/* AFS file locking support
 *
 * Copyright (C) 2007 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 License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include "internal.h"

#define AFS_LOCK_GRANTED        0
#define AFS_LOCK_PENDING        1

static void afs_fl_copy_lock(struct file_lock *new, struct file_lock *fl);
static void afs_fl_release_private(struct file_lock *fl);

static struct workqueue_struct *afs_lock_manager;
static DEFINE_MUTEX(afs_lock_manager_mutex);

static const struct file_lock_operations afs_lock_ops = {
        .fl_copy_lock           = afs_fl_copy_lock,
        .fl_release_private     = afs_fl_release_private,
};

/*
 * initialise the lock manager thread if it isn't already running
 */
static int afs_init_lock_manager(void)
{
        int ret;

        ret = 0;
        if (!afs_lock_manager) {
                mutex_lock(&afs_lock_manager_mutex);
                if (!afs_lock_manager) {
                        afs_lock_manager =
                                create_singlethread_workqueue("kafs_lockd");
                        if (!afs_lock_manager)
                                ret = -ENOMEM;
                }
                mutex_unlock(&afs_lock_manager_mutex);
        }
        return ret;
}

/*
 * destroy the lock manager thread if it's running
 */
void __exit afs_kill_lock_manager(void)
{
        if (afs_lock_manager)
                destroy_workqueue(afs_lock_manager);
}

/*
 * if the callback is broken on this vnode, then the lock may now be available
 */
void afs_lock_may_be_available(struct afs_vnode *vnode)
{
        _enter("{%x:%u}", vnode->fid.vid, vnode->fid.vnode);

        queue_delayed_work(afs_lock_manager, &vnode->lock_work, 0);
}

/*
 * the lock will time out in 5 minutes unless we extend it, so schedule
 * extension in a bit less than that time
 */
static void afs_schedule_lock_extension(struct afs_vnode *vnode)
{
        queue_delayed_work(afs_lock_manager, &vnode->lock_work,
                           AFS_LOCKWAIT * HZ / 2);
}

/*
 * grant one or more locks (readlocks are allowed to jump the queue if the
 * first lock in the queue is itself a readlock)
 * - the caller must hold the vnode lock
 */
static void afs_grant_locks(struct afs_vnode *vnode, struct file_lock *fl)
{
        struct file_lock *p, *_p;

        list_move_tail(&fl->fl_u.afs.link, &vnode->granted_locks);
        if (fl->fl_type == F_RDLCK) {
                list_for_each_entry_safe(p, _p, &vnode->pending_locks,
                                         fl_u.afs.link) {
                        if (p->fl_type == F_RDLCK) {
                                p->fl_u.afs.state = AFS_LOCK_GRANTED;
                                list_move_tail(&p->fl_u.afs.link,
                                               &vnode->granted_locks);
                                wake_up(&p->fl_wait);
                        }
                }
        }
}

/*
 * do work for a lock, including:
 * - probing for a lock we're waiting on but didn't get immediately
 * - extending a lock that's close to timing out
 */
void afs_lock_work(struct work_struct *work)
{
        struct afs_vnode *vnode =
                container_of(work, struct afs_vnode, lock_work.work);
        struct file_lock *fl;
        afs_lock_type_t type;
        struct key *key;
        int ret;

        _enter("{%x:%u}", vnode->fid.vid, vnode->fid.vnode);

        spin_lock(&vnode->lock);

        if (test_bit(AFS_VNODE_UNLOCKING, &vnode->flags)) {
                _debug("unlock");
                spin_unlock(&vnode->lock);

                /* attempt to release the server lock; if it fails, we just
                 * wait 5 minutes and it'll time out anyway */
                ret = afs_vnode_release_lock(vnode, vnode->unlock_key);
                if (ret < 0)
                        printk(KERN_WARNING "AFS:"
                               " Failed to release lock on {%x:%x} error %d\n",
                               vnode->fid.vid, vnode->fid.vnode, ret);

                spin_lock(&vnode->lock);
                key_put(vnode->unlock_key);
                vnode->unlock_key = NULL;
                clear_bit(AFS_VNODE_UNLOCKING, &vnode->flags);
        }

        /* if we've got a lock, then it must be time to extend that lock as AFS
         * locks time out after 5 minutes */
        if (!list_empty(&vnode->granted_locks)) {
                _debug("extend");

                if (test_and_set_bit(AFS_VNODE_LOCKING, &vnode->flags))
                        BUG();
                fl = list_entry(vnode->granted_locks.next,
                                struct file_lock, fl_u.afs.link);
                key = key_get(fl->fl_file->private_data);
                spin_unlock(&vnode->lock);

                ret = afs_vnode_extend_lock(vnode, key);
                clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
                key_put(key);
                switch (ret) {
                case 0:
                        afs_schedule_lock_extension(vnode);
                        break;
                default:
                        /* ummm... we failed to extend the lock - retry
                         * extension shortly */
                        printk(KERN_WARNING "AFS:"
                               " Failed to extend lock on {%x:%x} error %d\n",
                               vnode->fid.vid, vnode->fid.vnode, ret);
                        queue_delayed_work(afs_lock_manager, &vnode->lock_work,
                                           HZ * 10);
                        break;
                }
                _leave(" [extend]");
                return;
        }

        /* if we don't have a granted lock, then we must've been called back by
         * the server, and so if might be possible to get a lock we're
         * currently waiting for */
        if (!list_empty(&vnode->pending_locks)) {
                _debug("get");

                if (test_and_set_bit(AFS_VNODE_LOCKING, &vnode->flags))
                        BUG();
                fl = list_entry(vnode->pending_locks.next,
                                struct file_lock, fl_u.afs.link);
                key = key_get(fl->fl_file->private_data);
                type = (fl->fl_type == F_RDLCK) ?
                        AFS_LOCK_READ : AFS_LOCK_WRITE;
                spin_unlock(&vnode->lock);

                ret = afs_vnode_set_lock(vnode, key, type);
                clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
                switch (ret) {
                case -EWOULDBLOCK:
                        _debug("blocked");
                        break;
                case 0:
                        _debug("acquired");
                        if (type == AFS_LOCK_READ)
                                set_bit(AFS_VNODE_READLOCKED, &vnode->flags);
                        else
                                set_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
                        ret = AFS_LOCK_GRANTED;
                default:
                        spin_lock(&vnode->lock);
                        /* the pending lock may have been withdrawn due to a
                         * signal */
                        if (list_entry(vnode->pending_locks.next,
                                       struct file_lock, fl_u.afs.link) == fl) {
                                fl->fl_u.afs.state = ret;
                                if (ret == AFS_LOCK_GRANTED)
                                        afs_grant_locks(vnode, fl);
                                else
                                        list_del_init(&fl->fl_u.afs.link);
                                wake_up(&fl->fl_wait);
                                spin_unlock(&vnode->lock);
                        } else {
                                _debug("withdrawn");
                                clear_bit(AFS_VNODE_READLOCKED, &vnode->flags);
                                clear_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
                                spin_unlock(&vnode->lock);
                                afs_vnode_release_lock(vnode, key);
                                if (!list_empty(&vnode->pending_locks))
                                        afs_lock_may_be_available(vnode);
                        }
                        break;
                }
                key_put(key);
                _leave(" [pend]");
                return;
        }

        /* looks like the lock request was withdrawn on a signal */
        spin_unlock(&vnode->lock);
        _leave(" [no locks]");
}

/*
 * pass responsibility for the unlocking of a vnode on the server to the
 * manager thread, lest a pending signal in the calling thread interrupt
 * AF_RXRPC
 * - the caller must hold the vnode lock
 */
static void afs_defer_unlock(struct afs_vnode *vnode, struct key *key)
{
        cancel_delayed_work(&vnode->lock_work);
        if (!test_and_clear_bit(AFS_VNODE_READLOCKED, &vnode->flags) &&
            !test_and_clear_bit(AFS_VNODE_WRITELOCKED, &vnode->flags))
                BUG();
        if (test_and_set_bit(AFS_VNODE_UNLOCKING, &vnode->flags))
                BUG();
        vnode->unlock_key = key_get(key);
        afs_lock_may_be_available(vnode);
}

/*
 * request a lock on a file on the server
 */
static int afs_do_setlk(struct file *file, struct file_lock *fl)
{
        struct inode *inode = file_inode(file);
        struct afs_vnode *vnode = AFS_FS_I(inode);
        afs_lock_type_t type;
        struct key *key = file->private_data;
        int ret;

        _enter("{%x:%u},%u", vnode->fid.vid, vnode->fid.vnode, fl->fl_type);

        /* only whole-file locks are supported */
        if (fl->fl_start != 0 || fl->fl_end != OFFSET_MAX)
                return -EINVAL;

        ret = afs_init_lock_manager();
        if (ret < 0)
                return ret;

        fl->fl_ops = &afs_lock_ops;
        INIT_LIST_HEAD(&fl->fl_u.afs.link);
        fl->fl_u.afs.state = AFS_LOCK_PENDING;

        type = (fl->fl_type == F_RDLCK) ? AFS_LOCK_READ : AFS_LOCK_WRITE;

        spin_lock(&inode->i_lock);

        /* make sure we've got a callback on this file and that our view of the
         * data version is up to date */
        ret = afs_vnode_fetch_status(vnode, NULL, key);
        if (ret < 0)
                goto error;

        if (vnode->status.lock_count != 0 && !(fl->fl_flags & FL_SLEEP)) {
                ret = -EAGAIN;
                goto error;
        }

        spin_lock(&vnode->lock);

        /* if we've already got a readlock on the server then we can instantly
         * grant another readlock, irrespective of whether there are any
         * pending writelocks */
        if (type == AFS_LOCK_READ &&
            vnode->flags & (1 << AFS_VNODE_READLOCKED)) {
                _debug("instant readlock");
                ASSERTCMP(vnode->flags &
                          ((1 << AFS_VNODE_LOCKING) |
                           (1 << AFS_VNODE_WRITELOCKED)), ==, 0);
                ASSERT(!list_empty(&vnode->granted_locks));
                goto sharing_existing_lock;
        }

        /* if there's no-one else with a lock on this vnode, then we need to
         * ask the server for a lock */
        if (list_empty(&vnode->pending_locks) &&
            list_empty(&vnode->granted_locks)) {
                _debug("not locked");
                ASSERTCMP(vnode->flags &
                          ((1 << AFS_VNODE_LOCKING) |
                           (1 << AFS_VNODE_READLOCKED) |
                           (1 << AFS_VNODE_WRITELOCKED)), ==, 0);
                list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);
                set_bit(AFS_VNODE_LOCKING, &vnode->flags);
                spin_unlock(&vnode->lock);

                ret = afs_vnode_set_lock(vnode, key, type);
                clear_bit(AFS_VNODE_LOCKING, &vnode->flags);
                switch (ret) {
                case 0:
                        _debug("acquired");
                        goto acquired_server_lock;
                case -EWOULDBLOCK:
                        _debug("would block");
                        spin_lock(&vnode->lock);
                        ASSERT(list_empty(&vnode->granted_locks));
                        ASSERTCMP(vnode->pending_locks.next, ==,
                                  &fl->fl_u.afs.link);
                        goto wait;
                default:
                        spin_lock(&vnode->lock);
                        list_del_init(&fl->fl_u.afs.link);
                        spin_unlock(&vnode->lock);
                        goto error;
                }
        }

        /* otherwise, we need to wait for a local lock to become available */
        _debug("wait local");
        list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);
wait:
        if (!(fl->fl_flags & FL_SLEEP)) {
                _debug("noblock");
                ret = -EAGAIN;
                goto abort_attempt;
        }
        spin_unlock(&vnode->lock);

        /* now we need to sleep and wait for the lock manager thread to get the
         * lock from the server */
        _debug("sleep");
        ret = wait_event_interruptible(fl->fl_wait,
                                       fl->fl_u.afs.state <= AFS_LOCK_GRANTED);
        if (fl->fl_u.afs.state <= AFS_LOCK_GRANTED) {
                ret = fl->fl_u.afs.state;
                if (ret < 0)
                        goto error;
                spin_lock(&vnode->lock);
                goto given_lock;
        }

        /* we were interrupted, but someone may still be in the throes of
         * giving us the lock */
        _debug("intr");
        ASSERTCMP(ret, ==, -ERESTARTSYS);

        spin_lock(&vnode->lock);
        if (fl->fl_u.afs.state <= AFS_LOCK_GRANTED) {
                ret = fl->fl_u.afs.state;
                if (ret < 0) {
                        spin_unlock(&vnode->lock);
                        goto error;
                }
                goto given_lock;
        }

abort_attempt:
        /* we aren't going to get the lock, either because we're unwilling to
         * wait, or because some signal happened */
        _debug("abort");
        if (list_empty(&vnode->granted_locks) &&
            vnode->pending_locks.next == &fl->fl_u.afs.link) {
                if (vnode->pending_locks.prev != &fl->fl_u.afs.link) {
                        /* kick the next pending lock into having a go */
                        list_del_init(&fl->fl_u.afs.link);
                        afs_lock_may_be_available(vnode);
                }
        } else {
                list_del_init(&fl->fl_u.afs.link);
        }
        spin_unlock(&vnode->lock);
        goto error;

acquired_server_lock:
        /* we've acquired a server lock, but it needs to be renewed after 5
         * mins */
        spin_lock(&vnode->lock);
        afs_schedule_lock_extension(vnode);
        if (type == AFS_LOCK_READ)
                set_bit(AFS_VNODE_READLOCKED, &vnode->flags);
        else
                set_bit(AFS_VNODE_WRITELOCKED, &vnode->flags);
sharing_existing_lock:
        /* the lock has been granted as far as we're concerned... */
        fl->fl_u.afs.state = AFS_LOCK_GRANTED;
        list_move_tail(&fl->fl_u.afs.link, &vnode->granted_locks);
given_lock:
        /* ... but we do still need to get the VFS's blessing */
        ASSERT(!(vnode->flags & (1 << AFS_VNODE_LOCKING)));
        ASSERT((vnode->flags & ((1 << AFS_VNODE_READLOCKED) |
                                (1 << AFS_VNODE_WRITELOCKED))) != 0);
        ret = posix_lock_file(file, fl, NULL);
        if (ret < 0)
                goto vfs_rejected_lock;
        spin_unlock(&vnode->lock);

        /* again, make sure we've got a callback on this file and, again, make
         * sure that our view of the data version is up to date (we ignore
         * errors incurred here and deal with the consequences elsewhere) */
        afs_vnode_fetch_status(vnode, NULL, key);

error:
        spin_unlock(&inode->i_lock);
        _leave(" = %d", ret);
        return ret;

vfs_rejected_lock:
        /* the VFS rejected the lock we just obtained, so we have to discard
         * what we just got */
        _debug("vfs refused %d", ret);
        list_del_init(&fl->fl_u.afs.link);
        if (list_empty(&vnode->granted_locks))
                afs_defer_unlock(vnode, key);
        goto abort_attempt;
}

/*
 * unlock on a file on the server
 */
static int afs_do_unlk(struct file *file, struct file_lock *fl)
{
        struct afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
        struct key *key = file->private_data;
        int ret;

        _enter("{%x:%u},%u", vnode->fid.vid, vnode->fid.vnode, fl->fl_type);

        /* only whole-file unlocks are supported */
        if (fl->fl_start != 0 || fl->fl_end != OFFSET_MAX)
                return -EINVAL;

        fl->fl_ops = &afs_lock_ops;
        INIT_LIST_HEAD(&fl->fl_u.afs.link);
        fl->fl_u.afs.state = AFS_LOCK_PENDING;

        spin_lock(&vnode->lock);
        ret = posix_lock_file(file, fl, NULL);
        if (ret < 0) {
                spin_unlock(&vnode->lock);
                _leave(" = %d [vfs]", ret);
                return ret;
        }

        /* discard the server lock only if all granted locks are gone */
        if (list_empty(&vnode->granted_locks))
                afs_defer_unlock(vnode, key);
        spin_unlock(&vnode->lock);
        _leave(" = 0");
        return 0;
}

/*
 * return information about a lock we currently hold, if indeed we hold one
 */
static int afs_do_getlk(struct file *file, struct file_lock *fl)
{
        struct afs_vnode *vnode = AFS_FS_I(file->f_mapping->host);
        struct key *key = file->private_data;
        int ret, lock_count;

        _enter("");

        fl->fl_type = F_UNLCK;

        mutex_lock(&vnode->vfs_inode.i_mutex);

        /* check local lock records first */
        ret = 0;
        posix_test_lock(file, fl);
        if (fl->fl_type == F_UNLCK) {
                /* no local locks; consult the server */
                ret = afs_vnode_fetch_status(vnode, NULL, key);
                if (ret < 0)
                        goto error;
                lock_count = vnode->status.lock_count;
                if (lock_count) {
                        if (lock_count > 0)
                                fl->fl_type = F_RDLCK;
                        else
                                fl->fl_type = F_WRLCK;
                        fl->fl_start = 0;
                        fl->fl_end = OFFSET_MAX;
                }
        }

error:
        mutex_unlock(&vnode->vfs_inode.i_mutex);
        _leave(" = %d [%hd]", ret, fl->fl_type);
        return ret;
}

/*
 * manage POSIX locks on a file
 */
int afs_lock(struct file *file, int cmd, struct file_lock *fl)
{
        struct afs_vnode *vnode = AFS_FS_I(file_inode(file));

        _enter("{%x:%u},%d,{t=%x,fl=%x,r=%Ld:%Ld}",
               vnode->fid.vid, vnode->fid.vnode, cmd,
               fl->fl_type, fl->fl_flags,
               (long long) fl->fl_start, (long long) fl->fl_end);

        /* AFS doesn't support mandatory locks */
        if (__mandatory_lock(&vnode->vfs_inode) && fl->fl_type != F_UNLCK)
                return -ENOLCK;

        if (IS_GETLK(cmd))
                return afs_do_getlk(file, fl);
        if (fl->fl_type == F_UNLCK)
                return afs_do_unlk(file, fl);
        return afs_do_setlk(file, fl);
}

/*
 * manage FLOCK locks on a file
 */
int afs_flock(struct file *file, int cmd, struct file_lock *fl)
{
        struct afs_vnode *vnode = AFS_FS_I(file_inode(file));

        _enter("{%x:%u},%d,{t=%x,fl=%x}",
               vnode->fid.vid, vnode->fid.vnode, cmd,
               fl->fl_type, fl->fl_flags);

        /*
         * No BSD flocks over NFS allowed.
         * Note: we could try to fake a POSIX lock request here by
         * using ((u32) filp | 0x80000000) or some such as the pid.
         * Not sure whether that would be unique, though, or whether
         * that would break in other places.
         */
        if (!(fl->fl_flags & FL_FLOCK))
                return -ENOLCK;

        /* we're simulating flock() locks using posix locks on the server */
        if (fl->fl_type == F_UNLCK)
                return afs_do_unlk(file, fl);
        return afs_do_setlk(file, fl);
}

/*
 * the POSIX lock management core VFS code copies the lock record and adds the
 * copy into its own list, so we need to add that copy to the vnode's lock
 * queue in the same place as the original (which will be deleted shortly
 * after)
 */
static void afs_fl_copy_lock(struct file_lock *new, struct file_lock *fl)
{
        _enter("");

        list_add(&new->fl_u.afs.link, &fl->fl_u.afs.link);
}

/*
 * need to remove this lock from the vnode queue when it's removed from the
 * VFS's list
 */
static void afs_fl_release_private(struct file_lock *fl)
{
        _enter("");

        list_del_init(&fl->fl_u.afs.link);
}