/* 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 <linux/fs.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/sched/signal.h>
#include "internal.h"
#include "afs_fs.h"

/*
 * Initialise a filesystem server cursor for iterating over FS servers.
 */
static void afs_init_fs_cursor(struct afs_fs_cursor *fc, struct afs_vnode *vnode)
{
        memset(fc, 0, sizeof(*fc));
}

/*
 * Begin an operation on the fileserver.
 *
 * Fileserver operations are serialised on the server by vnode, so we serialise
 * them here also using the io_lock.
 */
bool afs_begin_vnode_operation(struct afs_fs_cursor *fc, struct afs_vnode *vnode,
                               struct key *key)
{
        afs_init_fs_cursor(fc, vnode);
        fc->vnode = vnode;
        fc->key = key;
        fc->ac.error = SHRT_MAX;

        if (mutex_lock_interruptible(&vnode->io_lock) < 0) {
                fc->ac.error = -EINTR;
                fc->flags |= AFS_FS_CURSOR_STOP;
                return false;
        }

        if (vnode->lock_state != AFS_VNODE_LOCK_NONE)
                fc->flags |= AFS_FS_CURSOR_CUR_ONLY;
        return true;
}

/*
 * Begin iteration through a server list, starting with the vnode's last used
 * server if possible, or the last recorded good server if not.
 */
static bool afs_start_fs_iteration(struct afs_fs_cursor *fc,
                                   struct afs_vnode *vnode)
{
        struct afs_cb_interest *cbi;
        int i;

        read_lock(&vnode->volume->servers_lock);
        fc->server_list = afs_get_serverlist(vnode->volume->servers);
        read_unlock(&vnode->volume->servers_lock);

        cbi = vnode->cb_interest;
        if (cbi) {
                /* See if the vnode's preferred record is still available */
                for (i = 0; i < fc->server_list->nr_servers; i++) {
                        if (fc->server_list->servers[i].cb_interest == cbi) {
                                fc->start = i;
                                goto found_interest;
                        }
                }

                /* If we have a lock outstanding on a server that's no longer
                 * serving this vnode, then we can't switch to another server
                 * and have to return an error.
                 */
                if (fc->flags & AFS_FS_CURSOR_CUR_ONLY) {
                        fc->ac.error = -ESTALE;
                        return false;
                }

                /* Note that the callback promise is effectively broken */
                write_seqlock(&vnode->cb_lock);
                ASSERTCMP(cbi, ==, vnode->cb_interest);
                vnode->cb_interest = NULL;
                if (test_and_clear_bit(AFS_VNODE_CB_PROMISED, &vnode->flags))
                        vnode->cb_break++;
                write_sequnlock(&vnode->cb_lock);

                afs_put_cb_interest(afs_v2net(vnode), cbi);
                cbi = NULL;
        } else {
                fc->start = READ_ONCE(fc->server_list->index);
        }

found_interest:
        fc->index = fc->start;
        return true;
}

/*
 * Post volume busy note.
 */
static void afs_busy(struct afs_volume *volume, u32 abort_code)
{
        const char *m;

        switch (abort_code) {
        case VOFFLINE:          m = "offline";          break;
        case VRESTARTING:       m = "restarting";       break;
        case VSALVAGING:        m = "being salvaged";   break;
        default:                m = "busy";             break;
        }

        pr_notice("kAFS: Volume %u '%s' is %s\n", volume->vid, volume->name, m);
}

/*
 * Sleep and retry the operation to the same fileserver.
 */
static bool afs_sleep_and_retry(struct afs_fs_cursor *fc)
{
        msleep_interruptible(1000);
        if (signal_pending(current)) {
                fc->ac.error = -ERESTARTSYS;
                return false;
        }

        return true;
}

/*
 * Select the fileserver to use.  May be called multiple times to rotate
 * through the fileservers.
 */
bool afs_select_fileserver(struct afs_fs_cursor *fc)
{
        struct afs_addr_list *alist;
        struct afs_server *server;
        struct afs_vnode *vnode = fc->vnode;

        _enter("%u/%u,%u/%u,%d,%d",
               fc->index, fc->start,
               fc->ac.index, fc->ac.start,
               fc->ac.error, fc->ac.abort_code);

        if (fc->flags & AFS_FS_CURSOR_STOP) {
                _leave(" = f [stopped]");
                return false;
        }

        /* Evaluate the result of the previous operation, if there was one. */
        switch (fc->ac.error) {
        case SHRT_MAX:
                goto start;

        case 0:
        default:
                /* Success or local failure.  Stop. */
                fc->flags |= AFS_FS_CURSOR_STOP;
                _leave(" = f [okay/local %d]", fc->ac.error);
                return false;

        case -ECONNABORTED:
                /* The far side rejected the operation on some grounds.  This
                 * might involve the server being busy or the volume having been moved.
                 */
                switch (fc->ac.abort_code) {
                case VNOVOL:
                        /* This fileserver doesn't know about the volume.
                         * - May indicate that the VL is wrong - retry once and compare
                         *   the results.
                         * - May indicate that the fileserver couldn't attach to the vol.
                         */
                        if (fc->flags & AFS_FS_CURSOR_VNOVOL) {
                                fc->ac.error = -EREMOTEIO;
                                goto next_server;
                        }

                        write_lock(&vnode->volume->servers_lock);
                        fc->server_list->vnovol_mask |= 1 << fc->index;
                        write_unlock(&vnode->volume->servers_lock);

                        set_bit(AFS_VOLUME_NEEDS_UPDATE, &vnode->volume->flags);
                        fc->ac.error = afs_check_volume_status(vnode->volume, fc->key);
                        if (fc->ac.error < 0)
                                goto failed;

                        if (test_bit(AFS_VOLUME_DELETED, &vnode->volume->flags)) {
                                fc->ac.error = -ENOMEDIUM;
                                goto failed;
                        }

                        /* If the server list didn't change, then assume that
                         * it's the fileserver having trouble.
                         */
                        if (vnode->volume->servers == fc->server_list) {
                                fc->ac.error = -EREMOTEIO;
                                goto next_server;
                        }

                        /* Try again */
                        fc->flags |= AFS_FS_CURSOR_VNOVOL;
                        _leave(" = t [vnovol]");
                        return true;

                case VSALVAGE: /* TODO: Should this return an error or iterate? */
                case VVOLEXISTS:
                case VNOSERVICE:
                case VONLINE:
                case VDISKFULL:
                case VOVERQUOTA:
                        fc->ac.error = afs_abort_to_error(fc->ac.abort_code);
                        goto next_server;

                case VOFFLINE:
                        if (!test_and_set_bit(AFS_VOLUME_OFFLINE, &vnode->volume->flags)) {
                                afs_busy(vnode->volume, fc->ac.abort_code);
                                clear_bit(AFS_VOLUME_BUSY, &vnode->volume->flags);
                        }
                        if (fc->flags & AFS_FS_CURSOR_NO_VSLEEP) {
                                fc->ac.error = -EADV;
                                goto failed;
                        }
                        if (fc->flags & AFS_FS_CURSOR_CUR_ONLY) {
                                fc->ac.error = -ESTALE;
                                goto failed;
                        }
                        goto busy;

                case VSALVAGING:
                case VRESTARTING:
                case VBUSY:
                        /* Retry after going round all the servers unless we
                         * have a file lock we need to maintain.
                         */
                        if (fc->flags & AFS_FS_CURSOR_NO_VSLEEP) {
                                fc->ac.error = -EBUSY;
                                goto failed;
                        }
                        if (!test_and_set_bit(AFS_VOLUME_BUSY, &vnode->volume->flags)) {
                                afs_busy(vnode->volume, fc->ac.abort_code);
                                clear_bit(AFS_VOLUME_OFFLINE, &vnode->volume->flags);
                        }
                busy:
                        if (fc->flags & AFS_FS_CURSOR_CUR_ONLY) {
                                if (!afs_sleep_and_retry(fc))
                                        goto failed;

                                 /* Retry with same server & address */
                                _leave(" = t [vbusy]");
                                return true;
                        }

                        fc->flags |= AFS_FS_CURSOR_VBUSY;
                        goto next_server;

                case VMOVED:
                        /* The volume migrated to another server.  We consider
                         * consider all locks and callbacks broken and request
                         * an update from the VLDB.
                         *
                         * We also limit the number of VMOVED hops we will
                         * honour, just in case someone sets up a loop.
                         */
                        if (fc->flags & AFS_FS_CURSOR_VMOVED) {
                                fc->ac.error = -EREMOTEIO;
                                goto failed;
                        }
                        fc->flags |= AFS_FS_CURSOR_VMOVED;

                        set_bit(AFS_VOLUME_WAIT, &vnode->volume->flags);
                        set_bit(AFS_VOLUME_NEEDS_UPDATE, &vnode->volume->flags);
                        fc->ac.error = afs_check_volume_status(vnode->volume, fc->key);
                        if (fc->ac.error < 0)
                                goto failed;

                        /* If the server list didn't change, then the VLDB is
                         * out of sync with the fileservers.  This is hopefully
                         * a temporary condition, however, so we don't want to
                         * permanently block access to the file.
                         *
                         * TODO: Try other fileservers if we can.
                         *
                         * TODO: Retry a few times with sleeps.
                         */
                        if (vnode->volume->servers == fc->server_list) {
                                fc->ac.error = -ENOMEDIUM;
                                goto failed;
                        }

                        goto restart_from_beginning;

                default:
                        clear_bit(AFS_VOLUME_OFFLINE, &vnode->volume->flags);
                        clear_bit(AFS_VOLUME_BUSY, &vnode->volume->flags);
                        fc->ac.error = afs_abort_to_error(fc->ac.abort_code);
                        goto failed;
                }

        case -ENETUNREACH:
        case -EHOSTUNREACH:
        case -ECONNREFUSED:
        case -ETIMEDOUT:
        case -ETIME:
                _debug("no conn");
                goto iterate_address;

        case -ECONNRESET:
                _debug("call reset");
                goto failed;
        }

restart_from_beginning:
        _debug("restart");
        afs_end_cursor(&fc->ac);
        afs_put_cb_interest(afs_v2net(vnode), fc->cbi);
        fc->cbi = NULL;
        afs_put_serverlist(afs_v2net(vnode), fc->server_list);
        fc->server_list = NULL;
start:
        _debug("start");
        /* See if we need to do an update of the volume record.  Note that the
         * volume may have moved or even have been deleted.
         */
        fc->ac.error = afs_check_volume_status(vnode->volume, fc->key);
        if (fc->ac.error < 0)
                goto failed;

        if (!afs_start_fs_iteration(fc, vnode))
                goto failed;

use_server:
        _debug("use");
        /* We're starting on a different fileserver from the list.  We need to
         * check it, create a callback intercept, find its address list and
         * probe its capabilities before we use it.
         */
        ASSERTCMP(fc->ac.alist, ==, NULL);
        server = fc->server_list->servers[fc->index].server;

        if (!afs_check_server_record(fc, server))
                goto failed;

        _debug("USING SERVER: %pU", &server->uuid);

        /* Make sure we've got a callback interest record for this server.  We
         * have to link it in before we send the request as we can be sent a
         * break request before we've finished decoding the reply and
         * installing the vnode.
         */
        fc->ac.error = afs_register_server_cb_interest(vnode, fc->server_list,
                                                       fc->index);
        if (fc->ac.error < 0)
                goto failed;

        fc->cbi = afs_get_cb_interest(vnode->cb_interest);

        read_lock(&server->fs_lock);
        alist = rcu_dereference_protected(server->addresses,
                                          lockdep_is_held(&server->fs_lock));
        afs_get_addrlist(alist);
        read_unlock(&server->fs_lock);

        memset(&fc->ac, 0, sizeof(fc->ac));

        /* Probe the current fileserver if we haven't done so yet. */
        if (!test_bit(AFS_SERVER_FL_PROBED, &server->flags)) {
                fc->ac.alist = afs_get_addrlist(alist);

                if (!afs_probe_fileserver(fc)) {
                        switch (fc->ac.error) {
                        case -ENOMEM:
                        case -ERESTARTSYS:
                        case -EINTR:
                                goto failed;
                        default:
                                goto next_server;
                        }
                }
        }

        if (!fc->ac.alist)
                fc->ac.alist = alist;
        else
                afs_put_addrlist(alist);

        fc->ac.start = READ_ONCE(alist->index);
        fc->ac.index = fc->ac.start;

iterate_address:
        ASSERT(fc->ac.alist);
        _debug("iterate %d/%d", fc->ac.index, fc->ac.alist->nr_addrs);
        /* Iterate over the current server's address list to try and find an
         * address on which it will respond to us.
         */
        if (!afs_iterate_addresses(&fc->ac))
                goto next_server;

        _leave(" = t");
        return true;

next_server:
        _debug("next");
        afs_end_cursor(&fc->ac);
        afs_put_cb_interest(afs_v2net(vnode), fc->cbi);
        fc->cbi = NULL;
        fc->index++;
        if (fc->index >= fc->server_list->nr_servers)
                fc->index = 0;
        if (fc->index != fc->start)
                goto use_server;

        /* That's all the servers poked to no good effect.  Try again if some
         * of them were busy.
         */
        if (fc->flags & AFS_FS_CURSOR_VBUSY)
                goto restart_from_beginning;

        fc->ac.error = -EDESTADDRREQ;
        goto failed;

failed:
        fc->flags |= AFS_FS_CURSOR_STOP;
        afs_end_cursor(&fc->ac);
        _leave(" = f [failed %d]", fc->ac.error);
        return false;
}

/*
 * Select the same fileserver we used for a vnode before and only that
 * fileserver.  We use this when we have a lock on that file, which is backed
 * only by the fileserver we obtained it from.
 */
bool afs_select_current_fileserver(struct afs_fs_cursor *fc)
{
        struct afs_vnode *vnode = fc->vnode;
        struct afs_cb_interest *cbi = vnode->cb_interest;
        struct afs_addr_list *alist;

        _enter("");

        switch (fc->ac.error) {
        case SHRT_MAX:
                if (!cbi) {
                        fc->ac.error = -ESTALE;
                        fc->flags |= AFS_FS_CURSOR_STOP;
                        return false;
                }

                fc->cbi = afs_get_cb_interest(vnode->cb_interest);

                read_lock(&cbi->server->fs_lock);
                alist = rcu_dereference_protected(cbi->server->addresses,
                                                  lockdep_is_held(&cbi->server->fs_lock));
                afs_get_addrlist(alist);
                read_unlock(&cbi->server->fs_lock);
                if (!alist) {
                        fc->ac.error = -ESTALE;
                        fc->flags |= AFS_FS_CURSOR_STOP;
                        return false;
                }

                memset(&fc->ac, 0, sizeof(fc->ac));
                fc->ac.alist = alist;
                fc->ac.start = READ_ONCE(alist->index);
                fc->ac.index = fc->ac.start;
                goto iterate_address;

        case 0:
        default:
                /* Success or local failure.  Stop. */
                fc->flags |= AFS_FS_CURSOR_STOP;
                _leave(" = f [okay/local %d]", fc->ac.error);
                return false;

        case -ECONNABORTED:
                fc->flags |= AFS_FS_CURSOR_STOP;
                _leave(" = f [abort]");
                return false;

        case -ENETUNREACH:
        case -EHOSTUNREACH:
        case -ECONNREFUSED:
        case -ETIMEDOUT:
        case -ETIME:
                _debug("no conn");
                goto iterate_address;
        }

iterate_address:
        /* Iterate over the current server's address list to try and find an
         * address on which it will respond to us.
         */
        if (afs_iterate_addresses(&fc->ac)) {
                _leave(" = t");
                return true;
        }

        afs_end_cursor(&fc->ac);
        return false;
}

/*
 * Tidy up a filesystem cursor and unlock the vnode.
 */
int afs_end_vnode_operation(struct afs_fs_cursor *fc)
{
        struct afs_net *net = afs_v2net(fc->vnode);
        int ret;

        mutex_unlock(&fc->vnode->io_lock);

        afs_end_cursor(&fc->ac);
        afs_put_cb_interest(net, fc->cbi);
        afs_put_serverlist(net, fc->server_list);

        ret = fc->ac.error;
        if (ret == -ECONNABORTED)
                afs_abort_to_error(fc->ac.abort_code);

        return fc->ac.error;
}