/*
 * 2007+ Copyright (c) Evgeniy Polyakov <zbr@ioremap.net>
 * 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.
 */

#include <linux/module.h>
#include <linux/backing-dev.h>
#include <linux/crypto.h>
#include <linux/fs.h>
#include <linux/jhash.h>
#include <linux/hash.h>
#include <linux/ktime.h>
#include <linux/mm.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/parser.h>
#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/statfs.h>
#include <linux/writeback.h>

#include "netfs.h"

#define POHMELFS_MAGIC_NUM      0x504f482e

static struct kmem_cache *pohmelfs_inode_cache;
static atomic_t psb_bdi_num = ATOMIC_INIT(0);

/*
 * Removes inode from all trees, drops local name cache and removes all queued
 * requests for object removal.
 */
void pohmelfs_inode_del_inode(struct pohmelfs_sb *psb, struct pohmelfs_inode *pi)
{
        mutex_lock(&pi->offset_lock);
        pohmelfs_free_names(pi);
        mutex_unlock(&pi->offset_lock);

        dprintk("%s: deleted stuff in ino: %llu.\n", __func__, pi->ino);
}

/*
 * Sync inode to server.
 * Returns zero in success and negative error value otherwise.
 * It will gather path to root directory into structures containing
 * creation mode, permissions and names, so that the whole path
 * to given inode could be created using only single network command.
 */
int pohmelfs_write_inode_create(struct inode *inode, struct netfs_trans *trans)
{
        struct pohmelfs_inode *pi = POHMELFS_I(inode);
        int err = -ENOMEM, size;
        struct netfs_cmd *cmd;
        void *data;
        int cur_len = netfs_trans_cur_len(trans);

        if (unlikely(cur_len < 0))
                return -ETOOSMALL;

        cmd = netfs_trans_current(trans);
        cur_len -= sizeof(struct netfs_cmd);

        data = (void *)(cmd + 1);

        err = pohmelfs_construct_path_string(pi, data, cur_len);
        if (err < 0)
                goto err_out_exit;

        size = err;

        cmd->start = i_size_read(inode);
        cmd->cmd = NETFS_CREATE;
        cmd->size = size;
        cmd->id = pi->ino;
        cmd->ext = inode->i_mode;

        netfs_convert_cmd(cmd);

        netfs_trans_update(cmd, trans, size);

        return 0;

err_out_exit:
        printk("%s: completed ino: %llu, err: %d.\n", __func__, pi->ino, err);
        return err;
}

static int pohmelfs_write_trans_complete(struct page **pages, unsigned int page_num,
                void *private, int err)
{
        unsigned i;

        dprintk("%s: pages: %lu-%lu, page_num: %u, err: %d.\n",
                        __func__, pages[0]->index, pages[page_num-1]->index,
                        page_num, err);

        for (i = 0; i < page_num; i++) {
                struct page *page = pages[i];

                if (!page)
                        continue;

                end_page_writeback(page);

                if (err < 0) {
                        SetPageError(page);
                        set_page_dirty(page);
                }

                unlock_page(page);
                page_cache_release(page);

                /* dprintk("%s: %3u/%u: page: %p.\n", __func__, i, page_num, page); */
        }
        return err;
}

static int pohmelfs_inode_has_dirty_pages(struct address_space *mapping, pgoff_t index)
{
        int ret;
        struct page *page;

        rcu_read_lock();
        ret = radix_tree_gang_lookup_tag(&mapping->page_tree,
                                (void **)&page, index, 1, PAGECACHE_TAG_DIRTY);
        rcu_read_unlock();
        return ret;
}

static int pohmelfs_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
        struct inode *inode = mapping->host;
        struct pohmelfs_inode *pi = POHMELFS_I(inode);
        struct pohmelfs_sb *psb = POHMELFS_SB(inode->i_sb);
        int err = 0;
        int done = 0;
        int nr_pages;
        pgoff_t index;
        pgoff_t end;            /* Inclusive */
        int scanned = 0;
        int range_whole = 0;

        if (wbc->range_cyclic) {
                index = mapping->writeback_index; /* Start from prev offset */
                end = -1;
        } else {
                index = wbc->range_start >> PAGE_CACHE_SHIFT;
                end = wbc->range_end >> PAGE_CACHE_SHIFT;
                if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
                        range_whole = 1;
                scanned = 1;
        }
retry:
        while (!done && (index <= end)) {
                unsigned int i = min(end - index, (pgoff_t)psb->trans_max_pages);
                int path_len;
                struct netfs_trans *trans;

                err = pohmelfs_inode_has_dirty_pages(mapping, index);
                if (!err)
                        break;

                err = pohmelfs_path_length(pi);
                if (err < 0)
                        break;

                path_len = err;

                if (path_len <= 2) {
                        err = -ENOENT;
                        break;
                }

                trans = netfs_trans_alloc(psb, path_len, 0, i);
                if (!trans) {
                        err = -ENOMEM;
                        break;
                }
                trans->complete = &pohmelfs_write_trans_complete;

                trans->page_num = nr_pages = find_get_pages_tag(mapping, &index,
                                PAGECACHE_TAG_DIRTY, trans->page_num,
                                trans->pages);

                dprintk("%s: t: %p, nr_pages: %u, end: %lu, index: %lu, max: %u.\n",
                                __func__, trans, nr_pages, end, index, trans->page_num);

                if (!nr_pages)
                        goto err_out_reset;

                err = pohmelfs_write_inode_create(inode, trans);
                if (err)
                        goto err_out_reset;

                err = 0;
                scanned = 1;

                for (i = 0; i < trans->page_num; i++) {
                        struct page *page = trans->pages[i];

                        lock_page(page);

                        if (unlikely(page->mapping != mapping))
                                goto out_continue;

                        if (!wbc->range_cyclic && page->index > end) {
                                done = 1;
                                goto out_continue;
                        }

                        if (wbc->sync_mode != WB_SYNC_NONE)
                                wait_on_page_writeback(page);

                        if (PageWriteback(page) ||
                            !clear_page_dirty_for_io(page)) {
                                dprintk("%s: not clear for io page: %p, writeback: %d.\n",
                                                __func__, page, PageWriteback(page));
                                goto out_continue;
                        }

                        set_page_writeback(page);

                        trans->attached_size += page_private(page);
                        trans->attached_pages++;
#if 0
                        dprintk("%s: %u/%u added trans: %p, gen: %u, page: %p, [High: %d], size: %lu, idx: %lu.\n",
                                        __func__, i, trans->page_num, trans, trans->gen, page,
                                        !!PageHighMem(page), page_private(page), page->index);
#endif
                        wbc->nr_to_write--;

                        if (wbc->nr_to_write <= 0)
                                done = 1;

                        continue;
out_continue:
                        unlock_page(page);
                        trans->pages[i] = NULL;
                }

                err = netfs_trans_finish(trans, psb);
                if (err)
                        break;

                continue;

err_out_reset:
                trans->result = err;
                netfs_trans_reset(trans);
                netfs_trans_put(trans);
                break;
        }

        if (!scanned && !done) {
                /*
                 * We hit the last page and there is more work to be done: wrap
                 * back to the start of the file
                 */
                scanned = 1;
                index = 0;
                goto retry;
        }

        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
                mapping->writeback_index = index;

        return err;
}

/*
 * Inode writeback creation completion callback.
 * Only invoked for just created inodes, which do not have pages attached,
 * like dirs and empty files.
 */
static int pohmelfs_write_inode_complete(struct page **pages, unsigned int page_num,
                void *private, int err)
{
        struct inode *inode = private;
        struct pohmelfs_inode *pi = POHMELFS_I(inode);

        if (inode) {
                if (err) {
                        mark_inode_dirty(inode);
                        clear_bit(NETFS_INODE_REMOTE_SYNCED, &pi->state);
                } else {
                        set_bit(NETFS_INODE_REMOTE_SYNCED, &pi->state);
                }

                pohmelfs_put_inode(pi);
        }

        return err;
}

int pohmelfs_write_create_inode(struct pohmelfs_inode *pi)
{
        struct netfs_trans *t;
        struct inode *inode = &pi->vfs_inode;
        struct pohmelfs_sb *psb = POHMELFS_SB(inode->i_sb);
        int err;

        if (test_bit(NETFS_INODE_REMOTE_SYNCED, &pi->state))
                return 0;

        dprintk("%s: started ino: %llu.\n", __func__, pi->ino);

        err = pohmelfs_path_length(pi);
        if (err < 0)
                goto err_out_exit;

        t = netfs_trans_alloc(psb, err + 1, 0, 0);
        if (!t) {
                err = -ENOMEM;
                goto err_out_exit;
        }
        t->complete = pohmelfs_write_inode_complete;
        t->private = igrab(inode);
        if (!t->private) {
                err = -ENOENT;
                goto err_out_put;
        }

        err = pohmelfs_write_inode_create(inode, t);
        if (err)
                goto err_out_put;

        netfs_trans_finish(t, POHMELFS_SB(inode->i_sb));

        return 0;

err_out_put:
        t->result = err;
        netfs_trans_put(t);
err_out_exit:
        return err;
}

/*
 * Sync all not-yet-created children in given directory to the server.
 */
static int pohmelfs_write_inode_create_children(struct inode *inode)
{
        struct pohmelfs_inode *parent = POHMELFS_I(inode);
        struct super_block *sb = inode->i_sb;
        struct pohmelfs_name *n;

        while (!list_empty(&parent->sync_create_list)) {
                n = NULL;
                mutex_lock(&parent->offset_lock);
                if (!list_empty(&parent->sync_create_list)) {
                        n = list_first_entry(&parent->sync_create_list,
                                struct pohmelfs_name, sync_create_entry);
                        list_del_init(&n->sync_create_entry);
                }
                mutex_unlock(&parent->offset_lock);

                if (!n)
                        break;

                inode = ilookup(sb, n->ino);

                dprintk("%s: parent: %llu, ino: %llu, inode: %p.\n",
                                __func__, parent->ino, n->ino, inode);

                if (inode && (inode->i_state & I_DIRTY)) {
                        struct pohmelfs_inode *pi = POHMELFS_I(inode);
                        pohmelfs_write_create_inode(pi);
                        /* pohmelfs_meta_command(pi, NETFS_INODE_INFO, 0, NULL, NULL, 0); */
                        iput(inode);
                }
        }

        return 0;
}

/*
 * Removes given child from given inode on server.
 */
int pohmelfs_remove_child(struct pohmelfs_inode *pi, struct pohmelfs_name *n)
{
        return pohmelfs_meta_command_data(pi, pi->ino, NETFS_REMOVE, NULL, 0, NULL, NULL, 0);
}

/*
 * Writeback for given inode.
 */
static int pohmelfs_write_inode(struct inode *inode,
                                struct writeback_control *wbc)
{
        struct pohmelfs_inode *pi = POHMELFS_I(inode);

        pohmelfs_write_create_inode(pi);
        pohmelfs_write_inode_create_children(inode);

        return 0;
}

/*
 * It is not exported, sorry...
 */
static inline wait_queue_head_t *page_waitqueue(struct page *page)
{
        const struct zone *zone = page_zone(page);

        return &zone->wait_table[hash_ptr(page, zone->wait_table_bits)];
}

static int pohmelfs_wait_on_page_locked(struct page *page)
{
        struct pohmelfs_sb *psb = POHMELFS_SB(page->mapping->host->i_sb);
        long ret = psb->wait_on_page_timeout;
        DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
        int err = 0;

        if (!PageLocked(page))
                return 0;

        for (;;) {
                prepare_to_wait(page_waitqueue(page),
                                &wait.wait, TASK_INTERRUPTIBLE);

                dprintk("%s: page: %p, locked: %d, uptodate: %d, error: %d, flags: %lx.\n",
                                __func__, page, PageLocked(page), PageUptodate(page),
                                PageError(page), page->flags);

                if (!PageLocked(page))
                        break;

                if (!signal_pending(current)) {
                        ret = schedule_timeout(ret);
                        if (!ret)
                                break;
                        continue;
                }
                ret = -ERESTARTSYS;
                break;
        }
        finish_wait(page_waitqueue(page), &wait.wait);

        if (!ret)
                err = -ETIMEDOUT;


        if (!err)
                SetPageUptodate(page);

        if (err)
                printk("%s: page: %p, uptodate: %d, locked: %d, err: %d.\n",
                        __func__, page, PageUptodate(page), PageLocked(page), err);

        return err;
}

static int pohmelfs_read_page_complete(struct page **pages, unsigned int page_num,
                void *private, int err)
{
        struct page *page = private;

        if (PageChecked(page))
                return err;

        if (err < 0) {
                dprintk("%s: page: %p, err: %d.\n", __func__, page, err);
                SetPageError(page);
        }

        unlock_page(page);

        return err;
}

/*
 * Read a page from remote server.
 * Function will wait until page is unlocked.
 */
static int pohmelfs_readpage(struct file *file, struct page *page)
{
        struct inode *inode = page->mapping->host;
        struct pohmelfs_sb *psb = POHMELFS_SB(inode->i_sb);
        struct pohmelfs_inode *pi = POHMELFS_I(inode);
        struct netfs_trans *t;
        struct netfs_cmd *cmd;
        int err, path_len;
        void *data;
        u64 isize;

        err = pohmelfs_data_lock(pi, page->index << PAGE_CACHE_SHIFT,
                        PAGE_SIZE, POHMELFS_READ_LOCK);
        if (err)
                goto err_out_exit;

        isize = i_size_read(inode);
        if (isize <= page->index << PAGE_CACHE_SHIFT) {
                SetPageUptodate(page);
                unlock_page(page);
                return 0;
        }

        path_len = pohmelfs_path_length(pi);
        if (path_len < 0) {
                err = path_len;
                goto err_out_exit;
        }

        t = netfs_trans_alloc(psb, path_len, NETFS_TRANS_SINGLE_DST, 0);
        if (!t) {
                err = -ENOMEM;
                goto err_out_exit;
        }

        t->complete = pohmelfs_read_page_complete;
        t->private = page;

        cmd = netfs_trans_current(t);
        data = (void *)(cmd + 1);

        err = pohmelfs_construct_path_string(pi, data, path_len);
        if (err < 0)
                goto err_out_free;

        path_len = err;

        cmd->id = pi->ino;
        cmd->start = page->index;
        cmd->start <<= PAGE_CACHE_SHIFT;
        cmd->size = PAGE_CACHE_SIZE + path_len;
        cmd->cmd = NETFS_READ_PAGE;
        cmd->ext = path_len;

        dprintk("%s: path: '%s', page: %p, ino: %llu, start: %llu, size: %lu.\n",
                        __func__, (char *)data, page, pi->ino, cmd->start, PAGE_CACHE_SIZE);

        netfs_convert_cmd(cmd);
        netfs_trans_update(cmd, t, path_len);

        err = netfs_trans_finish(t, psb);
        if (err)
                goto err_out_return;

        return pohmelfs_wait_on_page_locked(page);

err_out_free:
        t->result = err;
        netfs_trans_put(t);
err_out_exit:
        SetPageError(page);
        if (PageLocked(page))
                unlock_page(page);
err_out_return:
        printk("%s: page: %p, start: %lu, size: %lu, err: %d.\n",
                __func__, page, page->index << PAGE_CACHE_SHIFT, PAGE_CACHE_SIZE, err);

        return err;
}

/*
 * Write begin/end magic.
 * Allocates a page and writes inode if it was not synced to server before.
 */
static int pohmelfs_write_begin(struct file *file, struct address_space *mapping,
                loff_t pos, unsigned len, unsigned flags,
                struct page **pagep, void **fsdata)
{
        struct inode *inode = mapping->host;
        struct page *page;
        pgoff_t index;
        unsigned start, end;
        int err;

        *pagep = NULL;

        index = pos >> PAGE_CACHE_SHIFT;
        start = pos & (PAGE_CACHE_SIZE - 1);
        end = start + len;

        page = grab_cache_page(mapping, index);
#if 0
        dprintk("%s: page: %p pos: %llu, len: %u, index: %lu, start: %u, end: %u, uptodate: %d.\n",
                        __func__, page, pos, len, index, start, end, PageUptodate(page));
#endif
        if (!page) {
                err = -ENOMEM;
                goto err_out_exit;
        }

        while (!PageUptodate(page)) {
                if (start && test_bit(NETFS_INODE_REMOTE_SYNCED, &POHMELFS_I(inode)->state)) {
                        err = pohmelfs_readpage(file, page);
                        if (err)
                                goto err_out_exit;

                        lock_page(page);
                        continue;
                }

                if (len != PAGE_CACHE_SIZE) {
                        void *kaddr = kmap_atomic(page, KM_USER0);

                        memset(kaddr + start, 0, PAGE_CACHE_SIZE - start);
                        flush_dcache_page(page);
                        kunmap_atomic(kaddr, KM_USER0);
                }
                SetPageUptodate(page);
        }

        set_page_private(page, end);

        *pagep = page;

        return 0;

err_out_exit:
        page_cache_release(page);
        *pagep = NULL;

        return err;
}

static int pohmelfs_write_end(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned copied,
                        struct page *page, void *fsdata)
{
        struct inode *inode = mapping->host;

        if (copied != len) {
                unsigned from = pos & (PAGE_CACHE_SIZE - 1);
                void *kaddr = kmap_atomic(page, KM_USER0);

                memset(kaddr + from + copied, 0, len - copied);
                flush_dcache_page(page);
                kunmap_atomic(kaddr, KM_USER0);
        }

        SetPageUptodate(page);
        set_page_dirty(page);
#if 0
        dprintk("%s: page: %p [U: %d, D: %d, L: %d], pos: %llu, len: %u, copied: %u.\n",
                        __func__, page,
                        PageUptodate(page), PageDirty(page), PageLocked(page),
                        pos, len, copied);
#endif
        flush_dcache_page(page);

        unlock_page(page);
        page_cache_release(page);

        if (pos + copied > inode->i_size) {
                struct pohmelfs_sb *psb = POHMELFS_SB(inode->i_sb);

                psb->avail_size -= pos + copied - inode->i_size;

                i_size_write(inode, pos + copied);
        }

        return copied;
}

static int pohmelfs_readpages_trans_complete(struct page **__pages, unsigned int page_num,
                void *private, int err)
{
        struct pohmelfs_inode *pi = private;
        unsigned int i, num;
        struct page **pages, *page = (struct page *)__pages;
        loff_t index = page->index;

        pages = kzalloc(sizeof(void *) * page_num, GFP_NOIO);
        if (!pages)
                return -ENOMEM;

        num = find_get_pages_contig(pi->vfs_inode.i_mapping, index, page_num, pages);
        if (num <= 0) {
                err = num;
                goto err_out_free;
        }

        for (i = 0; i < num; ++i) {
                page = pages[i];

                if (err)
                        printk("%s: %u/%u: page: %p, index: %lu, uptodate: %d, locked: %d, err: %d.\n",
                                __func__, i, num, page, page->index,
                                PageUptodate(page), PageLocked(page), err);

                if (!PageChecked(page)) {
                        if (err < 0)
                                SetPageError(page);
                        unlock_page(page);
                }
                page_cache_release(page);
                page_cache_release(page);
        }

err_out_free:
        kfree(pages);
        return err;
}

static int pohmelfs_send_readpages(struct pohmelfs_inode *pi, struct page *first, unsigned int num)
{
        struct netfs_trans *t;
        struct netfs_cmd *cmd;
        struct pohmelfs_sb *psb = POHMELFS_SB(pi->vfs_inode.i_sb);
        int err, path_len;
        void *data;

        err = pohmelfs_data_lock(pi, first->index << PAGE_CACHE_SHIFT,
                        num * PAGE_SIZE, POHMELFS_READ_LOCK);
        if (err)
                goto err_out_exit;

        path_len = pohmelfs_path_length(pi);
        if (path_len < 0) {
                err = path_len;
                goto err_out_exit;
        }

        t = netfs_trans_alloc(psb, path_len, NETFS_TRANS_SINGLE_DST, 0);
        if (!t) {
                err = -ENOMEM;
                goto err_out_exit;
        }

        cmd = netfs_trans_current(t);
        data = (void *)(cmd + 1);

        t->complete = pohmelfs_readpages_trans_complete;
        t->private = pi;
        t->page_num = num;
        t->pages = (struct page **)first;

        err = pohmelfs_construct_path_string(pi, data, path_len);
        if (err < 0)
                goto err_out_put;

        path_len = err;

        cmd->cmd = NETFS_READ_PAGES;
        cmd->start = first->index;
        cmd->start <<= PAGE_CACHE_SHIFT;
        cmd->size = (num << 8 | PAGE_CACHE_SHIFT);
        cmd->id = pi->ino;
        cmd->ext = path_len;

        dprintk("%s: t: %p, gen: %u, path: '%s', path_len: %u, "
                        "start: %lu, num: %u.\n",
                        __func__, t, t->gen, (char *)data, path_len,
                        first->index, num);

        netfs_convert_cmd(cmd);
        netfs_trans_update(cmd, t, path_len);

        return netfs_trans_finish(t, psb);

err_out_put:
        netfs_trans_free(t);
err_out_exit:
        pohmelfs_readpages_trans_complete((struct page **)first, num, pi, err);
        return err;
}

#define list_to_page(head) (list_entry((head)->prev, struct page, lru))

static int pohmelfs_readpages(struct file *file, struct address_space *mapping,
                        struct list_head *pages, unsigned nr_pages)
{
        unsigned int page_idx, num = 0;
        struct page *page = NULL, *first = NULL;

        for (page_idx = 0; page_idx < nr_pages; page_idx++) {
                page = list_to_page(pages);

                prefetchw(&page->flags);
                list_del(&page->lru);

                if (!add_to_page_cache_lru(page, mapping,
                                        page->index, GFP_KERNEL)) {

                        if (!num) {
                                num = 1;
                                first = page;
                                continue;
                        }

                        dprintk("%s: added to lru page: %p, page_index: %lu, first_index: %lu.\n",
                                        __func__, page, page->index, first->index);

                        if (unlikely(first->index + num != page->index) || (num > 500)) {
                                pohmelfs_send_readpages(POHMELFS_I(mapping->host),
                                                first, num);
                                first = page;
                                num = 0;
                        }

                        num++;
                }
        }
        pohmelfs_send_readpages(POHMELFS_I(mapping->host), first, num);

        /*
         * This will be sync read, so when last page is processed,
         * all previous are alerady unlocked and ready to be used.
         */
        return 0;
}

/*
 * Small address space operations for POHMELFS.
 */
const struct address_space_operations pohmelfs_aops = {
        .readpage               = pohmelfs_readpage,
        .readpages              = pohmelfs_readpages,
        .writepages             = pohmelfs_writepages,
        .write_begin            = pohmelfs_write_begin,
        .write_end              = pohmelfs_write_end,
        .set_page_dirty         = __set_page_dirty_nobuffers,
};

static void pohmelfs_i_callback(struct rcu_head *head)
{
        struct inode *inode = container_of(head, struct inode, i_rcu);
        INIT_LIST_HEAD(&inode->i_dentry);
        kmem_cache_free(pohmelfs_inode_cache, POHMELFS_I(inode));
}

/*
 * ->detroy_inode() callback. Deletes inode from the caches
 *  and frees private data.
 */
static void pohmelfs_destroy_inode(struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        struct pohmelfs_sb *psb = POHMELFS_SB(sb);
        struct pohmelfs_inode *pi = POHMELFS_I(inode);

        /* pohmelfs_data_unlock(pi, 0, inode->i_size, POHMELFS_READ_LOCK); */

        pohmelfs_inode_del_inode(psb, pi);

        dprintk("%s: pi: %p, inode: %p, ino: %llu.\n",
                __func__, pi, &pi->vfs_inode, pi->ino);
        atomic_long_dec(&psb->total_inodes);
        call_rcu(&inode->i_rcu, pohmelfs_i_callback);
}

/*
 * ->alloc_inode() callback. Allocates inode and initializes private data.
 */
static struct inode *pohmelfs_alloc_inode(struct super_block *sb)
{
        struct pohmelfs_inode *pi;

        pi = kmem_cache_alloc(pohmelfs_inode_cache, GFP_NOIO);
        if (!pi)
                return NULL;

        pi->hash_root = RB_ROOT;
        mutex_init(&pi->offset_lock);

        INIT_LIST_HEAD(&pi->sync_create_list);

        INIT_LIST_HEAD(&pi->inode_entry);

        pi->lock_type = 0;
        pi->state = 0;
        pi->total_len = 0;
        pi->drop_count = 0;

        dprintk("%s: pi: %p, inode: %p.\n", __func__, pi, &pi->vfs_inode);

        atomic_long_inc(&POHMELFS_SB(sb)->total_inodes);

        return &pi->vfs_inode;
}

/*
 * We want fsync() to work on POHMELFS.
 */
static int pohmelfs_fsync(struct file *file, int datasync)
{
        struct inode *inode = file->f_mapping->host;

        return sync_inode_metadata(inode, 1);
}

ssize_t pohmelfs_write(struct file *file, const char __user *buf,
                size_t len, loff_t *ppos)
{
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;
        struct pohmelfs_inode *pi = POHMELFS_I(inode);
        struct iovec iov = { .iov_base = (void __user *)buf, .iov_len = len };
        struct kiocb kiocb;
        ssize_t ret;
        loff_t pos = *ppos;

        init_sync_kiocb(&kiocb, file);
        kiocb.ki_pos = pos;
        kiocb.ki_left = len;

        dprintk("%s: len: %zu, pos: %llu.\n", __func__, len, pos);

        mutex_lock(&inode->i_mutex);
        ret = pohmelfs_data_lock(pi, pos, len, POHMELFS_WRITE_LOCK);
        if (ret)
                goto err_out_unlock;

        ret = __generic_file_aio_write(&kiocb, &iov, 1, &kiocb.ki_pos);
        *ppos = kiocb.ki_pos;

        mutex_unlock(&inode->i_mutex);
        WARN_ON(ret < 0);

        if (ret > 0) {
                ssize_t err;

                err = generic_write_sync(file, pos, ret);
                if (err < 0)
                        ret = err;
                WARN_ON(ret < 0);
        }

        return ret;

err_out_unlock:
        mutex_unlock(&inode->i_mutex);
        return ret;
}

static const struct file_operations pohmelfs_file_ops = {
        .open           = generic_file_open,
        .fsync          = pohmelfs_fsync,

        .llseek         = generic_file_llseek,

        .read           = do_sync_read,
        .aio_read       = generic_file_aio_read,

        .mmap           = generic_file_mmap,

        .splice_read    = generic_file_splice_read,
        .splice_write   = generic_file_splice_write,

        .write          = pohmelfs_write,
        .aio_write      = generic_file_aio_write,
};

const struct inode_operations pohmelfs_symlink_inode_operations = {
        .readlink       = generic_readlink,
        .follow_link    = page_follow_link_light,
        .put_link       = page_put_link,
};

int pohmelfs_setattr_raw(struct inode *inode, struct iattr *attr)
{
        int err;

        err = inode_change_ok(inode, attr);
        if (err) {
                dprintk("%s: ino: %llu, inode changes are not allowed.\n", __func__, POHMELFS_I(inode)->ino);
                goto err_out_exit;
        }

        if ((attr->ia_valid & ATTR_SIZE) &&
            attr->ia_size != i_size_read(inode)) {
                err = vmtruncate(inode, attr->ia_size);
                if (err) {
                        dprintk("%s: ino: %llu, failed to set the attributes.\n", __func__, POHMELFS_I(inode)->ino);
                        goto err_out_exit;
                }
        }

        setattr_copy(inode, attr);
        mark_inode_dirty(inode);

        dprintk("%s: ino: %llu, mode: %o -> %o, uid: %u -> %u, gid: %u -> %u, size: %llu -> %llu.\n",
                        __func__, POHMELFS_I(inode)->ino, inode->i_mode, attr->ia_mode,
                        inode->i_uid, attr->ia_uid, inode->i_gid, attr->ia_gid, inode->i_size, attr->ia_size);

        return 0;

err_out_exit:
        return err;
}

int pohmelfs_setattr(struct dentry *dentry, struct iattr *attr)
{
        struct inode *inode = dentry->d_inode;
        struct pohmelfs_inode *pi = POHMELFS_I(inode);
        int err;

        err = pohmelfs_data_lock(pi, 0, ~0, POHMELFS_WRITE_LOCK);
        if (err)
                goto err_out_exit;

        err = security_inode_setattr(dentry, attr);
        if (err)
                goto err_out_exit;

        err = pohmelfs_setattr_raw(inode, attr);
        if (err)
                goto err_out_exit;

        return 0;

err_out_exit:
        return err;
}

static int pohmelfs_send_xattr_req(struct pohmelfs_inode *pi, u64 id, u64 start,
                const char *name, const void *value, size_t attrsize, int command)
{
        struct pohmelfs_sb *psb = POHMELFS_SB(pi->vfs_inode.i_sb);
        int err, path_len, namelen = strlen(name) + 1; /* 0-byte */
        struct netfs_trans *t;
        struct netfs_cmd *cmd;
        void *data;

        dprintk("%s: id: %llu, start: %llu, name: '%s', attrsize: %zu, cmd: %d.\n",
                        __func__, id, start, name, attrsize, command);

        path_len = pohmelfs_path_length(pi);
        if (path_len < 0) {
                err = path_len;
                goto err_out_exit;
        }

        t = netfs_trans_alloc(psb, namelen + path_len + attrsize, 0, 0);
        if (!t) {
                err = -ENOMEM;
                goto err_out_exit;
        }

        cmd = netfs_trans_current(t);
        data = cmd + 1;

        path_len = pohmelfs_construct_path_string(pi, data, path_len);
        if (path_len < 0) {
                err = path_len;
                goto err_out_put;
        }
        data += path_len;

        /*
         * 'name' is a NUL-terminated string already and
         * 'namelen' includes 0-byte.
         */
        memcpy(data, name, namelen);
        data += namelen;

        memcpy(data, value, attrsize);

        cmd->cmd = command;
        cmd->id = id;
        cmd->start = start;
        cmd->size = attrsize + namelen + path_len;
        cmd->ext = path_len;
        cmd->csize = 0;
        cmd->cpad = 0;

        netfs_convert_cmd(cmd);
        netfs_trans_update(cmd, t, namelen + path_len + attrsize);

        return netfs_trans_finish(t, psb);

err_out_put:
        t->result = err;
        netfs_trans_put(t);
err_out_exit:
        return err;
}

static int pohmelfs_setxattr(struct dentry *dentry, const char *name,
                const void *value, size_t attrsize, int flags)
{
        struct inode *inode = dentry->d_inode;
        struct pohmelfs_inode *pi = POHMELFS_I(inode);
        struct pohmelfs_sb *psb = POHMELFS_SB(inode->i_sb);

        if (!(psb->state_flags & POHMELFS_FLAGS_XATTR))
                return -EOPNOTSUPP;

        return pohmelfs_send_xattr_req(pi, flags, attrsize, name,
                        value, attrsize, NETFS_XATTR_SET);
}

static ssize_t pohmelfs_getxattr(struct dentry *dentry, const char *name,
                void *value, size_t attrsize)
{
        struct inode *inode = dentry->d_inode;
        struct pohmelfs_inode *pi = POHMELFS_I(inode);
        struct pohmelfs_sb *psb = POHMELFS_SB(inode->i_sb);
        struct pohmelfs_mcache *m;
        int err;
        long timeout = psb->mcache_timeout;

        if (!(psb->state_flags & POHMELFS_FLAGS_XATTR))
                return -EOPNOTSUPP;

        m = pohmelfs_mcache_alloc(psb, 0, attrsize, value);
        if (IS_ERR(m))
                return PTR_ERR(m);

        dprintk("%s: ino: %llu, name: '%s', size: %zu.\n",
                        __func__, pi->ino, name, attrsize);

        err = pohmelfs_send_xattr_req(pi, m->gen, attrsize, name, value, 0, NETFS_XATTR_GET);
        if (err)
                goto err_out_put;

        do {
                err = wait_for_completion_timeout(&m->complete, timeout);
                if (err) {
                        err = m->err;
                        break;
                }

                /*
                 * This loop is a bit ugly, since it waits until reference counter
                 * hits 1 and then put object here. Main goal is to prevent race with
                 * network thread, when it can start processing given request, i.e.
                 * increase its reference counter but yet not complete it, while
                 * we will exit from ->getxattr() with timeout, and although request
                 * will not be freed (its reference counter was increased by network
                 * thread), data pointer provided by user may be released, so we will
                 * overwrite already freed area in network thread.
                 *
                 * Now after timeout we remove request from the cache, so it can not be
                 * found by network thread, and wait for its reference counter to hit 1,
                 * i.e. if network thread already started to process this request, we wait
                 * it to finish, and then free object locally. If reference counter is
                 * already 1, i.e. request is not used by anyone else, we can free it without
                 * problem.
                 */
                err = -ETIMEDOUT;
                timeout = HZ;

                pohmelfs_mcache_remove_locked(psb, m);
        } while (atomic_read(&m->refcnt) != 1);

        pohmelfs_mcache_put(psb, m);

        dprintk("%s: ino: %llu, err: %d.\n", __func__, pi->ino, err);

        return err;

err_out_put:
        pohmelfs_mcache_put(psb, m);
        return err;
}

static int pohmelfs_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
{
        struct inode *inode = dentry->d_inode;
#if 0
        struct pohmelfs_inode *pi = POHMELFS_I(inode);
        int err;

        err = pohmelfs_data_lock(pi, 0, ~0, POHMELFS_READ_LOCK);
        if (err)
                return err;
        dprintk("%s: ino: %llu, mode: %o, uid: %u, gid: %u, size: %llu.\n",
                        __func__, pi->ino, inode->i_mode, inode->i_uid,
                        inode->i_gid, inode->i_size);
#endif

        generic_fillattr(inode, stat);
        return 0;
}

const struct inode_operations pohmelfs_file_inode_operations = {
        .setattr        = pohmelfs_setattr,
        .getattr        = pohmelfs_getattr,
        .setxattr       = pohmelfs_setxattr,
        .getxattr       = pohmelfs_getxattr,
};

/*
 * Fill inode data: mode, size, operation callbacks and so on...
 */
void pohmelfs_fill_inode(struct inode *inode, struct netfs_inode_info *info)
{
        inode->i_mode = info->mode;
        inode->i_nlink = info->nlink;
        inode->i_uid = info->uid;
        inode->i_gid = info->gid;
        inode->i_blocks = info->blocks;
        inode->i_rdev = info->rdev;
        inode->i_size = info->size;
        inode->i_version = info->version;
        inode->i_blkbits = ffs(info->blocksize);

        dprintk("%s: inode: %p, num: %lu/%llu inode is regular: %d, dir: %d, link: %d, mode: %o, size: %llu.\n",
                        __func__, inode, inode->i_ino, info->ino,
                        S_ISREG(inode->i_mode), S_ISDIR(inode->i_mode),
                        S_ISLNK(inode->i_mode), inode->i_mode, inode->i_size);

        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME_SEC;

        /*
         * i_mapping is a pointer to i_data during inode initialization.
         */
        inode->i_data.a_ops = &pohmelfs_aops;

        if (S_ISREG(inode->i_mode)) {
                inode->i_fop = &pohmelfs_file_ops;
                inode->i_op = &pohmelfs_file_inode_operations;
        } else if (S_ISDIR(inode->i_mode)) {
                inode->i_fop = &pohmelfs_dir_fops;
                inode->i_op = &pohmelfs_dir_inode_ops;
        } else if (S_ISLNK(inode->i_mode)) {
                inode->i_op = &pohmelfs_symlink_inode_operations;
                inode->i_fop = &pohmelfs_file_ops;
        } else {
                inode->i_fop = &generic_ro_fops;
        }
}

static int pohmelfs_drop_inode(struct inode *inode)
{
        struct pohmelfs_sb *psb = POHMELFS_SB(inode->i_sb);
        struct pohmelfs_inode *pi = POHMELFS_I(inode);

        spin_lock(&psb->ino_lock);
        list_del_init(&pi->inode_entry);
        spin_unlock(&psb->ino_lock);

        return generic_drop_inode(inode);
}

static struct pohmelfs_inode *pohmelfs_get_inode_from_list(struct pohmelfs_sb *psb,
                struct list_head *head, unsigned int *count)
{
        struct pohmelfs_inode *pi = NULL;

        spin_lock(&psb->ino_lock);
        if (!list_empty(head)) {
                pi = list_entry(head->next, struct pohmelfs_inode,
                                        inode_entry);
                list_del_init(&pi->inode_entry);
                *count = pi->drop_count;
                pi->drop_count = 0;
        }
        spin_unlock(&psb->ino_lock);

        return pi;
}

static void pohmelfs_flush_transactions(struct pohmelfs_sb *psb)
{
        struct pohmelfs_config *c;

        mutex_lock(&psb->state_lock);
        list_for_each_entry(c, &psb->state_list, config_entry) {
                pohmelfs_state_flush_transactions(&c->state);
        }
        mutex_unlock(&psb->state_lock);
}

/*
 * ->put_super() callback. Invoked before superblock is destroyed,
 *  so it has to clean all private data.
 */
static void pohmelfs_put_super(struct super_block *sb)
{
        struct pohmelfs_sb *psb = POHMELFS_SB(sb);
        struct pohmelfs_inode *pi;
        unsigned int count = 0;
        unsigned int in_drop_list = 0;
        struct inode *inode, *tmp;

        dprintk("%s.\n", __func__);

        /*
         * Kill pending transactions, which could affect inodes in-flight.
         */
        pohmelfs_flush_transactions(psb);

        while ((pi = pohmelfs_get_inode_from_list(psb, &psb->drop_list, &count))) {
                inode = &pi->vfs_inode;

                dprintk("%s: ino: %llu, pi: %p, inode: %p, count: %u.\n",
                                __func__, pi->ino, pi, inode, count);

                if (atomic_read(&inode->i_count) != count) {
                        printk("%s: ino: %llu, pi: %p, inode: %p, count: %u, i_count: %d.\n",
                                        __func__, pi->ino, pi, inode, count,
                                        atomic_read(&inode->i_count));
                        count = atomic_read(&inode->i_count);
                        in_drop_list++;
                }

                while (count--)
                        iput(&pi->vfs_inode);
        }

        list_for_each_entry_safe(inode, tmp, &sb->s_inodes, i_sb_list) {
                pi = POHMELFS_I(inode);

                dprintk("%s: ino: %llu, pi: %p, inode: %p, i_count: %u.\n",
                                __func__, pi->ino, pi, inode, atomic_read(&inode->i_count));

                /*
                 * These are special inodes, they were created during
                 * directory reading or lookup, and were not bound to dentry,
                 * so they live here with reference counter being 1 and prevent
                 * umount from succeed since it believes that they are busy.
                 */
                count = atomic_read(&inode->i_count);
                if (count) {
                        list_del_init(&inode->i_sb_list);
                        while (count--)
                                iput(&pi->vfs_inode);
                }
        }

        psb->trans_scan_timeout = psb->drop_scan_timeout = 0;
        cancel_delayed_work_sync(&psb->dwork);
        cancel_delayed_work_sync(&psb->drop_dwork);
        flush_scheduled_work();

        dprintk("%s: stopped workqueues.\n", __func__);

        pohmelfs_crypto_exit(psb);
        pohmelfs_state_exit(psb);

        bdi_destroy(&psb->bdi);

        kfree(psb);
        sb->s_fs_info = NULL;
}

static int pohmelfs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
        struct super_block *sb = dentry->d_sb;
        struct pohmelfs_sb *psb = POHMELFS_SB(sb);

        /*
         * There are no filesystem size limits yet.
         */
        memset(buf, 0, sizeof(struct kstatfs));

        buf->f_type = POHMELFS_MAGIC_NUM; /* 'POH.' */
        buf->f_bsize = sb->s_blocksize;
        buf->f_files = psb->ino;
        buf->f_namelen = 255;
        buf->f_files = atomic_long_read(&psb->total_inodes);
        buf->f_bfree = buf->f_bavail = psb->avail_size >> PAGE_SHIFT;
        buf->f_blocks = psb->total_size >> PAGE_SHIFT;

        dprintk("%s: total: %llu, avail: %llu, inodes: %llu, bsize: %lu.\n",
                __func__, psb->total_size, psb->avail_size, buf->f_files, sb->s_blocksize);

        return 0;
}

static int pohmelfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
{
        struct pohmelfs_sb *psb = POHMELFS_SB(vfs->mnt_sb);

        seq_printf(seq, ",idx=%u", psb->idx);
        seq_printf(seq, ",trans_scan_timeout=%u", jiffies_to_msecs(psb->trans_scan_timeout));
        seq_printf(seq, ",drop_scan_timeout=%u", jiffies_to_msecs(psb->drop_scan_timeout));
        seq_printf(seq, ",wait_on_page_timeout=%u", jiffies_to_msecs(psb->wait_on_page_timeout));
        seq_printf(seq, ",trans_retries=%u", psb->trans_retries);
        seq_printf(seq, ",crypto_thread_num=%u", psb->crypto_thread_num);
        seq_printf(seq, ",trans_max_pages=%u", psb->trans_max_pages);
        seq_printf(seq, ",mcache_timeout=%u", jiffies_to_msecs(psb->mcache_timeout));
        if (psb->crypto_fail_unsupported)
                seq_printf(seq, ",crypto_fail_unsupported");

        return 0;
}

enum {
        pohmelfs_opt_idx,
        pohmelfs_opt_crypto_thread_num,
        pohmelfs_opt_trans_max_pages,
        pohmelfs_opt_crypto_fail_unsupported,

        /* Remountable options */
        pohmelfs_opt_trans_scan_timeout,
        pohmelfs_opt_drop_scan_timeout,
        pohmelfs_opt_wait_on_page_timeout,
        pohmelfs_opt_trans_retries,
        pohmelfs_opt_mcache_timeout,
};

static struct match_token pohmelfs_tokens[] = {
        {pohmelfs_opt_idx, "idx=%u"},
        {pohmelfs_opt_crypto_thread_num, "crypto_thread_num=%u"},
        {pohmelfs_opt_trans_max_pages, "trans_max_pages=%u"},
        {pohmelfs_opt_crypto_fail_unsupported, "crypto_fail_unsupported"},
        {pohmelfs_opt_trans_scan_timeout, "trans_scan_timeout=%u"},
        {pohmelfs_opt_drop_scan_timeout, "drop_scan_timeout=%u"},
        {pohmelfs_opt_wait_on_page_timeout, "wait_on_page_timeout=%u"},
        {pohmelfs_opt_trans_retries, "trans_retries=%u"},
        {pohmelfs_opt_mcache_timeout, "mcache_timeout=%u"},
};

static int pohmelfs_parse_options(char *options, struct pohmelfs_sb *psb, int remount)
{
        char *p;
        substring_t args[MAX_OPT_ARGS];
        int option, err;

        if (!options)
                return 0;

        while ((p = strsep(&options, ",")) != NULL) {
                int token;
                if (!*p)
                        continue;

                token = match_token(p, pohmelfs_tokens, args);

                err = match_int(&args[0], &option);
                if (err)
                        return err;

                if (remount && token <= pohmelfs_opt_crypto_fail_unsupported)
                        continue;

                switch (token) {
                case pohmelfs_opt_idx:
                        psb->idx = option;
                        break;
                case pohmelfs_opt_trans_scan_timeout:
                        psb->trans_scan_timeout = msecs_to_jiffies(option);
                        break;
                case pohmelfs_opt_drop_scan_timeout:
                        psb->drop_scan_timeout = msecs_to_jiffies(option);
                        break;
                case pohmelfs_opt_wait_on_page_timeout:
                        psb->wait_on_page_timeout = msecs_to_jiffies(option);
                        break;
                case pohmelfs_opt_mcache_timeout:
                        psb->mcache_timeout = msecs_to_jiffies(option);
                        break;
                case pohmelfs_opt_trans_retries:
                        psb->trans_retries = option;
                        break;
                case pohmelfs_opt_crypto_thread_num:
                        psb->crypto_thread_num = option;
                        break;
                case pohmelfs_opt_trans_max_pages:
                        psb->trans_max_pages = option;
                        break;
                case pohmelfs_opt_crypto_fail_unsupported:
                        psb->crypto_fail_unsupported = 1;
                        break;
                default:
                        return -EINVAL;
                }
        }

        return 0;
}

static int pohmelfs_remount(struct super_block *sb, int *flags, char *data)
{
        int err;
        struct pohmelfs_sb *psb = POHMELFS_SB(sb);
        unsigned long old_sb_flags = sb->s_flags;

        err = pohmelfs_parse_options(data, psb, 1);
        if (err)
                goto err_out_restore;

        if (!(*flags & MS_RDONLY))
                sb->s_flags &= ~MS_RDONLY;
        return 0;

err_out_restore:
        sb->s_flags = old_sb_flags;
        return err;
}

static void pohmelfs_flush_inode(struct pohmelfs_inode *pi, unsigned int count)
{
        struct inode *inode = &pi->vfs_inode;

        dprintk("%s: %p: ino: %llu, owned: %d.\n",
                __func__, inode, pi->ino, test_bit(NETFS_INODE_OWNED, &pi->state));

        mutex_lock(&inode->i_mutex);
        if (test_and_clear_bit(NETFS_INODE_OWNED, &pi->state)) {
                filemap_fdatawrite(inode->i_mapping);
                inode->i_sb->s_op->write_inode(inode, 0);
        }

#ifdef POHMELFS_TRUNCATE_ON_INODE_FLUSH
        truncate_inode_pages(inode->i_mapping, 0);
#endif

        pohmelfs_data_unlock(pi, 0, ~0, POHMELFS_WRITE_LOCK);
        mutex_unlock(&inode->i_mutex);
}

static void pohmelfs_put_inode_count(struct pohmelfs_inode *pi, unsigned int count)
{
        dprintk("%s: ino: %llu, pi: %p, inode: %p, count: %u.\n",
                        __func__, pi->ino, pi, &pi->vfs_inode, count);

        if (test_and_clear_bit(NETFS_INODE_NEED_FLUSH, &pi->state))
                pohmelfs_flush_inode(pi, count);

        while (count--)
                iput(&pi->vfs_inode);
}

static void pohmelfs_drop_scan(struct work_struct *work)
{
        struct pohmelfs_sb *psb =
                container_of(work, struct pohmelfs_sb, drop_dwork.work);
        struct pohmelfs_inode *pi;
        unsigned int count = 0;

        while ((pi = pohmelfs_get_inode_from_list(psb, &psb->drop_list, &count)))
                pohmelfs_put_inode_count(pi, count);

        pohmelfs_check_states(psb);

        if (psb->drop_scan_timeout)
                schedule_delayed_work(&psb->drop_dwork, psb->drop_scan_timeout);
}

/*
 * Run through all transactions starting from the oldest,
 * drop transaction from current state and try to send it
 * to all remote nodes, which are currently installed.
 */
static void pohmelfs_trans_scan_state(struct netfs_state *st)
{
        struct rb_node *rb_node;
        struct netfs_trans_dst *dst;
        struct pohmelfs_sb *psb = st->psb;
        unsigned int timeout = psb->trans_scan_timeout;
        struct netfs_trans *t;
        int err;

        mutex_lock(&st->trans_lock);
        for (rb_node = rb_first(&st->trans_root); rb_node; ) {
                dst = rb_entry(rb_node, struct netfs_trans_dst, state_entry);
                t = dst->trans;

                if (timeout && time_after(dst->send_time + timeout, jiffies)
                                && dst->retries == 0)
                        break;

                dprintk("%s: t: %p, gen: %u, st: %p, retries: %u, max: %u.\n",
                        __func__, t, t->gen, st, dst->retries, psb->trans_retries);
                netfs_trans_get(t);

                rb_node = rb_next(rb_node);

                err = -ETIMEDOUT;
                if (timeout && (++dst->retries < psb->trans_retries))
                        err = netfs_trans_resend(t, psb);

                if (err || (t->flags & NETFS_TRANS_SINGLE_DST)) {
                        if (netfs_trans_remove_nolock(dst, st))
                                netfs_trans_drop_dst_nostate(dst);
                }

                t->result = err;
                netfs_trans_put(t);
        }
        mutex_unlock(&st->trans_lock);
}

/*
 * Walk through all installed network states and resend all
 * transactions, which are old enough.
 */
static void pohmelfs_trans_scan(struct work_struct *work)
{
        struct pohmelfs_sb *psb =
                container_of(work, struct pohmelfs_sb, dwork.work);
        struct netfs_state *st;
        struct pohmelfs_config *c;

        mutex_lock(&psb->state_lock);
        list_for_each_entry(c, &psb->state_list, config_entry) {
                st = &c->state;

                pohmelfs_trans_scan_state(st);
        }
        mutex_unlock(&psb->state_lock);

        /*
         * If no timeout specified then system is in the middle of umount process,
         * so no need to reschedule scanning process again.
         */
        if (psb->trans_scan_timeout)
                schedule_delayed_work(&psb->dwork, psb->trans_scan_timeout);
}

int pohmelfs_meta_command_data(struct pohmelfs_inode *pi, u64 id, unsigned int cmd_op, char *addon,
                unsigned int flags, netfs_trans_complete_t complete, void *priv, u64 start)
{
        struct inode *inode = &pi->vfs_inode;
        struct pohmelfs_sb *psb = POHMELFS_SB(inode->i_sb);
        int err = 0, sz;
        struct netfs_trans *t;
        int path_len, addon_len = 0;
        void *data;
        struct netfs_inode_info *info;
        struct netfs_cmd *cmd;

        dprintk("%s: ino: %llu, cmd: %u, addon: %p.\n", __func__, pi->ino, cmd_op, addon);

        path_len = pohmelfs_path_length(pi);
        if (path_len < 0) {
                err = path_len;
                goto err_out_exit;
        }

        if (addon)
                addon_len = strlen(addon) + 1; /* 0-byte */
        sz = addon_len;

        if (cmd_op == NETFS_INODE_INFO)
                sz += sizeof(struct netfs_inode_info);

        t = netfs_trans_alloc(psb, sz + path_len, flags, 0);
        if (!t) {
                err = -ENOMEM;
                goto err_out_exit;
        }
        t->complete = complete;
        t->private = priv;

        cmd = netfs_trans_current(t);
        data = (void *)(cmd + 1);

        if (cmd_op == NETFS_INODE_INFO) {
                info = (struct netfs_inode_info *)(cmd + 1);
                data = (void *)(info + 1);

                /*
                 * We are under i_mutex, can read and change whatever we want...
                 */
                info->mode = inode->i_mode;
                info->nlink = inode->i_nlink;
                info->uid = inode->i_uid;
                info->gid = inode->i_gid;
                info->blocks = inode->i_blocks;
                info->rdev = inode->i_rdev;
                info->size = inode->i_size;
                info->version = inode->i_version;

                netfs_convert_inode_info(info);
        }

        path_len = pohmelfs_construct_path_string(pi, data, path_len);
        if (path_len < 0)
                goto err_out_free;

        dprintk("%s: path_len: %d.\n", __func__, path_len);

        if (addon) {
                path_len--; /* Do not place null-byte before the addon */
                path_len += sprintf(data + path_len, "/%s", addon) + 1; /* 0 - byte */
        }

        sz += path_len;

        cmd->cmd = cmd_op;
        cmd->ext = path_len;
        cmd->size = sz;
        cmd->id = id;
        cmd->start = start;

        netfs_convert_cmd(cmd);
        netfs_trans_update(cmd, t, sz);

        /*
         * Note, that it is possible to leak error here: transaction callback will not
         * be invoked for allocation path failure.
         */
        return netfs_trans_finish(t, psb);

err_out_free:
        netfs_trans_free(t);
err_out_exit:
        if (complete)
                complete(NULL, 0, priv, err);
        return err;
}

int pohmelfs_meta_command(struct pohmelfs_inode *pi, unsigned int cmd_op, unsigned int flags,
                netfs_trans_complete_t complete, void *priv, u64 start)
{
        return pohmelfs_meta_command_data(pi, pi->ino, cmd_op, NULL, flags, complete, priv, start);
}

/*
 * Send request and wait for POHMELFS root capabilities response,
 * which will update server's informaion about size of the export,
 * permissions, number of objects, available size and so on.
 */
static int pohmelfs_root_handshake(struct pohmelfs_sb *psb)
{
        struct netfs_trans *t;
        struct netfs_cmd *cmd;
        int err = -ENOMEM;

        t = netfs_trans_alloc(psb, 0, 0, 0);
        if (!t)
                goto err_out_exit;

        cmd = netfs_trans_current(t);

        cmd->cmd = NETFS_CAPABILITIES;
        cmd->id = POHMELFS_ROOT_CAPABILITIES;
        cmd->size = 0;
        cmd->start = 0;
        cmd->ext = 0;
        cmd->csize = 0;

        netfs_convert_cmd(cmd);
        netfs_trans_update(cmd, t, 0);

        err = netfs_trans_finish(t, psb);
        if (err)
                goto err_out_exit;

        psb->flags = ~0;
        err = wait_event_interruptible_timeout(psb->wait,
                        (psb->flags != ~0),
                        psb->wait_on_page_timeout);
        if (!err)
                err = -ETIMEDOUT;
        else if (err > 0)
                err = -psb->flags;

        if (err)
                goto err_out_exit;

        return 0;

err_out_exit:
        return err;
}

static int pohmelfs_show_stats(struct seq_file *m, struct vfsmount *mnt)
{
        struct netfs_state *st;
        struct pohmelfs_ctl *ctl;
        struct pohmelfs_sb *psb = POHMELFS_SB(mnt->mnt_sb);
        struct pohmelfs_config *c;

        mutex_lock(&psb->state_lock);

        seq_printf(m, "\nidx addr(:port) socket_type protocol active priority permissions\n");

        list_for_each_entry(c, &psb->state_list, config_entry) {
                st = &c->state;
                ctl = &st->ctl;

                seq_printf(m, "%u ", ctl->idx);
                if (ctl->addr.sa_family == AF_INET) {
                        struct sockaddr_in *sin = (struct sockaddr_in *)&st->ctl.addr;
                        seq_printf(m, "%pI4:%u", &sin->sin_addr.s_addr, ntohs(sin->sin_port));
                } else if (ctl->addr.sa_family == AF_INET6) {
                        struct sockaddr_in6 *sin = (struct sockaddr_in6 *)&st->ctl.addr;
                        seq_printf(m, "%pi6:%u", &sin->sin6_addr, ntohs(sin->sin6_port));
                } else {
                        unsigned int i;
                        for (i = 0; i < ctl->addrlen; ++i)
                                seq_printf(m, "%02x.", ctl->addr.addr[i]);
                }

                seq_printf(m, " %u %u %d %u %x\n",
                                ctl->type, ctl->proto,
                                st->socket != NULL,
                                ctl->prio, ctl->perm);
        }
        mutex_unlock(&psb->state_lock);

        return 0;
}

static const struct super_operations pohmelfs_sb_ops = {
        .alloc_inode    = pohmelfs_alloc_inode,
        .destroy_inode  = pohmelfs_destroy_inode,
        .drop_inode     = pohmelfs_drop_inode,
        .write_inode    = pohmelfs_write_inode,
        .put_super      = pohmelfs_put_super,
        .remount_fs     = pohmelfs_remount,
        .statfs         = pohmelfs_statfs,
        .show_options   = pohmelfs_show_options,
        .show_stats     = pohmelfs_show_stats,
};

/*
 * Allocate private superblock and create root dir.
 */
static int pohmelfs_fill_super(struct super_block *sb, void *data, int silent)
{
        struct pohmelfs_sb *psb;
        int err = -ENOMEM;
        struct inode *root;
        struct pohmelfs_inode *npi;
        struct qstr str;

        psb = kzalloc(sizeof(struct pohmelfs_sb), GFP_KERNEL);
        if (!psb)
                goto err_out_exit;

        err = bdi_init(&psb->bdi);
        if (err)
                goto err_out_free_sb;

        err = bdi_register(&psb->bdi, NULL, "pfs-%d", atomic_inc_return(&psb_bdi_num));
        if (err) {
                bdi_destroy(&psb->bdi);
                goto err_out_free_sb;
        }

        sb->s_fs_info = psb;
        sb->s_op = &pohmelfs_sb_ops;
        sb->s_magic = POHMELFS_MAGIC_NUM;
        sb->s_maxbytes = MAX_LFS_FILESIZE;
        sb->s_blocksize = PAGE_SIZE;
        sb->s_bdi = &psb->bdi;

        psb->sb = sb;

        psb->ino = 2;
        psb->idx = 0;
        psb->active_state = NULL;
        psb->trans_retries = 5;
        psb->trans_data_size = PAGE_SIZE;
        psb->drop_scan_timeout = msecs_to_jiffies(1000);
        psb->trans_scan_timeout = msecs_to_jiffies(5000);
        psb->wait_on_page_timeout = msecs_to_jiffies(5000);
        init_waitqueue_head(&psb->wait);

        spin_lock_init(&psb->ino_lock);

        INIT_LIST_HEAD(&psb->drop_list);

        mutex_init(&psb->mcache_lock);
        psb->mcache_root = RB_ROOT;
        psb->mcache_timeout = msecs_to_jiffies(5000);
        atomic_long_set(&psb->mcache_gen, 0);

        psb->trans_max_pages = 100;

        psb->crypto_align_size = 16;
        psb->crypto_attached_size = 0;
        psb->hash_strlen = 0;
        psb->cipher_strlen = 0;
        psb->perform_crypto = 0;
        psb->crypto_thread_num = 2;
        psb->crypto_fail_unsupported = 0;
        mutex_init(&psb->crypto_thread_lock);
        INIT_LIST_HEAD(&psb->crypto_ready_list);
        INIT_LIST_HEAD(&psb->crypto_active_list);

        atomic_set(&psb->trans_gen, 1);
        atomic_long_set(&psb->total_inodes, 0);

        mutex_init(&psb->state_lock);
        INIT_LIST_HEAD(&psb->state_list);

        err = pohmelfs_parse_options((char *) data, psb, 0);
        if (err)
                goto err_out_free_bdi;

        err = pohmelfs_copy_crypto(psb);
        if (err)
                goto err_out_free_bdi;

        err = pohmelfs_state_init(psb);
        if (err)
                goto err_out_free_strings;

        err = pohmelfs_crypto_init(psb);
        if (err)
                goto err_out_state_exit;

        err = pohmelfs_root_handshake(psb);
        if (err)
                goto err_out_crypto_exit;

        str.name = "/";
        str.hash = jhash("/", 1, 0);
        str.len = 1;

        npi = pohmelfs_create_entry_local(psb, NULL, &str, 0, 0755|S_IFDIR);
        if (IS_ERR(npi)) {
                err = PTR_ERR(npi);
                goto err_out_crypto_exit;
        }
        set_bit(NETFS_INODE_REMOTE_SYNCED, &npi->state);
        clear_bit(NETFS_INODE_OWNED, &npi->state);

        root = &npi->vfs_inode;

        sb->s_root = d_alloc_root(root);
        if (!sb->s_root)
                goto err_out_put_root;

        INIT_DELAYED_WORK(&psb->drop_dwork, pohmelfs_drop_scan);
        schedule_delayed_work(&psb->drop_dwork, psb->drop_scan_timeout);

        INIT_DELAYED_WORK(&psb->dwork, pohmelfs_trans_scan);
        schedule_delayed_work(&psb->dwork, psb->trans_scan_timeout);

        return 0;

err_out_put_root:
        iput(root);
err_out_crypto_exit:
        pohmelfs_crypto_exit(psb);
err_out_state_exit:
        pohmelfs_state_exit(psb);
err_out_free_strings:
        kfree(psb->cipher_string);
        kfree(psb->hash_string);
err_out_free_bdi:
        bdi_destroy(&psb->bdi);
err_out_free_sb:
        kfree(psb);
err_out_exit:

        dprintk("%s: err: %d.\n", __func__, err);
        return err;
}

/*
 * Some VFS magic here...
 */
static struct dentry *pohmelfs_mount(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *data)
{
        return mount_nodev(fs_type, flags, data, pohmelfs_fill_super);
}

/*
 * We need this to sync all inodes earlier, since when writeback
 * is invoked from the umount/mntput path dcache is already shrunk,
 * see generic_shutdown_super(), and no inodes can access the path.
 */
static void pohmelfs_kill_super(struct super_block *sb)
{
        sync_inodes_sb(sb);
        kill_anon_super(sb);
}

static struct file_system_type pohmel_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "pohmel",
        .mount          = pohmelfs_mount,
        .kill_sb        = pohmelfs_kill_super,
};

/*
 * Cache and module initializations and freeing routings.
 */
static void pohmelfs_init_once(void *data)
{
        struct pohmelfs_inode *pi = data;

        inode_init_once(&pi->vfs_inode);
}

static int __init pohmelfs_init_inodecache(void)
{
        pohmelfs_inode_cache = kmem_cache_create("pohmelfs_inode_cache",
                                sizeof(struct pohmelfs_inode),
                                0, (SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD),
                                pohmelfs_init_once);
        if (!pohmelfs_inode_cache)
                return -ENOMEM;

        return 0;
}

static void pohmelfs_destroy_inodecache(void)
{
        kmem_cache_destroy(pohmelfs_inode_cache);
}

static int __init init_pohmel_fs(void)
{
        int err;

        err = pohmelfs_config_init();
        if (err)
                goto err_out_exit;

        err = pohmelfs_init_inodecache();
        if (err)
                goto err_out_config_exit;

        err = pohmelfs_mcache_init();
        if (err)
                goto err_out_destroy;

        err = netfs_trans_init();
        if (err)
                goto err_out_mcache_exit;

        err = register_filesystem(&pohmel_fs_type);
        if (err)
                goto err_out_trans;

        return 0;

err_out_trans:
        netfs_trans_exit();
err_out_mcache_exit:
        pohmelfs_mcache_exit();
err_out_destroy:
        pohmelfs_destroy_inodecache();
err_out_config_exit:
        pohmelfs_config_exit();
err_out_exit:
        return err;
}

static void __exit exit_pohmel_fs(void)
{
        unregister_filesystem(&pohmel_fs_type);
        pohmelfs_destroy_inodecache();
        pohmelfs_mcache_exit();
        pohmelfs_config_exit();
        netfs_trans_exit();
}

module_init(init_pohmel_fs);
module_exit(exit_pohmel_fs);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
MODULE_DESCRIPTION("Pohmel filesystem");