/* 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

struct workqueue_struct *afs_lock_manager;

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

/*
 * 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);
                        }
                }
        }
}

/*
 * Get a lock on a file
 */
static int afs_set_lock(struct afs_vnode *vnode, struct key *key,
                        afs_lock_type_t type)
{
        struct afs_fs_cursor fc;
        int ret;

        _enter("%s{%x:%u.%u},%x,%u",
               vnode->volume->name,
               vnode->fid.vid,
               vnode->fid.vnode,
               vnode->fid.unique,
               key_serial(key), type);

        ret = -ERESTARTSYS;
        if (afs_begin_vnode_operation(&fc, vnode, key)) {
                while (afs_select_fileserver(&fc)) {
                        fc.cb_break = afs_calc_vnode_cb_break(vnode);
                        afs_fs_set_lock(&fc, type);
                }

                afs_check_for_remote_deletion(&fc, fc.vnode);
                afs_vnode_commit_status(&fc, vnode, fc.cb_break);
                ret = afs_end_vnode_operation(&fc);
        }

        _leave(" = %d", ret);
        return ret;
}

/*
 * Extend a lock on a file
 */
static int afs_extend_lock(struct afs_vnode *vnode, struct key *key)
{
        struct afs_fs_cursor fc;
        int ret;

        _enter("%s{%x:%u.%u},%x",
               vnode->volume->name,
               vnode->fid.vid,
               vnode->fid.vnode,
               vnode->fid.unique,
               key_serial(key));

        ret = -ERESTARTSYS;
        if (afs_begin_vnode_operation(&fc, vnode, key)) {
                while (afs_select_current_fileserver(&fc)) {
                        fc.cb_break = afs_calc_vnode_cb_break(vnode);
                        afs_fs_extend_lock(&fc);
                }

                afs_check_for_remote_deletion(&fc, fc.vnode);
                afs_vnode_commit_status(&fc, vnode, fc.cb_break);
                ret = afs_end_vnode_operation(&fc);
        }

        _leave(" = %d", ret);
        return ret;
}

/*
 * Release a lock on a file
 */
static int afs_release_lock(struct afs_vnode *vnode, struct key *key)
{
        struct afs_fs_cursor fc;
        int ret;

        _enter("%s{%x:%u.%u},%x",
               vnode->volume->name,
               vnode->fid.vid,
               vnode->fid.vnode,
               vnode->fid.unique,
               key_serial(key));

        ret = -ERESTARTSYS;
        if (afs_begin_vnode_operation(&fc, vnode, key)) {
                while (afs_select_current_fileserver(&fc)) {
                        fc.cb_break = afs_calc_vnode_cb_break(vnode);
                        afs_fs_release_lock(&fc);
                }

                afs_check_for_remote_deletion(&fc, fc.vnode);
                afs_vnode_commit_status(&fc, vnode, fc.cb_break);
                ret = afs_end_vnode_operation(&fc);
        }

        _leave(" = %d", ret);
        return ret;
}

/*
 * 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, *next;
        afs_lock_type_t type;
        struct key *key;
        int ret;

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

        spin_lock(&vnode->lock);

again:
        _debug("wstate %u for %p", vnode->lock_state, vnode);
        switch (vnode->lock_state) {
        case AFS_VNODE_LOCK_NEED_UNLOCK:
                _debug("unlock");
                vnode->lock_state = AFS_VNODE_LOCK_UNLOCKING;
                spin_unlock(&vnode->lock);

                /* attempt to release the server lock; if it fails, we just
                 * wait 5 minutes and it'll expire anyway */
                ret = afs_release_lock(vnode, vnode->lock_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->lock_key);
                vnode->lock_key = NULL;
                vnode->lock_state = AFS_VNODE_LOCK_NONE;

                if (list_empty(&vnode->pending_locks)) {
                        spin_unlock(&vnode->lock);
                        return;
                }

                /* The new front of the queue now owns the state variables. */
                next = list_entry(vnode->pending_locks.next,
                                  struct file_lock, fl_u.afs.link);
                vnode->lock_key = afs_file_key(next->fl_file);
                vnode->lock_type = (next->fl_type == F_RDLCK) ? AFS_LOCK_READ : AFS_LOCK_WRITE;
                vnode->lock_state = AFS_VNODE_LOCK_WAITING_FOR_CB;
                goto again;

        /* If we've already got a lock, then it must be time to extend that
         * lock as AFS locks time out after 5 minutes.
         */
        case AFS_VNODE_LOCK_GRANTED:
                _debug("extend");

                ASSERT(!list_empty(&vnode->granted_locks));

                key = key_get(vnode->lock_key);
                vnode->lock_state = AFS_VNODE_LOCK_EXTENDING;
                spin_unlock(&vnode->lock);

                ret = afs_extend_lock(vnode, key); /* RPC */
                key_put(key);

                if (ret < 0)
                        pr_warning("AFS: Failed to extend lock on {%x:%x} error %d\n",
                                   vnode->fid.vid, vnode->fid.vnode, ret);

                spin_lock(&vnode->lock);

                if (vnode->lock_state != AFS_VNODE_LOCK_EXTENDING)
                        goto again;
                vnode->lock_state = AFS_VNODE_LOCK_GRANTED;

                if (ret == 0)
                        afs_schedule_lock_extension(vnode);
                else
                        queue_delayed_work(afs_lock_manager, &vnode->lock_work,
                                           HZ * 10);
                spin_unlock(&vnode->lock);
                _leave(" [ext]");
                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.
                 */
        case AFS_VNODE_LOCK_WAITING_FOR_CB:
                _debug("get");

                key = key_get(vnode->lock_key);
                type = vnode->lock_type;
                vnode->lock_state = AFS_VNODE_LOCK_SETTING;
                spin_unlock(&vnode->lock);

                ret = afs_set_lock(vnode, key, type); /* RPC */
                key_put(key);

                spin_lock(&vnode->lock);
                switch (ret) {
                case -EWOULDBLOCK:
                        _debug("blocked");
                        break;
                case 0:
                        _debug("acquired");
                        vnode->lock_state = AFS_VNODE_LOCK_GRANTED;
                        /* Fall through */
                default:
                        /* Pass the lock or the error onto the first locker in
                         * the list - if they're looking for this type of lock.
                         * If they're not, we assume that whoever asked for it
                         * took a signal.
                         */
                        if (list_empty(&vnode->pending_locks)) {
                                _debug("withdrawn");
                                vnode->lock_state = AFS_VNODE_LOCK_NEED_UNLOCK;
                                goto again;
                        }

                        fl = list_entry(vnode->pending_locks.next,
                                        struct file_lock, fl_u.afs.link);
                        type = (fl->fl_type == F_RDLCK) ? AFS_LOCK_READ : AFS_LOCK_WRITE;
                        if (vnode->lock_type != type) {
                                _debug("changed");
                                vnode->lock_state = AFS_VNODE_LOCK_NEED_UNLOCK;
                                goto again;
                        }

                        fl->fl_u.afs.state = ret;
                        if (ret == 0)
                                afs_grant_locks(vnode, fl);
                        else
                                list_del_init(&fl->fl_u.afs.link);
                        wake_up(&fl->fl_wait);
                        spin_unlock(&vnode->lock);
                        _leave(" [granted]");
                        return;
                }

        default:
                /* Looks like a lock request was withdrawn. */
                spin_unlock(&vnode->lock);
                _leave(" [no]");
                return;
        }
}

/*
 * 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)
{
        _enter("");

        if (vnode->lock_state == AFS_VNODE_LOCK_GRANTED ||
            vnode->lock_state == AFS_VNODE_LOCK_EXTENDING) {
                cancel_delayed_work(&vnode->lock_work);

                vnode->lock_state = AFS_VNODE_LOCK_NEED_UNLOCK;
                afs_lock_may_be_available(vnode);
        }
}

/*
 * Check that our view of the file metadata is up to date and check to see
 * whether we think that we have a locking permit.
 */
static int afs_do_setlk_check(struct afs_vnode *vnode, struct key *key,
                              afs_lock_type_t type, bool can_sleep)
{
        afs_access_t access;
        int ret;

        /* Make sure we've got a callback on this file and that our view of the
         * data version is up to date.
         */
        ret = afs_validate(vnode, key);
        if (ret < 0)
                return ret;

        /* Check the permission set to see if we're actually going to be
         * allowed to get a lock on this file.
         */
        ret = afs_check_permit(vnode, key, &access);
        if (ret < 0)
                return ret;

        /* At a rough estimation, you need LOCK, WRITE or INSERT perm to
         * read-lock a file and WRITE or INSERT perm to write-lock a file.
         *
         * We can't rely on the server to do this for us since if we want to
         * share a read lock that we already have, we won't go the server.
         */
        if (type == AFS_LOCK_READ) {
                if (!(access & (AFS_ACE_INSERT | AFS_ACE_WRITE | AFS_ACE_LOCK)))
                        return -EACCES;
                if (vnode->status.lock_count == -1 && !can_sleep)
                        return -EAGAIN; /* Write locked */
        } else {
                if (!(access & (AFS_ACE_INSERT | AFS_ACE_WRITE)))
                        return -EACCES;
                if (vnode->status.lock_count != 0 && !can_sleep)
                        return -EAGAIN; /* Locked */
        }

        return 0;
}

/*
 * Remove the front runner from the pending queue.
 * - The caller must hold vnode->lock.
 */
static void afs_dequeue_lock(struct afs_vnode *vnode, struct file_lock *fl)
{
        struct file_lock *next;

        _enter("");

        /* ->lock_type, ->lock_key and ->lock_state only belong to this
         * file_lock if we're at the front of the pending queue or if we have
         * the lock granted or if the lock_state is NEED_UNLOCK or UNLOCKING.
         */
        if (vnode->granted_locks.next == &fl->fl_u.afs.link &&
            vnode->granted_locks.prev == &fl->fl_u.afs.link) {
                list_del_init(&fl->fl_u.afs.link);
                afs_defer_unlock(vnode);
                return;
        }

        if (!list_empty(&vnode->granted_locks) ||
            vnode->pending_locks.next != &fl->fl_u.afs.link) {
                list_del_init(&fl->fl_u.afs.link);
                return;
        }

        list_del_init(&fl->fl_u.afs.link);
        key_put(vnode->lock_key);
        vnode->lock_key = NULL;
        vnode->lock_state = AFS_VNODE_LOCK_NONE;

        if (list_empty(&vnode->pending_locks))
                return;

        /* The new front of the queue now owns the state variables. */
        next = list_entry(vnode->pending_locks.next,
                          struct file_lock, fl_u.afs.link);
        vnode->lock_key = afs_file_key(next->fl_file);
        vnode->lock_type = (next->fl_type == F_RDLCK) ? AFS_LOCK_READ : AFS_LOCK_WRITE;
        vnode->lock_state = AFS_VNODE_LOCK_WAITING_FOR_CB;
        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 = locks_inode(file);
        struct afs_vnode *vnode = AFS_FS_I(inode);
        afs_lock_type_t type;
        struct key *key = afs_file_key(file);
        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;

        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;

        ret = afs_do_setlk_check(vnode, key, type, fl->fl_flags & FL_SLEEP);
        if (ret < 0)
                return ret;

        spin_lock(&vnode->lock);

        /* If we've already got a readlock on the server then we instantly
         * grant another readlock, irrespective of whether there are any
         * pending writelocks.
         */
        if (type == AFS_LOCK_READ &&
            vnode->lock_state == AFS_VNODE_LOCK_GRANTED &&
            vnode->lock_type == AFS_LOCK_READ) {
                _debug("instant readlock");
                ASSERT(!list_empty(&vnode->granted_locks));
                goto share_existing_lock;
        }

        list_add_tail(&fl->fl_u.afs.link, &vnode->pending_locks);

        if (vnode->lock_state != AFS_VNODE_LOCK_NONE)
                goto need_to_wait;

        /* We don't have a lock on this vnode and we aren't currently waiting
         * for one either, so ask the server for a lock.
         *
         * Note that we need to be careful if we get interrupted by a signal
         * after dispatching the request as we may still get the lock, even
         * though we don't wait for the reply (it's not too bad a problem - the
         * lock will expire in 10 mins anyway).
         */
        _debug("not locked");
        vnode->lock_key = key_get(key);
        vnode->lock_type = type;
        vnode->lock_state = AFS_VNODE_LOCK_SETTING;
        spin_unlock(&vnode->lock);

        ret = afs_set_lock(vnode, key, type); /* RPC */

        spin_lock(&vnode->lock);
        switch (ret) {
        default:
                goto abort_attempt;

        case -EWOULDBLOCK:
                /* The server doesn't have a lock-waiting queue, so the client
                 * will have to retry.  The server will break the outstanding
                 * callbacks on a file when a lock is released.
                 */
                _debug("would block");
                ASSERT(list_empty(&vnode->granted_locks));
                ASSERTCMP(vnode->pending_locks.next, ==, &fl->fl_u.afs.link);
                vnode->lock_state = AFS_VNODE_LOCK_WAITING_FOR_CB;
                goto need_to_wait;

        case 0:
                _debug("acquired");
                break;
        }

        /* we've acquired a server lock, but it needs to be renewed after 5
         * mins */
        vnode->lock_state = AFS_VNODE_LOCK_GRANTED;
        afs_schedule_lock_extension(vnode);

share_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 */
        spin_unlock(&vnode->lock);

        ret = posix_lock_file(file, fl, NULL);
        if (ret < 0)
                goto vfs_rejected_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_validate(vnode, key);
        _leave(" = 0");
        return 0;

need_to_wait:
        /* We're going to have to wait.  Either this client doesn't have a lock
         * on the server yet and we need to wait for a callback to occur, or
         * the client does have a lock on the server, but it belongs to some
         * other process(es) and is incompatible with the lock we want.
         */
        ret = -EAGAIN;
        if (fl->fl_flags & FL_SLEEP) {
                spin_unlock(&vnode->lock);

                _debug("sleep");
                ret = wait_event_interruptible(fl->fl_wait,
                                               fl->fl_u.afs.state != AFS_LOCK_PENDING);

                spin_lock(&vnode->lock);
        }

        if (fl->fl_u.afs.state == AFS_LOCK_GRANTED)
                goto given_lock;
        if (fl->fl_u.afs.state < 0)
                ret = fl->fl_u.afs.state;

abort_attempt:
        /* we aren't going to get the lock, either because we're unwilling to
         * wait, or because some signal happened */
        _debug("abort");
        afs_dequeue_lock(vnode, fl);

error_unlock:
        spin_unlock(&vnode->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.  We defer this to the lock manager work item to
         * deal with.
         */
        _debug("vfs refused %d", ret);
        spin_lock(&vnode->lock);
        list_del_init(&fl->fl_u.afs.link);
        if (list_empty(&vnode->granted_locks))
                afs_defer_unlock(vnode);
        goto error_unlock;
}

/*
 * 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(locks_inode(file));
        int ret;

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

        /* Flush all pending writes before doing anything with locks. */
        vfs_fsync(file, 0);

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

        ret = posix_lock_file(file, fl, NULL);
        _leave(" = %d [%u]", ret, vnode->lock_state);
        return ret;
}

/*
 * 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(locks_inode(file));
        struct key *key = afs_file_key(file);
        int ret, lock_count;

        _enter("");

        fl->fl_type = F_UNLCK;

        /* check local lock records first */
        posix_test_lock(file, fl);
        if (fl->fl_type == F_UNLCK) {
                /* no local locks; consult the server */
                ret = afs_fetch_status(vnode, key, false);
                if (ret < 0)
                        goto error;

                lock_count = READ_ONCE(vnode->status.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;
        }

        ret = 0;
error:
        _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(locks_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(locks_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)
{
        struct afs_vnode *vnode = AFS_FS_I(locks_inode(fl->fl_file));

        _enter("");

        spin_lock(&vnode->lock);
        list_add(&new->fl_u.afs.link, &fl->fl_u.afs.link);
        spin_unlock(&vnode->lock);
}

/*
 * 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)
{
        struct afs_vnode *vnode = AFS_FS_I(locks_inode(fl->fl_file));

        _enter("");

        spin_lock(&vnode->lock);
        afs_dequeue_lock(vnode, fl);
        _debug("state %u for %p", vnode->lock_state, vnode);
        spin_unlock(&vnode->lock);
}