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    Subject[4/4] DST: Algorithms used in distributed storage.
    Date
    From

    Algorithms used in distributed storage.
    Mirror and linear mapping code.

    Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>


    diff --git a/drivers/block/dst/alg_linear.c b/drivers/block/dst/alg_linear.c
    new file mode 100644
    index 0000000..836764d
    --- /dev/null
    +++ b/drivers/block/dst/alg_linear.c
    @@ -0,0 +1,114 @@
    +/*
    + * 2007+ Copyright (c) Evgeniy Polyakov <johnpol@2ka.mipt.ru>
    + * 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/kernel.h>
    +#include <linux/init.h>
    +#include <linux/dst.h>
    +
    +static struct dst_alg *alg_linear;
    +
    +/*
    + * This callback is invoked when node is removed from storage.
    + */
    +static void dst_linear_del_node(struct dst_node *n)
    +{
    +}
    +
    +/*
    + * This callback is invoked when node is added to storage.
    + */
    +static int dst_linear_add_node(struct dst_node *n)
    +{
    + struct dst_storage *st = n->st;
    + struct block_device *bdev;
    +
    + dprintk("%s: disk_size: %llu, node_size: %llu.\n",
    + __func__, st->disk_size, n->size);
    +
    + mutex_lock(&st->tree_lock);
    + n->start = st->disk_size;
    + st->disk_size += n->size;
    + set_capacity(st->disk, st->disk_size);
    +
    + bdev = bdget_disk(st->disk, 0);
    + if (bdev) {
    + mutex_lock(&bdev->bd_inode->i_mutex);
    + i_size_write(bdev->bd_inode, to_bytes(st->disk_size));
    + mutex_unlock(&bdev->bd_inode->i_mutex);
    + bdput(bdev);
    + }
    + mutex_unlock(&st->tree_lock);
    +
    + return 0;
    +}
    +
    +static int dst_linear_remap(struct dst_request *req)
    +{
    + int err;
    +
    + if (req->node->bdev) {
    + generic_make_request(req->bio);
    + return 0;
    + }
    +
    + err = kst_check_permissions(req->state, req->bio);
    + if (err)
    + return err;
    +
    + return req->state->ops->push(req);
    +}
    +
    +/*
    + * Failover callback - it is invoked each time error happens during
    + * request processing.
    + */
    +static int dst_linear_error(struct kst_state *st, int err)
    +{
    + if (err)
    + set_bit(DST_NODE_FROZEN, &st->node->flags);
    + else
    + clear_bit(DST_NODE_FROZEN, &st->node->flags);
    + return 0;
    +}
    +
    +static struct dst_alg_ops alg_linear_ops = {
    + .remap = dst_linear_remap,
    + .add_node = dst_linear_add_node,
    + .del_node = dst_linear_del_node,
    + .error = dst_linear_error,
    + .owner = THIS_MODULE,
    +};
    +
    +static int __devinit alg_linear_init(void)
    +{
    + alg_linear = dst_alloc_alg("alg_linear", &alg_linear_ops);
    + if (!alg_linear)
    + return -ENOMEM;
    +
    + return 0;
    +}
    +
    +static void __devexit alg_linear_exit(void)
    +{
    + dst_remove_alg(alg_linear);
    +}
    +
    +module_init(alg_linear_init);
    +module_exit(alg_linear_exit);
    +
    +MODULE_LICENSE("GPL");
    +MODULE_AUTHOR("Evgeniy Polyakov <johnpol@2ka.mipt.ru>");
    +MODULE_DESCRIPTION("Linear distributed algorithm.");
    diff --git a/drivers/block/dst/alg_mirror.c b/drivers/block/dst/alg_mirror.c
    new file mode 100644
    index 0000000..c10d582
    --- /dev/null
    +++ b/drivers/block/dst/alg_mirror.c
    @@ -0,0 +1,1536 @@
    +/*
    + * 2007+ Copyright (c) Evgeniy Polyakov <johnpol@2ka.mipt.ru>
    + * 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/kernel.h>
    +#include <linux/init.h>
    +#include <linux/poll.h>
    +#include <linux/dst.h>
    +#include <linux/vmstat.h>
    +
    +struct dst_write_entry
    +{
    + int error;
    + u32 size;
    + u64 start;
    +};
    +#define DST_LOG_ENTRIES_PER_PAGE (PAGE_SIZE/sizeof(struct dst_write_entry))
    +
    +struct dst_mirror_node_data
    +{
    + u64 age;
    + u64 num, write_idx, resync_idx;
    +};
    +
    +struct dst_mirror_log
    +{
    + unsigned int nr_pages;
    + struct dst_write_entry **entries;
    +};
    +
    +struct dst_mirror_priv
    +{
    + u64 resync_start, resync_size;
    + atomic_t resync_num;
    + struct completion resync_complete;
    + struct delayed_work resync_work;
    + unsigned int resync_timeout;
    +
    + u64 last_start;
    +
    + spinlock_t resync_wait_lock;
    + struct list_head resync_wait_list;
    + int resync_wait_num;
    + int full_resync;
    +
    + spinlock_t backlog_lock;
    + struct list_head backlog_list;
    +
    + struct dst_node *node;
    +
    + u64 old_age, ndp_sector;
    + struct dst_mirror_node_data data;
    +
    + spinlock_t log_lock;
    + struct dst_mirror_log log;
    +};
    +
    +struct dst_mirror_sync_container
    +{
    + struct list_head sync_entry;
    + u64 start, size;
    + struct dst_node *node;
    + struct bio *bio;
    +};
    +
    +static struct dst_alg *alg_mirror;
    +static struct bio_set *dst_mirror_bio_set;
    +
    +static int dst_mirror_resync(struct dst_node *n, int ndp);
    +
    +static int dst_mirror_mark_notsync(struct dst_node *n)
    +{
    + if (!test_and_set_bit(DST_NODE_NOTSYNC, &n->flags)) {
    + struct dst_mirror_priv *priv = n->priv;
    + printk(KERN_NOTICE "%s: not synced node n: %p.\n", __func__, n);
    +
    + priv->data.resync_idx = priv->data.write_idx;
    + return 1;
    + }
    +
    + return 0;
    +}
    +
    +static void dst_mirror_mark_node_sync(struct dst_node *n)
    +{
    + struct dst_mirror_priv *priv = n->priv;
    +
    + if (test_and_clear_bit(DST_NODE_NOTSYNC, &n->flags))
    + printk(KERN_NOTICE "%s: node: %p, %llu:%llu synchronization "
    + "has been completed.\n",
    + __func__, n, n->start, n->size);
    +
    + priv->full_resync = 0;
    + complete(&priv->resync_complete);
    +}
    +
    +static ssize_t dst_mirror_mark_dirty(struct device *dev, struct device_attribute *attr,
    + const char *buf, size_t count)
    +{
    + struct dst_node *n = container_of(dev, struct dst_node, device);
    +
    + dst_mirror_mark_notsync(n);
    + return count;
    +}
    +
    +static ssize_t dst_mirror_mark_clean(struct device *dev, struct device_attribute *attr,
    + const char *buf, size_t count)
    +{
    + struct dst_node *n = container_of(dev, struct dst_node, device);
    +
    + dst_mirror_mark_node_sync(n);
    + return count;
    +}
    +
    +static ssize_t dst_mirror_show_state(struct device *dev, struct device_attribute *attr,
    + char *buf)
    +{
    + struct dst_node *n = container_of(dev, struct dst_node, device);
    +
    + return sprintf(buf, "%s\n", test_bit(DST_NODE_NOTSYNC, &n->flags) ? "notsync" : "sync");
    +}
    +
    +static ssize_t dst_mirror_show_resync_timeout(struct device *dev, struct device_attribute *attr,
    + char *buf)
    +{
    + struct dst_node *n = container_of(dev, struct dst_node, device);
    + struct dst_mirror_priv *priv = n->priv;
    +
    + return sprintf(buf, "%u\n", priv->resync_timeout);
    +}
    +
    +static ssize_t dst_mirror_show_resync_size(struct device *dev, struct device_attribute *attr,
    + char *buf)
    +{
    + struct dst_node *n = container_of(dev, struct dst_node, device);
    + struct dst_mirror_priv *priv = n->priv;
    +
    + return sprintf(buf, "%llu\n", priv->resync_size);
    +}
    +
    +static ssize_t dst_mirror_set_resync_size(struct device *dev, struct device_attribute *attr,
    + const char *buf, size_t count)
    +{
    + struct dst_node *n = container_of(dev, struct dst_node, device);
    + struct dst_mirror_priv *priv = n->priv;
    + unsigned long size;
    +
    + size = simple_strtoul(buf, NULL, 0);
    +
    + if (size > n->st->disk_size)
    + return -E2BIG;
    +
    + priv->resync_size = size;
    +
    + return count;
    +}
    +
    +static ssize_t dst_mirror_show_log_num(struct device *dev, struct device_attribute *attr,
    + char *buf)
    +{
    + struct dst_node *n = container_of(dev, struct dst_node, device);
    + struct dst_mirror_priv *priv = n->priv;
    +
    + return sprintf(buf, "%llu\n", priv->data.num);
    +}
    +
    +static ssize_t dst_mirror_set_resync_timeout(struct device *dev, struct device_attribute *attr,
    + const char *buf, size_t count)
    +{
    + struct dst_node *n = container_of(dev, struct dst_node, device);
    + struct dst_mirror_priv *priv = n->priv;
    + unsigned long tm;
    +
    + tm = simple_strtoul(buf, NULL, 0);
    +
    + if (tm < 100 || tm > 30000)
    + return -EINVAL;
    +
    + priv->resync_timeout = (unsigned int)tm;
    +
    + return count;
    +}
    +
    +static struct device_attribute dst_mirror_attrs[] = {
    + __ATTR(dirty, S_IWUSR, NULL, dst_mirror_mark_dirty),
    + __ATTR(clean, S_IWUSR, NULL, dst_mirror_mark_clean),
    + __ATTR(resync_size, S_IWUSR | S_IRUGO, dst_mirror_show_resync_size,
    + dst_mirror_set_resync_size),
    + __ATTR(resync_timeout, S_IWUSR | S_IRUGO, dst_mirror_show_resync_timeout,
    + dst_mirror_set_resync_timeout),
    + __ATTR(state, S_IRUSR, dst_mirror_show_state, NULL),
    + __ATTR(log_num, S_IRUSR, dst_mirror_show_log_num, NULL),
    +};
    +
    +static void dst_mirror_handle_priv(struct dst_node *n)
    +{
    + if (n->priv) {
    + int err, i;
    +
    + for (i=0; i<ARRAY_SIZE(dst_mirror_attrs); ++i)
    + err = device_create_file(&n->device,
    + &dst_mirror_attrs[i]);
    + }
    +}
    +
    +static void dst_mirror_destructor(struct bio *bio)
    +{
    + dprintk("%s: bio: %p.\n", __func__, bio);
    + bio_free(bio, dst_mirror_bio_set);
    +}
    +
    +struct dst_mirror_ndp
    +{
    + int err;
    + struct page *page;
    + struct completion complete;
    +};
    +
    +static void dst_mirror_ndb_complete(struct dst_mirror_ndp *cmp, int err)
    +{
    + cmp->err = err;
    + dprintk("%s: completing request: cmp: %p, err: %d.\n",
    + __func__, cmp, err);
    + complete(&cmp->complete);
    +}
    +
    +static void dst_mirror_ndp_bio_endio(struct dst_request *req, int err)
    +{
    + struct dst_mirror_ndp *cmp = req->bio->bi_private;
    +
    + dst_mirror_ndb_complete(cmp, err);
    +}
    +
    +static int dst_mirror_ndp_end_io(struct bio *bio, unsigned int size, int err)
    +{
    + struct dst_mirror_ndp *cmp = bio->bi_private;
    +
    + if (bio->bi_size)
    + return 0;
    +
    + dst_mirror_ndb_complete(cmp, err);
    + return 0;
    +}
    +
    +/*
    + * This function reads or writes node's private data from underlying media.
    + */
    +static int dst_mirror_process_node_data(struct dst_node *n,
    + struct dst_mirror_node_data *ndata, int op)
    +{
    + struct bio *bio;
    + int err = -ENOMEM;
    + struct dst_mirror_ndp *cmp;
    + struct dst_mirror_priv *priv = n->priv;
    + void *addr;
    +
    + cmp = kzalloc(sizeof(struct dst_mirror_ndp), GFP_KERNEL);
    + if (!cmp)
    + goto err_out_exit;
    +
    + cmp->page = alloc_page(GFP_NOIO);
    + if (!cmp->page)
    + goto err_out_free_cmp;
    +
    + addr = kmap(cmp->page);
    +
    + init_completion(&cmp->complete);
    +
    + if (op == WRITE)
    + memcpy(addr, ndata, sizeof(struct dst_mirror_node_data));
    +
    + bio = bio_alloc_bioset(GFP_NOIO, 1, dst_mirror_bio_set);
    + if (!bio)
    + goto err_out_free_page;
    +
    + bio->bi_rw = op;
    + bio->bi_private = cmp;
    + bio->bi_sector = priv->ndp_sector;
    + bio->bi_bdev = n->bdev;
    + bio->bi_destructor = dst_mirror_destructor;
    + bio->bi_end_io = dst_mirror_ndp_end_io;
    +
    + err = bio_add_pc_page(n->st->queue, bio, cmp->page, 512, 0);
    + if (err <= 0)
    + goto err_out_free_bio;
    +
    + if (n->bdev) {
    + generic_make_request(bio);
    + } else {
    + struct dst_request req;
    +
    + memset(&req, 0, sizeof(struct dst_request));
    + dst_fill_request(&req, bio, bio->bi_sector, n,
    + &dst_mirror_ndp_bio_endio);
    +
    + err = req.state->ops->push(&req);
    + if (err)
    + req.bio_endio(&req, err);
    + }
    +
    + dprintk("%s: waiting for completion: bio: %p, cmp: %p.\n",
    + __func__, bio, cmp);
    +
    + wait_for_completion(&cmp->complete);
    +
    + err = cmp->err;
    + if (!err && (op != WRITE))
    + memcpy(ndata, addr, sizeof(struct dst_mirror_node_data));
    +
    + kunmap(cmp->page);
    +
    + dprintk("%s: freeing bio: %p, err: %d.\n", __func__, bio, err);
    +
    +err_out_free_bio:
    + bio_put(bio);
    +err_out_free_page:
    + kunmap(cmp->page);
    + __free_page(cmp->page);
    +err_out_free_cmp:
    + kfree(cmp);
    +err_out_exit:
    + return err;
    +}
    +
    +/*
    + * This function reads node's private data from underlying media.
    + */
    +static int dst_mirror_read_node_data(struct dst_node *n,
    + struct dst_mirror_node_data *ndata)
    +{
    + return dst_mirror_process_node_data(n, ndata, READ);
    +}
    +
    +/*
    + * This function writes node's private data from underlying media.
    + */
    +static int dst_mirror_write_node_data(struct dst_node *n,
    + struct dst_mirror_node_data *ndata)
    +{
    + dprintk("%s: writing new age: %llx, node: %p %llu-%llu.\n",
    + __func__, ndata->age, n, n->start, n->size);
    + return dst_mirror_process_node_data(n, ndata, WRITE);
    +}
    +
    +static int dst_mirror_process_log_on_disk(struct dst_node *n, int op)
    +{
    + struct dst_mirror_priv *priv = n->priv;
    + struct dst_mirror_log *log = &priv->log;
    + int err = -ENOMEM;
    + unsigned int i;
    + struct bio *bio;
    + struct dst_mirror_ndp *cmp;
    +
    + cmp = kzalloc(sizeof(struct dst_mirror_ndp), GFP_KERNEL);
    + if (!cmp)
    + goto err_out_exit;
    +
    + bio = bio_alloc_bioset(GFP_NOIO, 1, dst_mirror_bio_set);
    + if (!bio)
    + goto err_out_free_cmp;
    +
    + bio->bi_rw = op;
    + bio->bi_private = cmp;
    + bio->bi_bdev = n->bdev;
    + bio->bi_destructor = dst_mirror_destructor;
    + bio->bi_end_io = dst_mirror_ndp_end_io;
    +
    + for (i=0; i<log->nr_pages; ++i) {
    + bio->bi_sector = n->size + to_sector(i*PAGE_SIZE);
    +
    + err = bio_add_pc_page(n->st->queue, bio,
    + virt_to_page(log->entries[i]), PAGE_SIZE,
    + offset_in_page(log->entries[i]));
    + if (err <= 0)
    + goto err_out_free_bio;
    +
    + init_completion(&cmp->complete);
    +
    + if (n->bdev) {
    + generic_make_request(bio);
    + } else {
    + struct dst_request req;
    +
    + memset(&req, 0, sizeof(struct dst_request));
    + dst_fill_request(&req, bio, bio->bi_sector, n,
    + &dst_mirror_ndp_bio_endio);
    +
    + err = req.state->ops->push(&req);
    + if (err)
    + req.bio_endio(&req, err);
    + }
    +
    + dprintk("%s: waiting for completion: bio: %p, cmp: %p.\n",
    + __func__, bio, cmp);
    +
    + wait_for_completion(&cmp->complete);
    + if (cmp->err) {
    + err = cmp->err;
    + goto err_out_free_bio;
    + }
    + }
    +
    + err = dst_mirror_write_node_data(n, &priv->data);
    + if (err)
    + goto err_out_free_cmp;
    +
    +err_out_free_bio:
    + bio_put(bio);
    +err_out_free_cmp:
    + kfree(cmp);
    +err_out_exit:
    + if (err)
    + dst_mirror_mark_notsync(n);
    + return err;
    +}
    +
    +static int dst_mirror_ndp_setup(struct dst_node *n, int first_node, int clean_on_sync)
    +{
    + struct dst_mirror_priv *p = n->priv;
    + int sync = 1, err;
    + struct dst_mirror_priv *fp = p;
    + struct dst_node *first;
    +
    + p->full_resync = 0;
    +
    + if (first_node) {
    + u64 new_age = *(u64 *)&n->st;
    +
    + p->old_age = p->data.age;
    + printk(KERN_NOTICE "%s: first age: %llx -> %llx. "
    + "Old will be set to new for the first node.\n",
    + __func__, p->old_age, new_age);
    + p->data.age = new_age;
    +
    + err = dst_mirror_write_node_data(n, &p->data);
    + if (err)
    + return err;
    + } else {
    + mutex_lock(&n->st->tree_lock);
    + first = dst_storage_tree_search(n->st, n->start);
    + if (!first) {
    + mutex_unlock(&n->st->tree_lock);
    + dprintk("%s: there are no nodes in the storage.\n", __func__);
    + return -ENODEV;
    + }
    +
    + fp = first->priv;
    +
    + if (fp->old_age != p->data.age) {
    + p->full_resync = 1;
    + sync = 0;
    + }
    +
    + p->old_age = fp->old_age;
    +
    + n->shared_head = first;
    + atomic_inc(&first->shared_num);
    + list_add_tail(&n->shared, &first->shared);
    + mutex_unlock(&n->st->tree_lock);
    +
    + if (sync) {
    + unsigned long flags;
    + unsigned int pidx, pnum;
    +
    + err = dst_mirror_process_log_on_disk(n, READ);
    + if (err)
    + goto err_out_put;
    +
    + spin_lock_irqsave(&fp->log_lock, flags);
    + if (fp->data.write_idx != p->data.write_idx)
    + sync = 0;
    + spin_unlock_irqrestore(&fp->log_lock, flags);
    +
    + pnum = p->data.resync_idx / DST_LOG_ENTRIES_PER_PAGE;
    + pidx = p->data.resync_idx % DST_LOG_ENTRIES_PER_PAGE;
    +
    + if (p->log.entries[pnum][pidx].error)
    + sync = 0;
    + }
    + }
    +
    + if (!sync) {
    + printk(KERN_NOTICE "%s: node %llu:%llu is not synced with the first one: "
    + "first_age: %llx, new_age: %llx, indexes %s.\n",
    + __func__, n->start, n->start+n->size,
    + p->data.age, p->old_age,
    + p->full_resync ? "does not match" : "match");
    + dst_mirror_mark_notsync(n);
    + } else {
    + if (clean_on_sync)
    + dst_mirror_mark_node_sync(n);
    + complete(&p->resync_complete);
    +
    + printk(KERN_NOTICE "%s: node %llu:%llu is in sync with the first node.\n",
    + __func__, n->start, n->start+n->size);
    + }
    +
    + dprintk("%s: age: old: %llx, new: %llx.\n", __func__, p->old_age, fp->data.age);
    +
    + return 0;
    +
    +err_out_put:
    + first = n->shared_head;
    + atomic_dec(&first->shared_num);
    + mutex_lock(&n->st->tree_lock);
    + list_del(&n->shared);
    + n->shared_head = NULL;
    + mutex_unlock(&n->st->tree_lock);
    + dst_node_put(first);
    +
    + return err;
    +}
    +
    +static int dst_mirror_end_io(struct bio *bio, unsigned int size, int err)
    +{
    + struct dst_request *req = bio->bi_private;
    +
    + if (bio->bi_size)
    + return 0;
    +
    + dprintk("%s: req: %p, bio: %p, req->bio: %p, err: %d.\n",
    + __func__, req, bio, req->bio, err);
    + req->bio_endio(req, err);
    + bio_put(bio);
    + return 0;
    +}
    +
    +static int dst_mirror_process_request_nosync(struct dst_request *req,
    + struct dst_node *n)
    +{
    + int err = 0;
    +
    + /*
    + * Block layer requires to clone a bio.
    + */
    + if (n->bdev) {
    + struct bio *clone = bio_alloc_bioset(GFP_NOIO,
    + req->bio->bi_max_vecs, dst_mirror_bio_set);
    +
    + __bio_clone(clone, req->bio);
    +
    + clone->bi_bdev = n->bdev;
    + clone->bi_destructor = dst_mirror_destructor;
    + clone->bi_private = req;
    + clone->bi_end_io = &dst_mirror_end_io;
    +
    + dprintk("%s: clone: %p, bio: %p, req: %p.\n",
    + __func__, clone, req->bio, req);
    +
    + generic_make_request(clone);
    + err = 1;
    + } else {
    + struct dst_request nr;
    + /*
    + * Network state processing engine will clone request
    + * by itself if needed. We can not use the same structure
    + * here, since number of its fields will be modified.
    + */
    + memcpy(&nr, req, sizeof(struct dst_request));
    +
    + nr.node = n;
    + nr.state = n->state;
    + nr.priv = req;
    +
    + err = kst_check_permissions(n->state, req->bio);
    + if (!err)
    + err = n->state->ops->push(&nr);
    + }
    +
    + dprintk("%s: req: %p, n: %p, bdev: %p, err: %d.\n",
    + __func__, req, n, n->bdev, err);
    +
    + return err;
    +}
    +
    +static int dst_mirror_sync_requeue(struct dst_node *n, int exiting)
    +{
    + struct dst_mirror_priv *p = n->priv;
    + struct dst_mirror_sync_container *sc;
    + struct dst_request req;
    + unsigned long flags;
    + int err, num = 0;
    +
    + if (!list_empty(&p->backlog_list))
    + dprintk("%s: n: %p, backlog_empty: %d, resync_num: %d.\n",
    + __func__, n, list_empty(&p->backlog_list),
    + atomic_read(&p->resync_num));
    +
    + while (!list_empty(&p->backlog_list)) {
    + sc = NULL;
    + spin_lock_irqsave(&p->backlog_lock, flags);
    + if (!list_empty(&p->backlog_list)) {
    + sc = list_entry(p->backlog_list.next,
    + struct dst_mirror_sync_container,
    + sync_entry);
    + if (bio_rw(sc->bio) == WRITE)
    + list_del(&sc->sync_entry);
    + else
    + sc = NULL;
    + }
    + spin_unlock_irqrestore(&p->backlog_lock, flags);
    +
    + if (!sc)
    + break;
    +
    + sc->bio->bi_private = n;
    + if (sc->bio->bi_size == 0 || exiting) {
    + err = -EIO;
    + goto out;
    + }
    +
    + memset(&req, 0, sizeof(struct dst_request));
    + dst_fill_request(&req, sc->bio, sc->start - n->start,
    + n, &kst_bio_endio);
    +
    + err = dst_mirror_process_request_nosync(&req, n);
    +out:
    + if (err < 0)
    + bio_endio(sc->bio, sc->bio->bi_size, err);
    + kfree(sc);
    + num++;
    + }
    +
    + return num;
    +}
    +
    +
    +static void dst_mirror_resync_work(struct work_struct *work)
    +{
    + struct dst_mirror_priv *priv = container_of(work,
    + struct dst_mirror_priv, resync_work.work);
    + struct dst_node *n = priv->node;
    +
    + dst_mirror_resync(n, 0);
    + dst_mirror_sync_requeue(n, 0);
    + schedule_delayed_work(&priv->resync_work, priv->resync_timeout);
    +}
    +
    +/*
    + * Mirroring log is used to store write request information.
    + * It is allocated on disk and in memory (sync happens each time
    + * resync work queue fires), and eats about 1% of free RAM or disk
    + * (what is less). Each write updates log, so when node goes offline,
    + * its log will be updated with error values, so that this entries
    + * could be resynced when node will be back online. When number of
    + * failed writes becomes equal to number of entries in the write log,
    + * recovery becomes impossible (since old log entries were overwritten)
    + * and full resync is scheduled.
    + *
    + * This does not work well with the situation, when there are multiple
    + * writes to the same locations - they are considered as different
    + * writes and thus will be resynced multiple times.
    + * The right solution is to check log for each write, better if log
    + * would be not array, but tree.
    + */
    +static int dst_mirror_log_init(struct dst_node *n)
    +{
    + struct dst_mirror_priv *priv = n->priv;
    + struct dst_mirror_log *log = &priv->log;
    + struct dst_mirror_node_data *pd = &priv->data;
    + u64 allowed_ram = DIV_ROUND_UP(global_page_state(NR_FREE_PAGES), 100);
    + u64 allowed_disk = DIV_ROUND_UP(to_bytes(n->size), 100);
    + u64 num;
    + unsigned int nr_pages, i;
    + int err;
    +
    + err = dst_mirror_read_node_data(n, pd);
    + if (err)
    + return err;
    +
    + allowed_ram <<= PAGE_SHIFT;
    +
    + num = min(allowed_disk, allowed_ram)/sizeof(struct dst_write_entry);
    + nr_pages = min(allowed_disk, allowed_ram) >> PAGE_SHIFT;
    +
    + log->entries = kzalloc(nr_pages * sizeof(void *), GFP_KERNEL);
    + if (!log->entries)
    + return -ENOMEM;
    +
    + for (i=0; i<nr_pages; ++i) {
    + log->entries[i] = kzalloc(PAGE_SIZE, GFP_KERNEL);
    + if (!log->entries[i])
    + goto err_out_free;
    + }
    +
    + log->nr_pages = nr_pages;
    +
    + pd->num = num;
    + pd->write_idx = pd->resync_idx = 0;
    +
    + printk(KERN_INFO "%s: mirror write log contains %llu entries (%u pages).\n",
    + __func__, num, nr_pages);
    +
    + return 0;
    +
    +err_out_free:
    + while (i-- != 0)
    + kfree(log->entries[i]);
    + kfree(log->entries);
    +
    + return -ENOMEM;
    +}
    +
    +static void dst_mirror_log_exit(struct dst_node *n)
    +{
    + struct dst_mirror_priv *priv = n->priv;
    + unsigned int i;
    +
    + for (i=0; i<priv->log.nr_pages; ++i)
    + kfree(priv->log.entries[i]);
    + kfree(priv->log.entries);
    +}
    +
    +/*
    + * This callback is invoked when node is added to storage.
    + */
    +static int dst_mirror_add_node(struct dst_node *n)
    +{
    + struct dst_storage *st = n->st;
    + struct dst_mirror_priv *priv;
    + int err = -ENOMEM, first_node = 0;
    + u64 disk_size;
    +
    + n->size--; /* A sector size actually. */
    +
    + priv = kzalloc(sizeof(struct dst_mirror_priv), GFP_KERNEL);
    + if (!priv)
    + return -ENOMEM;
    +
    + priv->ndp_sector = n->size;
    + priv->node = n;
    + priv->resync_start = 0;
    + priv->resync_size = to_sector(1024*1024*100ULL);
    + init_completion(&priv->resync_complete);
    + atomic_set(&priv->resync_num, 0);
    + INIT_DELAYED_WORK(&priv->resync_work, dst_mirror_resync_work);
    + priv->resync_timeout = 1000;
    +
    + spin_lock_init(&priv->resync_wait_lock);
    + INIT_LIST_HEAD(&priv->resync_wait_list);
    + priv->resync_wait_num = 0;
    +
    + spin_lock_init(&priv->backlog_lock);
    + INIT_LIST_HEAD(&priv->backlog_list);
    +
    + n->priv_callback = &dst_mirror_handle_priv;
    + n->priv = priv;
    +
    + spin_lock_init(&priv->log_lock);
    +
    + err = dst_mirror_log_init(n);
    + if (err)
    + goto err_out_free;
    +
    + n->size -= to_sector(priv->log.nr_pages << PAGE_SHIFT);
    +
    + mutex_lock(&st->tree_lock);
    + disk_size = st->disk_size;
    + if (st->disk_size) {
    + st->disk_size = min(n->size, st->disk_size);
    + } else {
    + st->disk_size = n->size;
    + first_node = 1;
    + }
    + mutex_unlock(&st->tree_lock);
    +
    + err = dst_mirror_ndp_setup(n, first_node, 1);
    + if (err)
    + goto err_out_free_log;
    +
    + schedule_delayed_work(&priv->resync_work, priv->resync_timeout);
    +
    + dprintk("%s: n: %p, %llu:%llu, disk_size: %llu.\n",
    + __func__, n, n->start, n->size, st->disk_size);
    +
    + return 0;
    +
    +err_out_free_log:
    + mutex_lock(&st->tree_lock);
    + st->disk_size = disk_size;
    + mutex_unlock(&st->tree_lock);
    + dst_mirror_log_exit(n);
    +err_out_free:
    + kfree(priv);
    + n->priv = NULL;
    + return err;
    +}
    +
    +static void dst_mirror_sync_destructor(struct bio *bio)
    +{
    + struct bio_vec *bv;
    + int i;
    +
    + bio_for_each_segment(bv, bio, i)
    + __free_page(bv->bv_page);
    + bio_free(bio, dst_mirror_bio_set);
    +}
    +
    +static void dst_mirror_check_resync_complete(struct dst_node *n, int num_completed)
    +{
    + struct dst_mirror_priv *priv = n->priv;
    +
    + if (atomic_sub_return(num_completed, &priv->resync_num) == 0) {
    + dprintk("%s: completing resync request, start: %llu, size: %llu.\n",
    + __func__, priv->resync_start, priv->resync_size);
    + complete(&priv->resync_complete);
    + if (!priv->full_resync)
    + schedule_delayed_work(&priv->resync_work, 0);
    + }
    +}
    +
    +static int dst_mirror_sync_check(struct dst_node *n)
    +{
    + struct dst_mirror_priv *priv = n->priv;
    + struct dst_mirror_node_data *pd = &priv->data;
    + unsigned int pidx, pnum, i, j;
    + struct dst_write_entry *e;
    +
    + pnum = pd->resync_idx / DST_LOG_ENTRIES_PER_PAGE;
    + pidx = pd->resync_idx % DST_LOG_ENTRIES_PER_PAGE;
    +
    + for (i=pnum; i<priv->log.nr_pages; ++i) {
    + for (j=pidx; j<DST_LOG_ENTRIES_PER_PAGE; ++j) {
    + e = &priv->log.entries[i][j];
    +
    + if (e->error) {
    + pd->resync_idx = i*DST_LOG_ENTRIES_PER_PAGE + j;
    + return 1;
    + }
    + }
    +
    + pidx = 0;
    + }
    +
    + dst_mirror_mark_node_sync(n);
    + return 0;
    +}
    +
    +static int dst_mirror_sync_endio(struct bio *bio, unsigned int size, int err)
    +{
    + dprintk("%s: bio: %p, err: %d, size: %u, op: %s.\n",
    + __func__, bio, err, bio->bi_size,
    + (bio_rw(bio) != WRITE)?"read":"write");
    +
    + if (bio->bi_size)
    + return 1;
    +
    + if (bio_rw(bio) != WRITE) {
    + struct dst_mirror_sync_container *sc = bio->bi_private;
    +
    + if (err)
    + dst_mirror_mark_notsync(sc->node);
    +
    + if (!err) {
    + bio->bi_size = sc->size;
    + bio->bi_sector = sc->start;
    + }
    + bio->bi_rw = WRITE;
    + } else {
    + struct dst_node *n = bio->bi_private;
    + struct dst_mirror_priv *priv = n->priv;
    +
    + if (err)
    + dst_mirror_mark_notsync(n);
    + else if (!priv->full_resync) {
    + struct dst_mirror_node_data *pd = &priv->data;
    + unsigned long flags;
    +
    + spin_lock_irqsave(&priv->log_lock, flags);
    + pd->resync_idx = (pd->resync_idx + 1) % pd->num;
    + dst_mirror_sync_check(n);
    + spin_unlock_irqrestore(&priv->log_lock, flags);
    + }
    + bio_put(bio);
    + dst_mirror_check_resync_complete(n, 1);
    + }
    +
    + return 0;
    +}
    +
    +static int dst_mirror_sync_block(struct dst_node *n,
    + u64 start, u32 size)
    +{
    + struct bio *bio;
    + unsigned int nr_pages = DIV_ROUND_UP(size, PAGE_SIZE), i, nr;
    + struct page *page;
    + int err = -ENOMEM;
    + unsigned long flags;
    + struct dst_mirror_sync_container *sc;
    + struct dst_mirror_priv *priv = n->priv;
    +
    + dprintk("%s: [all in sectors] start: %llu, size: %u, nr_pages: %u, disk_size: %llu.\n",
    + __func__, (u64)to_sector(start), (unsigned int)to_sector(size),
    + nr_pages, n->st->disk_size);
    +
    + atomic_set(&priv->resync_num, nr_pages);
    +
    + while (nr_pages) {
    + nr = min_t(unsigned int, nr_pages, BIO_MAX_PAGES);
    +
    + sc = kmalloc(sizeof(struct dst_mirror_sync_container), GFP_KERNEL);
    + if (!sc)
    + return -ENOMEM;
    +
    + bio = bio_alloc_bioset(GFP_NOIO, nr, dst_mirror_bio_set);
    + if (!bio)
    + goto err_out_free_sc;
    +
    + bio->bi_rw = READ;
    + bio->bi_private = sc;
    + bio->bi_sector = to_sector(start);
    + bio->bi_bdev = NULL;
    + bio->bi_destructor = dst_mirror_sync_destructor;
    + bio->bi_end_io = dst_mirror_sync_endio;
    +
    + for (i = 0; i < nr; ++i) {
    + page = alloc_page(GFP_NOIO);
    + if (!page)
    + break;
    +
    + err = bio_add_pc_page(n->st->queue, bio, page,
    + min_t(u32, PAGE_SIZE, size), 0);
    + if (err <= 0)
    + break;
    + size -= err;
    + err = 0;
    + }
    +
    + if (!bio->bi_vcnt) {
    + err = -ENOMEM;
    + goto err_out_put_bio;
    + }
    +
    + sc->node = n;
    + sc->bio = bio;
    + sc->start = bio->bi_sector;
    + sc->size = bio->bi_size;
    +
    + dst_mirror_check_resync_complete(n, i-1);
    +
    + spin_lock_irqsave(&priv->backlog_lock, flags);
    + list_add_tail(&sc->sync_entry, &priv->backlog_list);
    + spin_unlock_irqrestore(&priv->backlog_lock, flags);
    +
    + nr_pages -= bio->bi_vcnt;
    + dprintk("%s: start: %llu, size: %u/%u, bio: %p, rest_pages: %u, rest_bytes: %u.\n",
    + __func__, start, bio->bi_size, nr, bio, nr_pages, size);
    +
    + start += bio->bi_size;
    +
    + err = n->st->queue->make_request_fn(n->st->queue, bio);
    + if (err)
    + goto err_out_del;
    + }
    +
    + return 0;
    +
    +err_out_del:
    + spin_lock_irqsave(&priv->backlog_lock, flags);
    + list_del(&sc->sync_entry);
    + spin_unlock_irqrestore(&priv->backlog_lock, flags);
    +err_out_put_bio:
    + bio_put(bio);
    +err_out_free_sc:
    + kfree(sc);
    + return err;
    +}
    +
    +static void dst_mirror_read_endio(struct dst_request *req, int err)
    +{
    + if (err)
    + dst_mirror_mark_notsync(req->node);
    +
    + if (err && req->state)
    + kst_wake(req->state);
    +
    + if (!err || req->callback)
    + kst_bio_endio(req, err);
    +}
    +
    +static void dst_mirror_update_write_log(struct dst_request *req, int err)
    +{
    + struct dst_mirror_priv *priv = req->node->priv;
    + struct dst_mirror_log *log = &priv->log;
    + struct dst_mirror_node_data *pd = &priv->data;
    + unsigned long flags;
    + struct dst_write_entry *e;
    + unsigned int pnum, idx;
    +
    + spin_lock_irqsave(&priv->log_lock, flags);
    +
    + pnum = pd->write_idx / DST_LOG_ENTRIES_PER_PAGE;
    + idx = pd->write_idx % DST_LOG_ENTRIES_PER_PAGE;
    +
    + e = &log->entries[pnum][idx];
    + e->error = err;
    + e->start = req->start - to_sector(req->orig_size);
    + e->size = req->orig_size;
    +
    + if (++pd->write_idx == pd->num)
    + pd->write_idx = 0;
    +
    + if (test_bit(DST_NODE_NOTSYNC, &req->node->flags) &&
    + pd->write_idx == pd->resync_idx)
    + priv->full_resync = 1;
    +
    + spin_unlock_irqrestore(&priv->log_lock, flags);
    +}
    +
    +static void dst_mirror_write_endio(struct dst_request *req, int err)
    +{
    + if (err) {
    + dst_mirror_mark_notsync(req->node);
    + if (req->state)
    + kst_wake(req->state);
    + }
    + dst_mirror_update_write_log(req, err);
    +
    + req = req->priv;
    +
    + dprintk("%s: req: %p, priv: %p err: %d, bio: %p, "
    + "cnt: %d, orig_size: %llu.\n",
    + __func__, req, req->priv, err, req->bio,
    + atomic_read(&req->refcnt), req->orig_size);
    +
    + if (atomic_dec_and_test(&req->refcnt)) {
    + bio_endio(req->bio, req->orig_size, 0);
    + dst_free_request(req);
    + }
    +}
    +
    +static int dst_mirror_process_request(struct dst_request *req,
    + struct dst_node *n)
    +{
    + int err;
    +
    + dst_mirror_sync_requeue(n, 0);
    + err = dst_mirror_process_request_nosync(req, n);
    + if (err > 0)
    + err = 0;
    + if (err)
    + req->bio_endio(req, err);
    +
    + return err;
    +}
    +
    +static int dst_mirror_write(struct dst_request *oreq)
    +{
    + struct dst_node *n, *node = oreq->node;
    + struct dst_request *req = oreq;
    + int num, err = 0, err_num = 0, orig_num;
    + struct dst_mirror_priv *priv = node->priv;
    + unsigned long flags;
    +
    + /*
    + * This check is for requests which fell into resync window.
    + * Such requests are written when resync window moves forward.
    + */
    + if (oreq->bio_endio != &dst_mirror_write_endio) {
    + req = dst_clone_request(oreq, oreq->node->w->req_pool);
    + if (!req) {
    + err = -ENOMEM;
    + goto err_out_exit;
    + }
    +
    + req->priv = req;
    + req->bio_endio = &dst_mirror_write_endio;
    + }
    +
    + if (test_bit(DST_NODE_NOTSYNC, &node->flags) &&
    + oreq->start >= priv->resync_start &&
    + to_sector(oreq->orig_size) <= priv->resync_size &&
    + priv->full_resync) {
    + dprintk("%s: queueing request: start: %llu, size: %llu, resync window start: %llu, size: %llu.\n",
    + __func__, oreq->start, (u64)to_sector(oreq->orig_size),
    + priv->resync_start, priv->resync_size);
    + spin_lock_irqsave(&priv->resync_wait_lock, flags);
    + list_add_tail(&req->request_list_entry, &priv->resync_wait_list);
    + priv->resync_wait_num++;
    + spin_unlock_irqrestore(&priv->resync_wait_lock, flags);
    + return 0;
    + }
    +
    + /*
    + * This logic is pretty simple - req->bio_endio will not
    + * call bio_endio() until all mirror devices completed
    + * processing of the request (no matter with or without error).
    + * Mirror's req->bio_endio callback will take care of that.
    + */
    + orig_num = num = atomic_read(&req->node->shared_num) + 1;
    + atomic_set(&req->refcnt, num);
    +
    + dprintk("\n%s: req: %p, mirror to %d nodes.\n",
    + __func__, req, num);
    +
    + err = dst_mirror_process_request(req, node);
    + if (err)
    + err_num++;
    +
    + if (--num) {
    + list_for_each_entry(n, &node->shared, shared) {
    + dprintk("\n%s: req: %p, start: %llu, size: %llu, "
    + "num: %d, n: %p, state: %p.\n",
    + __func__, req, req->start,
    + req->size, num, n, n->state);
    +
    + err = dst_mirror_process_request(req, n);
    + if (err)
    + err_num++;
    +
    + if (--num <= 0)
    + break;
    + }
    + }
    +
    + if (err_num == orig_num)
    + dprintk("%s: req: %p, num: %d, err: %d.\n",
    + __func__, req, num, err);
    +
    + err = 0;
    +
    +err_out_exit:
    + return err;
    +}
    +
    +static int dst_mirror_read(struct dst_request *req)
    +{
    + struct dst_node *node = req->node, *n, *min_dist_node;
    + struct dst_mirror_priv *priv = node->priv;
    + u64 dist, d;
    + int err;
    +
    + req->bio_endio = &dst_mirror_read_endio;
    +
    + do {
    + err = -ENODEV;
    + min_dist_node = NULL;
    + dist = -1ULL;
    +
    + /*
    + * Reading is never performed from the node under resync.
    + */
    +
    + if (!test_bit(DST_NODE_NOTSYNC, &node->flags)) {
    + priv = node->priv;
    + if (req->start > priv->last_start)
    + dist = req->start - priv->last_start;
    + else
    + dist = priv->last_start - req->start;
    + min_dist_node = req->node;
    + }
    +
    + list_for_each_entry(n, &node->shared, shared) {
    + if (test_bit(DST_NODE_NOTSYNC, &n->flags))
    + continue;
    +
    + priv = n->priv;
    +
    + if (req->start > priv->last_start)
    + d = req->start - priv->last_start;
    + else
    + d = priv->last_start - req->start;
    +
    + if (d < dist)
    + min_dist_node = n;
    + }
    +
    + if (!min_dist_node)
    + break;
    +
    + priv = min_dist_node->priv;
    + priv->last_start = req->start;
    +
    + req->node = min_dist_node;
    + req->state = req->node->state;
    +
    + if (req->node->bdev) {
    + req->bio->bi_bdev = req->node->bdev;
    + generic_make_request(req->bio);
    + err = 0;
    + break;
    + }
    +
    + err = req->state->ops->push(req);
    + if (err) {
    + dprintk("%s: req: %p, bio: %p, node: %p, err: %d.\n",
    + __func__, req, req->bio, min_dist_node, err);
    + dst_mirror_mark_notsync(req->node);
    + }
    + } while (err && min_dist_node);
    +
    + if (err || !min_dist_node) {
    + dprintk("%s: req: %p, bio: %p, node: %p, err: %d.\n",
    + __func__, req, req->bio, min_dist_node, err);
    + if (!err)
    + err = -ENODEV;
    + }
    + dprintk("%s: req: %p, err: %d.\n", __func__, req, err);
    + return err;
    +}
    +
    +/*
    + * This callback is invoked from block layer request processing function,
    + * its task is to remap block request to different nodes.
    + */
    +static int dst_mirror_remap(struct dst_request *req)
    +{
    + int (*remap[])(struct dst_request *) =
    + {&dst_mirror_read, &dst_mirror_write};
    +
    + return remap[bio_rw(req->bio) == WRITE](req);
    +}
    +
    +static void dst_mirror_write_queued(struct dst_node *n)
    +{
    + struct dst_mirror_priv *priv = n->priv;
    + unsigned long flags;
    + struct dst_request *req;
    + int num = priv->resync_wait_num, err;
    +
    + while (!list_empty(&priv->resync_wait_list) && num != 0) {
    + req = NULL;
    + spin_lock_irqsave(&priv->resync_wait_lock, flags);
    + if (!list_empty(&priv->resync_wait_list)) {
    + req = list_entry(priv->resync_wait_list.next,
    + struct dst_request,
    + request_list_entry);
    + list_del_init(&req->request_list_entry);
    + num--;
    + }
    + spin_unlock_irqrestore(&priv->resync_wait_lock, flags);
    +
    + if (!req)
    + break;
    +
    + dprintk("%s: queued request n: %p, req: %p, start: %llu, size: %llu, num: %d.\n",
    + __func__, n, req, req->start, (u64)to_sector(req->size), num);
    + err = dst_mirror_process_request(req, n);
    + if (err)
    + break;
    + }
    +}
    +
    +static int dst_mirror_resync_partial(struct dst_node *node)
    +{
    + struct dst_storage *st = node->st;
    + struct dst_node *first = node->shared_head, *n, *sync;
    + struct dst_mirror_priv *p = node->priv, *sp;
    + struct dst_mirror_node_data *pd = &p->data;
    + struct dst_mirror_node_data *spd;
    + struct dst_write_entry *e, *ep;
    + unsigned long flags;
    + unsigned int pnum, idx;
    + u64 start;
    + u32 size;
    +
    + if (!first)
    + first = node;
    +
    + sync = NULL;
    + mutex_lock(&st->tree_lock);
    + list_for_each_entry(n, &first->shared, shared) {
    + if (!test_bit(DST_NODE_NOTSYNC, &n->flags)) {
    + sync = n;
    + dst_node_get(sync);
    + break;
    + }
    + }
    + mutex_unlock(&st->tree_lock);
    + dprintk("%s: n: %p, first: %p, sync: %p.\n", __func__, node, first, sync);
    +
    + if (!sync)
    + return -ENODEV;
    +
    + sp = sync->priv;
    + spd = &sp->data;
    +
    + spin_lock_irqsave(&sp->log_lock, flags);
    + spin_lock(&p->log_lock);
    +
    + pnum = pd->resync_idx / DST_LOG_ENTRIES_PER_PAGE;
    + idx = pd->resync_idx % DST_LOG_ENTRIES_PER_PAGE;
    +
    + ep = sp->log.entries[pnum];
    + e = &ep[idx];
    +
    + start = e->start;
    + size = e->size;
    +
    + spin_unlock(&p->log_lock);
    + spin_unlock_irqrestore(&sp->log_lock, flags);
    +
    + dprintk("%s: node write_idx: %llu, resync_idx: %llu, num: %llu, sync write_idx: %llu, num: %llu.\n",
    + __func__, pd->write_idx, pd->resync_idx, pd->num, spd->write_idx, spd->num);
    + dprintk("%s: sync request: start: %llu, size: %llu.\n",
    + __func__, start, (u64)to_sector(size));
    +
    + dst_node_put(sync);
    +
    + return dst_mirror_sync_block(node, to_bytes(start), size);
    +}
    +
    +/*
    + * Resync logic - sliding window algorithm.
    + *
    + * At startup system checks age (unique cookie) of the node and if it
    + * does not match first node it resyncs all data from the first node in
    + * the mirror to others (non-sync nodes), each non-synced node has a
    + * window, which slides from the start of the node to the end.
    + * During resync all requests, which enter the window are queued, thus
    + * window has to be sufficiently small. When window is synced from the
    + * other nodes, queued requests are written and window moves forward,
    + * thus subsequent resync is started when previous window is fully completed.
    + * When window reaches end of the node, it is marked as synchronized.
    + *
    + * If age of the node matches the first one, but log contains different
    + * number of write log entries compared to the first node (first node always
    + * stands as a clean), then partial resync is scheduled.
    + * Partial resync will also be scheduled when log entry pointed by resync
    + * index of the node contains error.
    + *
    + * Mechanism of this resync type is following: system selects a sync node
    + * (checking each node's flags) and fetches a log entry pointed by resync
    + * index of the given node and resync data from other nodes to given one.
    + * Then it checks the rest of the write log and checks if there are
    + * another failed writes, so that next resync block would be fetched for
    + * them.
    + */
    +static int dst_mirror_resync(struct dst_node *n, int ndp)
    +{
    + struct dst_mirror_priv *priv = n->priv;
    + struct dst_mirror_priv *fp = priv;
    + u64 total, allowed, size;
    + int err;
    +
    + if (n->shared_head)
    + fp = n->shared_head->priv;
    +
    + if (!test_bit(DST_NODE_NOTSYNC, &n->flags))
    + return 0;
    + if (atomic_read(&priv->resync_num) != 0) {
    + dprintk("%s: n: %p, resync_num: %d.\n",
    + __func__, n, atomic_read(&priv->resync_num));
    + return -EAGAIN;
    + }
    +
    + allowed = global_page_state(NR_FREE_PAGES) +
    + global_page_state(NR_FILE_PAGES);
    + allowed /= 2;
    + allowed = to_sector(allowed << PAGE_SHIFT);
    +
    + size = min(priv->resync_size, n->size - priv->resync_start);
    +
    + total = min(allowed, size);
    +
    + printk(KERN_NOTICE "%s: node: %p, %llu:%llu %s synchronization has been started "
    + "from %llu, allowed: %llu, total: %llu.\n",
    + __func__, n, n->start, n->size,
    + (priv->data.age == fp->data.age) ? "partial" : "full",
    + priv->resync_start, allowed, total);
    +
    + if (!priv->full_resync)
    + return dst_mirror_resync_partial(n);
    +
    + dst_mirror_write_queued(n);
    +
    + if (priv->resync_start == n->size) {
    + dst_mirror_mark_node_sync(n);
    + priv->data.age = fp->data.age;
    + dst_mirror_write_node_data(n, &priv->data);
    + return 0;
    + }
    +
    + if (ndp) {
    + err = dst_mirror_ndp_setup(n, 0, 0);
    + if (err)
    + return err;
    + }
    +
    + err = dst_mirror_sync_block(n, to_bytes(priv->resync_start),
    + to_bytes(total));
    + if (!err)
    + priv->resync_start += total;
    +
    + return err;
    +}
    +
    +static int dst_mirror_error(struct kst_state *st, int err)
    +{
    + struct dst_request *req, *tmp;
    + unsigned int revents = st->socket->ops->poll(NULL, st->socket, NULL);
    +
    + dprintk("%s: err: %d, revents: %x, notsync: %d.\n",
    + __func__, err, revents,
    + test_bit(DST_NODE_NOTSYNC, &st->node->flags));
    +
    + if (err == -EEXIST)
    + return err;
    +
    + if (!(revents & (POLLERR | POLLHUP)) &&
    + (err == -EPIPE || err == -ECONNRESET)) {
    + if (test_bit(DST_NODE_NOTSYNC, &st->node->flags))
    + return dst_mirror_resync(st->node, 1);
    + return 0;
    + }
    +
    + if (atomic_read(&st->node->shared_num) == 0 &&
    + !st->node->shared_head) {
    + dprintk("%s: this node is the only one in the mirror, "
    + "can not mark it notsync.\n", __func__);
    + return err;
    + }
    +
    + dst_mirror_mark_notsync(st->node);
    +
    + mutex_lock(&st->request_lock);
    + list_for_each_entry_safe(req, tmp, &st->request_list,
    + request_list_entry) {
    + kst_del_req(req);
    + dprintk("%s: requeue [%c], start: %llu, idx: %d,"
    + " num: %d, size: %llu, offset: %u, err: %d.\n",
    + __func__, (bio_rw(req->bio) == WRITE)?'W':'R',
    + req->start, req->idx, req->num, req->size,
    + req->offset, err);
    +
    + if (bio_rw(req->bio) != WRITE) {
    + req->start -= to_sector(req->orig_size - req->size);
    + req->size = req->orig_size;
    + req->flags &= ~(DST_REQ_HEADER_SENT | DST_REQ_CHEKSUM_RECV);
    + req->idx = 0;
    + if (dst_mirror_read(req))
    + dst_free_request(req);
    + } else {
    + kst_complete_req(req, err);
    + }
    + }
    + mutex_unlock(&st->request_lock);
    + return err;
    +}
    +
    +/*
    + * This callback is invoked when node is removed from storage.
    + */
    +static void dst_mirror_del_node(struct dst_node *n)
    +{
    + struct dst_mirror_priv *priv = n->priv;
    +
    + priv->full_resync = 1;
    + cancel_rearming_delayed_work(&priv->resync_work);
    + flush_scheduled_work();
    +
    + dprintk("%s: n: %p, backlog_empty: %d, resync_num: %d.\n",
    + __func__, n, list_empty(&priv->backlog_list),
    + atomic_read(&priv->resync_num));
    +
    + /*
    + * This strange-looking loop waits until all resync read requests
    + * are completed, this happens in dst_mirror_sync_requeue().
    + */
    + while (atomic_read(&priv->resync_num)) {
    + dst_mirror_sync_requeue(n, 1);
    + if (printk_ratelimit())
    + dprintk("%s: n: %p, backlog_empty: %d, resync_num: %d.\n",
    + __func__, n, list_empty(&priv->backlog_list),
    + atomic_read(&priv->resync_num));
    + msleep(100);
    + }
    +
    + wait_for_completion(&priv->resync_complete);
    + dst_mirror_sync_requeue(n, 1);
    +
    + if (priv) {
    + dst_mirror_log_exit(n);
    + kfree(priv);
    + n->priv = NULL;
    + }
    +
    + if (n->device.parent == &n->st->device) {
    + int i;
    +
    + for (i=0; i<ARRAY_SIZE(dst_mirror_attrs); ++i)
    + device_remove_file(&n->device, &dst_mirror_attrs[i]);
    + }
    +}
    +
    +static struct dst_alg_ops alg_mirror_ops = {
    + .remap = dst_mirror_remap,
    + .add_node = dst_mirror_add_node,
    + .del_node = dst_mirror_del_node,
    + .error = dst_mirror_error,
    + .owner = THIS_MODULE,
    +};
    +
    +static int __devinit alg_mirror_init(void)
    +{
    + int err = -ENOMEM;
    +
    + dst_mirror_bio_set = bioset_create(256, 256);
    + if (!dst_mirror_bio_set)
    + return -ENOMEM;
    +
    + alg_mirror = dst_alloc_alg("alg_mirror", &alg_mirror_ops);
    + if (!alg_mirror)
    + goto err_out;
    +
    + return 0;
    +
    +err_out:
    + bioset_free(dst_mirror_bio_set);
    + return err;
    +}
    +
    +static void __devexit alg_mirror_exit(void)
    +{
    + dst_remove_alg(alg_mirror);
    + bioset_free(dst_mirror_bio_set);
    +}
    +
    +module_init(alg_mirror_init);
    +module_exit(alg_mirror_exit);
    +
    +MODULE_LICENSE("GPL");
    +MODULE_AUTHOR("Evgeniy Polyakov <johnpol@2ka.mipt.ru>");
    +MODULE_DESCRIPTION("Mirror distributed algorithm.");


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      Last update: 2007-12-17 16:09    [W:0.123 / U:0.204 seconds]
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