}
+
+	/* tell the caller to loop around and try the next server */
+try_next_server_upw:
+	up_write(&volume->server_sem);
+try_next_server:
+	afs_put_server(afs_v2net(vnode), server);
+	_leave(" = t [try next server]");
+	return true;
+}
+
+/*
+ * Clean up a fileserver cursor.
+ */
+int afs_end_fs_cursor(struct afs_fs_cursor *fc, struct afs_net *net)
+{
+	afs_end_cursor(&fc->ac);
+	afs_put_server(net, fc->server);
+	return fc->ac.error;
+}