/* 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;
}