/*
 * Copyright (c) 2002, 2007 Red Hat, Inc. All rights reserved.
 *
 * This software may be freely redistributed under the terms of the
 * GNU General Public License.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * Authors: David Woodhouse <dwmw2@infradead.org>
 *          David Howells <dhowells@redhat.com>
 *
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/circ_buf.h>
#include <linux/sched.h>
#include "internal.h"

/*
 * Allow the fileserver to request callback state (re-)initialisation.
 * Unfortunately, UUIDs are not guaranteed unique.
 */
void afs_init_callback_state(struct afs_server *server)
{
        rcu_read_lock();
        do {
                server->cb_s_break++;
                server = rcu_dereference(server->uuid_next);
        } while (0);
        rcu_read_unlock();
}

/*
 * actually break a callback
 */
void __afs_break_callback(struct afs_vnode *vnode, enum afs_cb_break_reason reason)
{
        _enter("");

        clear_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags);
        if (test_and_clear_bit(AFS_VNODE_CB_PROMISED, &vnode->flags)) {
                vnode->cb_break++;
                afs_clear_permits(vnode);

                if (vnode->lock_state == AFS_VNODE_LOCK_WAITING_FOR_CB)
                        afs_lock_may_be_available(vnode);

                trace_afs_cb_break(&vnode->fid, vnode->cb_break, reason, true);
        } else {
                trace_afs_cb_break(&vnode->fid, vnode->cb_break, reason, false);
        }
}

void afs_break_callback(struct afs_vnode *vnode, enum afs_cb_break_reason reason)
{
        write_seqlock(&vnode->cb_lock);
        __afs_break_callback(vnode, reason);
        write_sequnlock(&vnode->cb_lock);
}

/*
 * Look up a volume by volume ID under RCU conditions.
 */
static struct afs_volume *afs_lookup_volume_rcu(struct afs_cell *cell,
                                                afs_volid_t vid)
{
        struct afs_volume *volume = NULL;
        struct rb_node *p;
        int seq = 0;

        do {
                /* Unfortunately, rbtree walking doesn't give reliable results
                 * under just the RCU read lock, so we have to check for
                 * changes.
                 */
                read_seqbegin_or_lock(&cell->volume_lock, &seq);

                p = rcu_dereference_raw(cell->volumes.rb_node);
                while (p) {
                        volume = rb_entry(p, struct afs_volume, cell_node);

                        if (volume->vid < vid)
                                p = rcu_dereference_raw(p->rb_left);
                        else if (volume->vid > vid)
                                p = rcu_dereference_raw(p->rb_right);
                        else
                                break;
                        volume = NULL;
                }

        } while (need_seqretry(&cell->volume_lock, seq));

        done_seqretry(&cell->volume_lock, seq);
        return volume;
}

/*
 * allow the fileserver to explicitly break one callback
 * - happens when
 *   - the backing file is changed
 *   - a lock is released
 */
static void afs_break_one_callback(struct afs_volume *volume,
                                   struct afs_fid *fid)
{
        struct super_block *sb;
        struct afs_vnode *vnode;
        struct inode *inode;

        if (fid->vnode == 0 && fid->unique == 0) {
                /* The callback break applies to an entire volume. */
                write_lock(&volume->cb_v_break_lock);
                volume->cb_v_break++;
                trace_afs_cb_break(fid, volume->cb_v_break,
                                   afs_cb_break_for_volume_callback, false);
                write_unlock(&volume->cb_v_break_lock);
                return;
        }

        /* See if we can find a matching inode - even an I_NEW inode needs to
         * be marked as it can have its callback broken before we finish
         * setting up the local inode.
         */
        sb = rcu_dereference(volume->sb);
        if (!sb)
                return;

        inode = find_inode_rcu(sb, fid->vnode, afs_ilookup5_test_by_fid, fid);
        if (inode) {
                vnode = AFS_FS_I(inode);
                afs_break_callback(vnode, afs_cb_break_for_callback);
        } else {
                trace_afs_cb_miss(fid, afs_cb_break_for_callback);
        }
}

static void afs_break_some_callbacks(struct afs_server *server,
                                     struct afs_callback_break *cbb,
                                     size_t *_count)
{
        struct afs_callback_break *residue = cbb;
        struct afs_volume *volume;
        afs_volid_t vid = cbb->fid.vid;
        size_t i;

        volume = afs_lookup_volume_rcu(server->cell, vid);

        /* TODO: Find all matching volumes if we couldn't match the server and
         * break them anyway.
         */

        for (i = *_count; i > 0; cbb++, i--) {
                if (cbb->fid.vid == vid) {
                        _debug("- Fid { vl=%08llx n=%llu u=%u }",
                               cbb->fid.vid,
                               cbb->fid.vnode,
                               cbb->fid.unique);
                        --*_count;
                        if (volume)
                                afs_break_one_callback(volume, &cbb->fid);
                } else {
                        *residue++ = *cbb;
                }
        }
}

/*
 * allow the fileserver to break callback promises
 */
void afs_break_callbacks(struct afs_server *server, size_t count,
                         struct afs_callback_break *callbacks)
{
        _enter("%p,%zu,", server, count);

        ASSERT(server != NULL);

        rcu_read_lock();

        while (count > 0)
                afs_break_some_callbacks(server, callbacks, &count);

        rcu_read_unlock();
        return;
}