/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * dcache.c
 *
 * dentry cache handling code
 *
 * Copyright (C) 2002, 2004 Oracle.  All rights reserved.
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * 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., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/fs.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/namei.h>

#define MLOG_MASK_PREFIX ML_DCACHE
#include <cluster/masklog.h>

#include "ocfs2.h"

#include "alloc.h"
#include "dcache.h"
#include "dlmglue.h"
#include "file.h"
#include "inode.h"


static int ocfs2_dentry_revalidate(struct dentry *dentry,
                                   struct nameidata *nd)
{
        struct inode *inode = dentry->d_inode;
        int ret = 0;    /* if all else fails, just return false */
        struct ocfs2_super *osb = OCFS2_SB(dentry->d_sb);

        mlog_entry("(0x%p, '%.*s')\n", dentry,
                   dentry->d_name.len, dentry->d_name.name);

        /* Never trust a negative dentry - force a new lookup. */
        if (inode == NULL) {
                mlog(0, "negative dentry: %.*s\n", dentry->d_name.len,
                     dentry->d_name.name);
                goto bail;
        }

        BUG_ON(!osb);

        if (inode == osb->root_inode || is_bad_inode(inode))
                goto bail;

        spin_lock(&OCFS2_I(inode)->ip_lock);
        /* did we or someone else delete this inode? */
        if (OCFS2_I(inode)->ip_flags & OCFS2_INODE_DELETED) {
                spin_unlock(&OCFS2_I(inode)->ip_lock);
                mlog(0, "inode (%llu) deleted, returning false\n",
                     (unsigned long long)OCFS2_I(inode)->ip_blkno);
                goto bail;
        }
        spin_unlock(&OCFS2_I(inode)->ip_lock);

        /*
         * We don't need a cluster lock to test this because once an
         * inode nlink hits zero, it never goes back.
         */
        if (inode->i_nlink == 0) {
                mlog(0, "Inode %llu orphaned, returning false "
                     "dir = %d\n",
                     (unsigned long long)OCFS2_I(inode)->ip_blkno,
                     S_ISDIR(inode->i_mode));
                goto bail;
        }

        ret = 1;

bail:
        mlog_exit(ret);

        return ret;
}

static int ocfs2_match_dentry(struct dentry *dentry,
                              u64 parent_blkno,
                              int skip_unhashed)
{
        struct inode *parent;

        /*
         * ocfs2_lookup() does a d_splice_alias() _before_ attaching
         * to the lock data, so we skip those here, otherwise
         * ocfs2_dentry_attach_lock() will get its original dentry
         * back.
         */
        if (!dentry->d_fsdata)
                return 0;

        if (!dentry->d_parent)
                return 0;

        if (skip_unhashed && d_unhashed(dentry))
                return 0;

        parent = dentry->d_parent->d_inode;
        /* Negative parent dentry? */
        if (!parent)
                return 0;

        /* Name is in a different directory. */
        if (OCFS2_I(parent)->ip_blkno != parent_blkno)
                return 0;

        return 1;
}

/*
 * Walk the inode alias list, and find a dentry which has a given
 * parent. ocfs2_dentry_attach_lock() wants to find _any_ alias as it
 * is looking for a dentry_lock reference. The vote thread is looking
 * to unhash aliases, so we allow it to skip any that already have
 * that property.
 */
struct dentry *ocfs2_find_local_alias(struct inode *inode,
                                      u64 parent_blkno,
                                      int skip_unhashed)
{
        struct list_head *p;
        struct dentry *dentry = NULL;

        spin_lock(&dcache_lock);

        list_for_each(p, &inode->i_dentry) {
                dentry = list_entry(p, struct dentry, d_alias);

                if (ocfs2_match_dentry(dentry, parent_blkno, skip_unhashed)) {
                        mlog(0, "dentry found: %.*s\n",
                             dentry->d_name.len, dentry->d_name.name);

                        dget_locked(dentry);
                        break;
                }

                dentry = NULL;
        }

        spin_unlock(&dcache_lock);

        return dentry;
}

DEFINE_SPINLOCK(dentry_attach_lock);

/*
 * Attach this dentry to a cluster lock.
 *
 * Dentry locks cover all links in a given directory to a particular
 * inode. We do this so that ocfs2 can build a lock name which all
 * nodes in the cluster can agree on at all times. Shoving full names
 * in the cluster lock won't work due to size restrictions. Covering
 * links inside of a directory is a good compromise because it still
 * allows us to use the parent directory lock to synchronize
 * operations.
 *
 * Call this function with the parent dir semaphore and the parent dir
 * cluster lock held.
 *
 * The dir semaphore will protect us from having to worry about
 * concurrent processes on our node trying to attach a lock at the
 * same time.
 *
 * The dir cluster lock (held at either PR or EX mode) protects us
 * from unlink and rename on other nodes.
 *
 * A dput() can happen asynchronously due to pruning, so we cover
 * attaching and detaching the dentry lock with a
 * dentry_attach_lock.
 *
 * A node which has done lookup on a name retains a protected read
 * lock until final dput. If the user requests and unlink or rename,
 * the protected read is upgraded to an exclusive lock. Other nodes
 * who have seen the dentry will then be informed that they need to
 * downgrade their lock, which will involve d_delete on the
 * dentry. This happens in ocfs2_dentry_convert_worker().
 */
int ocfs2_dentry_attach_lock(struct dentry *dentry,
                             struct inode *inode,
                             u64 parent_blkno)
{
        int ret;
        struct dentry *alias;
        struct ocfs2_dentry_lock *dl = dentry->d_fsdata;

        mlog(0, "Attach \"%.*s\", parent %llu, fsdata: %p\n",
             dentry->d_name.len, dentry->d_name.name,
             (unsigned long long)parent_blkno, dl);

        /*
         * Negative dentry. We ignore these for now.
         *
         * XXX: Could we can improve ocfs2_dentry_revalidate() by
         * tracking these?
         */
        if (!inode)
                return 0;

        if (dl) {
                mlog_bug_on_msg(dl->dl_parent_blkno != parent_blkno,
                                " \"%.*s\": old parent: %llu, new: %llu\n",
                                dentry->d_name.len, dentry->d_name.name,
                                (unsigned long long)parent_blkno,
                                (unsigned long long)dl->dl_parent_blkno);
                return 0;
        }

        alias = ocfs2_find_local_alias(inode, parent_blkno, 0);
        if (alias) {
                /*
                 * Great, an alias exists, which means we must have a
                 * dentry lock already. We can just grab the lock off
                 * the alias and add it to the list.
                 *
                 * We're depending here on the fact that this dentry
                 * was found and exists in the dcache and so must have
                 * a reference to the dentry_lock because we can't
                 * race creates. Final dput() cannot happen on it
                 * since we have it pinned, so our reference is safe.
                 */
                dl = alias->d_fsdata;
                mlog_bug_on_msg(!dl, "parent %llu, ino %llu\n",
                                (unsigned long long)parent_blkno,
                                (unsigned long long)OCFS2_I(inode)->ip_blkno);

                mlog_bug_on_msg(dl->dl_parent_blkno != parent_blkno,
                                " \"%.*s\": old parent: %llu, new: %llu\n",
                                dentry->d_name.len, dentry->d_name.name,
                                (unsigned long long)parent_blkno,
                                (unsigned long long)dl->dl_parent_blkno);

                mlog(0, "Found: %s\n", dl->dl_lockres.l_name);

                goto out_attach;
        }

        /*
         * There are no other aliases
         */
        dl = kmalloc(sizeof(*dl), GFP_NOFS);
        if (!dl) {
                ret = -ENOMEM;
                mlog_errno(ret);
                return ret;
        }

        dl->dl_count = 0;
        /*
         * Does this have to happen below, for all attaches, in case
         * the struct inode gets blown away by votes?
         */
        dl->dl_inode = igrab(inode);
        dl->dl_parent_blkno = parent_blkno;
        ocfs2_dentry_lock_res_init(dl, parent_blkno, inode);

out_attach:
        spin_lock(&dentry_attach_lock);
        dentry->d_fsdata = dl;
        dl->dl_count++;
        spin_unlock(&dentry_attach_lock);

        /*
         * This actually gets us our PRMODE level lock. From now on,
         * we'll have a notification if one of these names is
         * destroyed on another node.
         */
        ret = ocfs2_dentry_lock(dentry, 0);
        if (!ret)
                ocfs2_dentry_unlock(dentry, 0);
        else
                mlog_errno(ret);

        dput(alias);

        return ret;
}

/*
 * ocfs2_dentry_iput() and friends.
 *
 * At this point, our particular dentry is detached from the inodes
 * alias list, so there's no way that the locking code can find it.
 *
 * The interesting stuff happens when we determine that our lock needs
 * to go away because this is the last subdir alias in the
 * system. This function needs to handle a couple things:
 *
 * 1) Synchronizing lock shutdown with the downconvert threads. This
 *    is already handled for us via the lockres release drop function
 *    called in ocfs2_release_dentry_lock()
 *
 * 2) A race may occur when we're doing our lock shutdown and
 *    another process wants to create a new dentry lock. Right now we
 *    let them race, which means that for a very short while, this
 *    node might have two locks on a lock resource. This should be a
 *    problem though because one of them is in the process of being
 *    thrown out.
 */
static void ocfs2_drop_dentry_lock(struct ocfs2_super *osb,
                                   struct ocfs2_dentry_lock *dl)
{
        iput(dl->dl_inode);
        ocfs2_simple_drop_lockres(osb, &dl->dl_lockres);
        ocfs2_lock_res_free(&dl->dl_lockres);
        kfree(dl);
}

void ocfs2_dentry_lock_put(struct ocfs2_super *osb,
                           struct ocfs2_dentry_lock *dl)
{
        int unlock = 0;

        BUG_ON(dl->dl_count == 0);

        spin_lock(&dentry_attach_lock);
        dl->dl_count--;
        unlock = !dl->dl_count;
        spin_unlock(&dentry_attach_lock);

        if (unlock)
                ocfs2_drop_dentry_lock(osb, dl);
}

static void ocfs2_dentry_iput(struct dentry *dentry, struct inode *inode)
{
        struct ocfs2_dentry_lock *dl = dentry->d_fsdata;

        if (!dl) {
                /*
                 * No dentry lock is ok if we're disconnected or
                 * unhashed.
                 */
                if (!(dentry->d_flags & DCACHE_DISCONNECTED) &&
                    !d_unhashed(dentry)) {
                        unsigned long long ino = 0ULL;
                        if (inode)
                                ino = (unsigned long long)OCFS2_I(inode)->ip_blkno;
                        mlog(ML_ERROR, "Dentry is missing cluster lock. "
                             "inode: %llu, d_flags: 0x%x, d_name: %.*s\n",
                             ino, dentry->d_flags, dentry->d_name.len,
                             dentry->d_name.name);
                }

                goto out;
        }

        mlog_bug_on_msg(dl->dl_count == 0, "dentry: %.*s, count: %u\n",
                        dentry->d_name.len, dentry->d_name.name,
                        dl->dl_count);

        ocfs2_dentry_lock_put(OCFS2_SB(dentry->d_sb), dl);

out:
        iput(inode);
}

/*
 * d_move(), but keep the locks in sync.
 *
 * When we are done, "dentry" will have the parent dir and name of
 * "target", which will be thrown away.
 *
 * We manually update the lock of "dentry" if need be.
 *
 * "target" doesn't have it's dentry lock touched - we allow the later
 * dput() to handle this for us.
 *
 * This is called during ocfs2_rename(), while holding parent
 * directory locks. The dentries have already been deleted on other
 * nodes via ocfs2_remote_dentry_delete().
 *
 * Normally, the VFS handles the d_move() for the file system, after
 * the ->rename() callback. OCFS2 wants to handle this internally, so
 * the new lock can be created atomically with respect to the cluster.
 */
void ocfs2_dentry_move(struct dentry *dentry, struct dentry *target,
                       struct inode *old_dir, struct inode *new_dir)
{
        int ret;
        struct ocfs2_super *osb = OCFS2_SB(old_dir->i_sb);
        struct inode *inode = dentry->d_inode;

        /*
         * Move within the same directory, so the actual lock info won't
         * change.
         *
         * XXX: Is there any advantage to dropping the lock here?
         */
        if (old_dir == new_dir)
                goto out_move;

        ocfs2_dentry_lock_put(osb, dentry->d_fsdata);

        dentry->d_fsdata = NULL;
        ret = ocfs2_dentry_attach_lock(dentry, inode, OCFS2_I(new_dir)->ip_blkno);
        if (ret)
                mlog_errno(ret);

out_move:
        d_move(dentry, target);
}

struct dentry_operations ocfs2_dentry_ops = {
        .d_revalidate           = ocfs2_dentry_revalidate,
        .d_iput                 = ocfs2_dentry_iput,
};