Subject: [resend take 3 3/4] DST crypto thread pool.

From: Evgeniy Polyakov <[email-masked]>
Date: Tue, 25 Nov 2008 17:37:49 +0300

Signed-off-by: Evgeniy Polyakov <[email-masked]>

diff --git a/drivers/block/dst/crypto.c b/drivers/block/dst/crypto.c
new file mode 100644
index 0000000..7250f90
--- /dev/null
+++ b/drivers/block/dst/crypto.c
@@ -0,0 +1,731 @@
+/*
+ * 2007+ Copyright (c) Evgeniy Polyakov <[email-masked]>
+ * 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/bio.h>
+#include <linux/crypto.h>
+#include <linux/dst.h>
+#include <linux/kernel.h>
+#include <linux/scatterlist.h>
+#include <linux/slab.h>
+
+/*
+ * Tricky bastard, but IV can be more complex with time...
+ */
+static inline u64 dst_gen_iv(struct dst_trans *t)
+{
+	return t->gen;
+}
+
+/*
+ * Crypto machinery: hash/cipher support for the given crypto controls.
+ */
+static struct crypto_hash *dst_init_hash(struct dst_crypto_ctl *ctl, u8 *key)
+{
+	int err;
+	struct crypto_hash *hash;
+
+	hash = crypto_alloc_hash(ctl->hash_algo, 0, CRYPTO_ALG_ASYNC);
+	if (IS_ERR(hash)) {
+		err = PTR_ERR(hash);
+		dprintk("%s: failed to allocate hash '%s', err: %d.\n",
+				__func__, ctl->hash_algo, err);
+		goto err_out_exit;
+	}
+
+	ctl->crypto_attached_size = crypto_hash_digestsize(hash);
+
+	if (!ctl->hash_keysize)
+		return hash;
+
+	err = crypto_hash_setkey(hash, key, ctl->hash_keysize);
+	if (err) {
+		dprintk("%s: failed to set key for hash '%s', err: %d.\n",
+				__func__, ctl->hash_algo, err);
+		goto err_out_free;
+	}
+
+	return hash;
+
+err_out_free:
+	crypto_free_hash(hash);
+err_out_exit:
+	return ERR_PTR(err);
+}
+
+static struct crypto_ablkcipher *dst_init_cipher(struct dst_crypto_ctl *ctl, u8 *key)
+{
+	int err = -EINVAL;
+	struct crypto_ablkcipher *cipher;
+
+	if (!ctl->cipher_keysize)
+		goto err_out_exit;
+
+	cipher = crypto_alloc_ablkcipher(ctl->cipher_algo, 0, 0);
+	if (IS_ERR(cipher)) {
+		err = PTR_ERR(cipher);
+		dprintk("%s: failed to allocate cipher '%s', err: %d.\n",
+				__func__, ctl->cipher_algo, err);
+		goto err_out_exit;
+	}
+
+	crypto_ablkcipher_clear_flags(cipher, ~0);
+
+	err = crypto_ablkcipher_setkey(cipher, key, ctl->cipher_keysize);
+	if (err) {
+		dprintk("%s: failed to set key for cipher '%s', err: %d.\n",
+				__func__, ctl->cipher_algo, err);
+		goto err_out_free;
+	}
+
+	return cipher;
+
+err_out_free:
+	crypto_free_ablkcipher(cipher);
+err_out_exit:
+	return ERR_PTR(err);
+}
+
+/*
+ * Crypto engine has a pool of pages to encrypt data into before sending
+ * it over the network. This pool is freed/allocated here.
+ */
+static void dst_crypto_pages_free(struct dst_crypto_engine *e)
+{
+	unsigned int i;
+
+	for (i=0; i<e->page_num; ++i)
+		__free_page(e->pages[i]);
+	kfree(e->pages);
+}
+
+static int dst_crypto_pages_alloc(struct dst_crypto_engine *e, int num)
+{
+	int i;
+
+	e->pages = kmalloc(num * sizeof(struct page **), GFP_KERNEL);
+	if (!e->pages)
+		return -ENOMEM;
+
+	for (i=0; i<num; ++i) {
+		e->pages[i] = alloc_page(GFP_KERNEL);
+		if (!e->pages[i])
+			goto err_out_free_pages;
+	}
+
+	e->page_num = num;
+	return 0;
+
+err_out_free_pages:
+	while (--i >= 0)
+		__free_page(e->pages[i]);
+
+	kfree(e->pages);
+	return -ENOMEM;
+}
+
+/*
+ * Initialize crypto engine for given node.
+ * Setup cipher/hash, keys, pool of threads and private data.
+ */
+static int dst_crypto_engine_init(struct dst_crypto_engine *e, struct dst_node *n)
+{
+	int err;
+	struct dst_crypto_ctl *ctl = &n->crypto;
+
+	err = dst_crypto_pages_alloc(e, n->max_pages);
+	if (err)
+		goto err_out_exit;
+
+	e->size = PAGE_SIZE;
+	e->data = kmalloc(e->size, GFP_KERNEL);
+	if (!e->data) {
+		err = -ENOMEM;
+		goto err_out_free_pages;
+	}
+
+	if (ctl->hash_algo[0]) {
+		e->hash = dst_init_hash(ctl, n->hash_key);
+		if (IS_ERR(e->hash)) {
+			err = PTR_ERR(e->hash);
+			e->hash = NULL;
+			goto err_out_free;
+		}
+	}
+
+	if (ctl->cipher_algo[0]) {
+		e->cipher = dst_init_cipher(ctl, n->cipher_key);
+		if (IS_ERR(e->cipher)) {
+			err = PTR_ERR(e->cipher);
+			e->cipher = NULL;
+			goto err_out_free_hash;
+		}
+	}
+
+	return 0;
+
+err_out_free_hash:
+	crypto_free_hash(e->hash);
+err_out_free:
+	kfree(e->data);
+err_out_free_pages:
+	dst_crypto_pages_free(e);
+err_out_exit:
+	return err;
+}
+
+static void dst_crypto_engine_exit(struct dst_crypto_engine *e)
+{
+	if (e->hash)
+		crypto_free_hash(e->hash);
+	if (e->cipher)
+		crypto_free_ablkcipher(e->cipher);
+	dst_crypto_pages_free(e);
+	kfree(e->data);
+}
+
+/*
+ * Waiting for cipher processing to be completed.
+ */
+struct dst_crypto_completion
+{
+	struct completion		complete;
+	int				error;
+};
+
+static void dst_crypto_complete(struct crypto_async_request *req, int err)
+{
+	struct dst_crypto_completion *c = req->data;
+
+	if (err == -EINPROGRESS)
+		return;
+
+	dprintk("%s: req: %p, err: %d.\n", __func__, req, err);
+	c->error = err;
+	complete(&c->complete);
+}
+
+static int dst_crypto_process(struct ablkcipher_request *req,
+		struct scatterlist *sg_dst, struct scatterlist *sg_src,
+		void *iv, int enc, unsigned long timeout)
+{
+	struct dst_crypto_completion c;
+	int err;
+
+	init_completion(&c.complete);
+	c.error = -EINPROGRESS;
+
+	ablkcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
+					dst_crypto_complete, &c);
+
+	ablkcipher_request_set_crypt(req, sg_src, sg_dst, sg_src->length, iv);
+
+	if (enc)
+		err = crypto_ablkcipher_encrypt(req);
+	else
+		err = crypto_ablkcipher_decrypt(req);
+
+	switch (err) {
+		case -EINPROGRESS:
+		case -EBUSY:
+			err = wait_for_completion_interruptible_timeout(&c.complete,
+					timeout);
+			if (!err)
+				err = -ETIMEDOUT;
+			else
+				err = c.error;
+			break;
+		default:
+			break;
+	}
+
+	return err;
+}
+
+/*
+ * DST uses generic iteration approach for data crypto processing.
+ * Single block IO request is switched into array of scatterlists,
+ * which are submitted to the crypto processing iterator.
+ *
+ * Input and output iterator initialization are different, since
+ * in output case we can not encrypt data in-place and need a
+ * temporary storage, which is then being sent to the remote peer.
+ */
+static int dst_trans_iter_out(struct bio *bio, struct dst_crypto_engine *e,
+		int (* iterator) (struct dst_crypto_engine *e,
+				  struct scatterlist *dst,
+				  struct scatterlist *src))
+{
+	struct bio_vec *bv;
+	int err, i;
+
+	sg_init_table(e->src, bio->bi_vcnt);
+	sg_init_table(e->dst, bio->bi_vcnt);
+
+	bio_for_each_segment(bv, bio, i) {
+		sg_set_page(&e->src[i], bv->bv_page, bv->bv_len, bv->bv_offset);
+		sg_set_page(&e->dst[i], e->pages[i], bv->bv_len, bv->bv_offset);
+
+		err = iterator(e, &e->dst[i], &e->src[i]);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+static int dst_trans_iter_in(struct bio *bio, struct dst_crypto_engine *e,
+		int (* iterator) (struct dst_crypto_engine *e,
+				  struct scatterlist *dst,
+				  struct scatterlist *src))
+{
+	struct bio_vec *bv;
+	int err, i;
+
+	sg_init_table(e->src, bio->bi_vcnt);
+	sg_init_table(e->dst, bio->bi_vcnt);
+
+	bio_for_each_segment(bv, bio, i) {
+		sg_set_page(&e->src[i], bv->bv_page, bv->bv_len, bv->bv_offset);
+		sg_set_page(&e->dst[i], bv->bv_page, bv->bv_len, bv->bv_offset);
+
+		err = iterator(e, &e->dst[i], &e->src[i]);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+static int dst_crypt_iterator(struct dst_crypto_engine *e,
+		struct scatterlist *sg_dst, struct scatterlist *sg_src)
+{
+	struct ablkcipher_request *req = e->data;
+	u8 iv[32];
+
+	memset(iv, 0, sizeof(iv));
+
+	memcpy(iv, &e->iv, sizeof(e->iv));
+
+	return dst_crypto_process(req, sg_dst, sg_src, iv, e->enc, e->timeout);
+}
+
+static int dst_crypt(struct dst_crypto_engine *e, struct bio *bio)
+{
+	struct ablkcipher_request *req = e->data;
+
+	memset(req, 0, sizeof(struct ablkcipher_request));
+	ablkcipher_request_set_tfm(req, e->cipher);
+
+	if (e->enc)
+		return dst_trans_iter_out(bio, e, dst_crypt_iterator);
+	else
+		return dst_trans_iter_in(bio, e, dst_crypt_iterator);
+}
+
+static int dst_hash_iterator(struct dst_crypto_engine *e,
+		struct scatterlist *sg_dst, struct scatterlist *sg_src)
+{
+	return crypto_hash_update(e->data, sg_src, sg_src->length);
+}
+
+static int dst_hash(struct dst_crypto_engine *e, struct bio *bio, void *dst)
+{
+	struct hash_desc *desc = e->data;
+	int err;
+
+	desc->tfm = e->hash;
+	desc->flags = 0;
+
+	err = crypto_hash_init(desc);
+	if (err)
+		return err;
+
+	err = dst_trans_iter_in(bio, e, dst_hash_iterator);
+	if (err)
+		return err;
+
+	err = crypto_hash_final(desc, dst);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+/*
+ * Initialize/cleanup a crypto thread. The only thing it should
+ * do is to allocate a pool of pages as temporary storage.
+ * And to setup cipher and/or hash.
+ */
+static void *dst_crypto_thread_init(void *data)
+{
+	struct dst_node *n = data;
+	struct dst_crypto_engine *e;
+	int err = -ENOMEM;
+
+	e = kzalloc(sizeof(struct dst_crypto_engine), GFP_KERNEL);
+	if (!e)
+		goto err_out_exit;
+	e->src = kcalloc(2 * n->max_pages, sizeof(struct scatterlist),
+			GFP_KERNEL);
+	if (!e->src)
+		goto err_out_free;
+
+	e->dst = e->src + n->max_pages;
+
+	err = dst_crypto_engine_init(e, n);
+	if (err)
+		goto err_out_free_all;
+
+	return e;
+
+err_out_free_all:
+	kfree(e->src);
+err_out_free:
+	kfree(e);
+err_out_exit:
+	return ERR_PTR(err);
+}
+
+static void dst_crypto_thread_cleanup(void *private)
+{
+	struct dst_crypto_engine *e = private;
+
+	dst_crypto_engine_exit(e);
+	kfree(e->src);
+	kfree(e);
+}
+
+/*
+ * Initialize crypto engine for given node: store keys, create pool
+ * of threads, initialize each one.
+ *
+ * Each thread has unique ID, but 0 and 1 are reserved for receiving and accepting
+ * threads (if export node), so IDs could start from 2, but starting them
+ * from 10 allows easily understand what this thread is for.
+ */
+int dst_node_crypto_init(struct dst_node *n, struct dst_crypto_ctl *ctl)
+{
+	void *key = (ctl + 1);
+	int err = -ENOMEM, i;
+	char name[32];
+
+	if (ctl->hash_keysize) {
+		n->hash_key = kmalloc(ctl->hash_keysize, GFP_KERNEL);
+		if (!n->hash_key)
+			goto err_out_exit;
+		memcpy(n->hash_key, key, ctl->hash_keysize);
+	}
+
+	if (ctl->cipher_keysize) {
+		n->cipher_key = kmalloc(ctl->cipher_keysize, GFP_KERNEL);
+		if (!n->cipher_key)
+			goto err_out_free_hash;
+		memcpy(n->cipher_key, key, ctl->cipher_keysize);
+	}
+	memcpy(&n->crypto, ctl, sizeof(struct dst_crypto_ctl));
+
+	for (i=0; i<ctl->thread_num; ++i) {
+		snprintf(name, sizeof(name), "%s-crypto-%d", n->name, i);
+		/* Unique ids... */
+		err = thread_pool_add_worker(n->pool, name, i+10,
+			dst_crypto_thread_init, dst_crypto_thread_cleanup, n);
+		if (err)
+			goto err_out_free_threads;
+	}
+
+	return 0;
+
+err_out_free_threads:
+	while (--i >= 0)
+		thread_pool_del_worker_id(n->pool, i+10);
+
+	if (ctl->cipher_keysize)
+		kfree(n->cipher_key);
+	ctl->cipher_keysize = 0;
+err_out_free_hash:
+	if (ctl->hash_keysize)
+		kfree(n->hash_key);
+	ctl->hash_keysize = 0;
+err_out_exit:
+	return err;
+}
+
+void dst_node_crypto_exit(struct dst_node *n)
+{
+	struct dst_crypto_ctl *ctl = &n->crypto;
+
+	if (ctl->cipher_algo[0] || ctl->hash_algo[0]) {
+		kfree(n->hash_key);
+		kfree(n->cipher_key);
+	}
+}
+
+/*
+ * Thrad pool setup callback. Just stores a transaction in private data.
+ */
+static int dst_trans_crypto_setup(void *crypto_engine, void *trans)
+{
+	struct dst_crypto_engine *e = crypto_engine;
+
+	e->private = trans;
+	return 0;
+}
+
+#if 0
+static void dst_dump_bio(struct bio *bio)
+{
+	u8 *p;
+	struct bio_vec *bv;
+	int i;
+
+	bio_for_each_segment(bv, bio, i) {
+		dprintk("%s: %llu/%u: size: %u, offset: %u, data: ",
+				__func__, bio->bi_sector, bio->bi_size,
+				bv->bv_len, bv->bv_offset);
+
+		p = kmap(bv->bv_page) + bv->bv_offset;
+		for (i=0; i<bv->bv_len; ++i)
+			printk("%02x ", p[i]);
+		kunmap(bv->bv_page);
+		printk("\n");
+	}
+}
+#endif
+
+/*
+ * Encrypt/hash data and send it to the network.
+ */
+static int dst_crypto_process_sending(struct dst_crypto_engine *e,
+		struct bio *bio, u8 *hash)
+{
+	int err;
+
+	if (e->cipher) {
+		err = dst_crypt(e, bio);
+		if (err)
+			goto err_out_exit;
+	}
+
+	if (e->hash) {
+		err = dst_hash(e, bio, hash);
+		if (err)
+			goto err_out_exit;
+
+#ifdef CONFIG_DST_DEBUG
+		{
+			unsigned int i;
+
+			/* dst_dump_bio(bio); */
+
+			printk(KERN_DEBUG "%s: bio: %llu/%u, rw: %lu, hash: ",
+				__func__, (u64)bio->bi_sector,
+				bio->bi_size, bio_data_dir(bio));
+			for (i=0; i<crypto_hash_digestsize(e->hash); ++i)
+					printk("%02x ", hash[i]);
+			printk("\n");
+		}
+#endif
+	}
+
+	return 0;
+
+err_out_exit:
+	return err;
+}
+
+/*
+ * Check if received data is valid. Decipher if it is.
+ */
+static int dst_crypto_process_receiving(struct dst_crypto_engine *e,
+		struct bio *bio, u8 *hash, u8 *recv_hash)
+{
+	int err;
+
+	if (e->hash) {
+		int mismatch;
+
+		err = dst_hash(e, bio, hash);
+		if (err)
+			goto err_out_exit;
+
+		mismatch = !!memcmp(recv_hash, hash,
+				crypto_hash_digestsize(e->hash));
+#ifdef CONFIG_DST_DEBUG
+		/* dst_dump_bio(bio); */
+
+		printk(KERN_DEBUG "%s: bio: %llu/%u, rw: %lu, hash mismatch: %d",
+			__func__, (u64)bio->bi_sector, bio->bi_size,
+			bio_data_dir(bio), mismatch);
+		if (mismatch) {
+			unsigned int i;
+
+			printk(", recv/calc: ");
+			for (i=0; i<crypto_hash_digestsize(e->hash); ++i) {
+				printk("%02x/%02x ", recv_hash[i], hash[i]);
+			}
+		}
+		printk("\n");
+#endif
+		err = -1;
+		if (mismatch)
+			goto err_out_exit;
+	}
+
+	if (e->cipher) {
+		err = dst_crypt(e, bio);
+		if (err)
+			goto err_out_exit;
+	}
+
+	return 0;
+
+err_out_exit:
+	return err;
+}
+
+/*
+ * Thread pool callback to encrypt data and send it to the netowork.
+ */
+static int dst_trans_crypto_action(void *crypto_engine, void *schedule_data)
+{
+	struct dst_crypto_engine *e = crypto_engine;
+	struct dst_trans *t = schedule_data;
+	struct bio *bio = t->bio;
+	int err;
+
+	dprintk("%s: t: %p, gen: %llu, cipher: %p, hash: %p.\n",
+			__func__, t, t->gen, e->cipher, e->hash);
+
+	e->enc = t->enc;
+	e->iv = dst_gen_iv(t);
+
+	if (bio_data_dir(bio) == WRITE) {
+		err = dst_crypto_process_sending(e, bio, t->cmd.hash);
+		if (err)
+			goto err_out_exit;
+
+		if (e->hash) {
+			t->cmd.csize = crypto_hash_digestsize(e->hash);
+			t->cmd.size += t->cmd.csize;
+		}
+
+		return dst_trans_send(t);
+	} else {
+		u8 *hash = e->data + e->size/2;
+
+		err = dst_crypto_process_receiving(e, bio, hash, t->cmd.hash);
+		if (err)
+			goto err_out_exit;
+
+		dst_trans_remove(t);
+		dst_trans_put(t);
+	}
+
+	return 0;
+
+err_out_exit:
+	t->error = err;
+	dst_trans_put(t);
+	return err;
+}
+
+/*
+ * Schedule crypto processing for given transaction.
+ */
+int dst_trans_crypto(struct dst_trans *t)
+{
+	struct dst_node *n = t->n;
+	int err;
+
+	err = thread_pool_schedule(n->pool,
+		dst_trans_crypto_setup, dst_trans_crypto_action,
+		t, MAX_SCHEDULE_TIMEOUT);
+	if (err)
+		goto err_out_exit;
+
+	return 0;
+
+err_out_exit:
+	dst_trans_put(t);
+	return err;
+}
+
+/*
+ * Crypto machinery for the export node.
+ */
+static int dst_export_crypto_setup(void *crypto_engine, void *bio)
+{
+	struct dst_crypto_engine *e = crypto_engine;
+
+	e->private = bio;
+	return 0;
+}
+
+static int dst_export_crypto_action(void *crypto_engine, void *schedule_data)
+{
+	struct dst_crypto_engine *e = crypto_engine;
+	struct bio *bio = schedule_data;
+	struct dst_export_priv *p = bio->bi_private;
+	int err;
+
+	dprintk("%s: e: %p, data: %p, bio: %llu/%u, dir: %lu.\n", __func__,
+		e, e->data, (u64)bio->bi_sector, bio->bi_size, bio_data_dir(bio));
+
+	e->enc = (bio_data_dir(bio) == READ);
+	e->iv = p->cmd.id;
+
+	if (bio_data_dir(bio) == WRITE) {
+		u8 *hash = e->data + e->size/2;
+
+		err = dst_crypto_process_receiving(e, bio, hash, p->cmd.hash);
+		if (err)
+			goto err_out_exit;
+
+		generic_make_request(bio);
+	} else {
+		err = dst_crypto_process_sending(e, bio, p->cmd.hash);
+		if (err)
+			goto err_out_exit;
+
+		if (e->hash) {
+			p->cmd.csize = crypto_hash_digestsize(e->hash);
+			p->cmd.size += p->cmd.csize;
+		}
+
+		err = dst_export_send_bio(bio);
+	}
+	return 0;
+
+err_out_exit:
+	bio_put(bio);
+	return err;
+}
+
+int dst_export_crypto(struct dst_node *n, struct bio *bio)
+{
+	int err;
+
+	err = thread_pool_schedule(n->pool,
+		dst_export_crypto_setup, dst_export_crypto_action,
+		bio, MAX_SCHEDULE_TIMEOUT);
+	if (err)
+		goto err_out_exit;
+
+	return 0;
+
+err_out_exit:
+	bio_put(bio);
+	return err;
+}
diff --git a/drivers/block/dst/thread_pool.c b/drivers/block/dst/thread_pool.c
new file mode 100644
index 0000000..c35754d
--- /dev/null
+++ b/drivers/block/dst/thread_pool.c
@@ -0,0 +1,345 @@
+/*
+ * 2007+ Copyright (c) Evgeniy Polyakov <[email-masked]>
+ * 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/kernel.h>
+#include <linux/dst.h>
+#include <linux/kthread.h>
+#include <linux/slab.h>
+
+/*
+ * Thread pool abstraction allows to schedule a work to be performed
+ * on behalf of kernel thread. One does not operate with threads itself,
+ * instead user provides setup and cleanup callbacks for thread pool itself,
+ * and action and cleanup callbacks for each submitted work.
+ *
+ * Each worker has private data initialized at creation time and data,
+ * provided by user at scheduling time.
+ *
+ * When action is being performed, thread can not be used by other users,
+ * instead they will sleep until there is free thread to pick their work.
+ */
+struct thread_pool_worker
+{
+	struct list_head	worker_entry;
+
+	struct task_struct	*thread;
+
+	struct thread_pool	*pool;
+
+	int			error;
+	int			has_data;
+	int			need_exit;
+	unsigned int		id;
+
+	wait_queue_head_t	wait;
+
+	void			*private;
+	void			*schedule_data;
+
+	int			(* action)(void *private, void *schedule_data);
+	void			(* cleanup)(void *private);
+};
+
+static void thread_pool_exit_worker(struct thread_pool_worker *w)
+{
+	kthread_stop(w->thread);
+
+	w->cleanup(w->private);
+	kfree(w);
+}
+
+/*
+ * Called to mark thread as ready and allow users to schedule new work.
+ */
+static void thread_pool_worker_make_ready(struct thread_pool_worker *w)
+{
+	struct thread_pool *p = w->pool;
+
+	mutex_lock(&p->thread_lock);
+
+	if (!w->need_exit) {
+		list_move_tail(&w->worker_entry, &p->ready_list);
+		w->has_data = 0;
+		mutex_unlock(&p->thread_lock);
+
+		wake_up(&p->wait);
+	} else {
+		p->thread_num--;
+		list_del(&w->worker_entry);
+		mutex_unlock(&p->thread_lock);
+
+		thread_pool_exit_worker(w);
+	}
+}
+
+/*
+ * Thread action loop: waits until there is new work.
+ */
+static int thread_pool_worker_func(void *data)
+{
+	struct thread_pool_worker *w = data;
+
+	while (!kthread_should_stop()) {
+		wait_event_interruptible(w->wait,
+			kthread_should_stop() || w->has_data);
+
+		if (kthread_should_stop())
+			break;
+
+		if (!w->has_data)
+			continue;
+
+		w->action(w->private, w->schedule_data);
+		thread_pool_worker_make_ready(w);
+	}
+
+	return 0;
+}
+
+/*
+ * Remove single worker without specifying which one.
+ */
+void thread_pool_del_worker(struct thread_pool *p)
+{
+	struct thread_pool_worker *w = NULL;
+
+	while (!w) {
+		wait_event(p->wait, !list_empty(&p->ready_list) || !p->thread_num);
+
+		dprintk("%s: locking list_empty: %d, thread_num: %d.\n",
+				__func__, list_empty(&p->ready_list), p->thread_num);
+
+		mutex_lock(&p->thread_lock);
+		if (!list_empty(&p->ready_list)) {
+			w = list_first_entry(&p->ready_list,
+					struct thread_pool_worker,
+					worker_entry);
+
+			dprintk("%s: deleting w: %p, thread_num: %d, list: %p [%p.%p].\n",
+					__func__, w, p->thread_num, &p->ready_list,
+					p->ready_list.prev, p->ready_list.next);
+
+			p->thread_num--;
+			list_del(&w->worker_entry);
+		}
+		mutex_unlock(&p->thread_lock);
+	}
+
+	if (w)
+		thread_pool_exit_worker(w);
+	dprintk("%s: deleted w: %p, thread_num: %d.\n",
+			__func__, w, p->thread_num);
+}
+
+/*
+ * Remove a worker with given ID.
+ */
+void thread_pool_del_worker_id(struct thread_pool *p, unsigned int id)
+{
+	struct thread_pool_worker *w;
+	int found = 0;
+
+	mutex_lock(&p->thread_lock);
+	list_for_each_entry(w, &p->ready_list, worker_entry) {
+		if (w->id == id) {
+			found = 1;
+			p->thread_num--;
+			list_del(&w->worker_entry);
+			break;
+		}
+	}
+
+	if (!found) {
+		list_for_each_entry(w, &p->active_list, worker_entry) {
+			if (w->id == id) {
+				w->need_exit = 1;
+				break;
+			}
+		}
+	}
+	mutex_unlock(&p->thread_lock);
+
+	if (found)
+		thread_pool_exit_worker(w);
+}
+
+/*
+ * Add new worker thread with given parameters.
+ * If initialization callback fails, return error.
+ */
+int thread_pool_add_worker(struct thread_pool *p,
+		char *name,
+		unsigned int id,
+		void *(* init)(void *private),
+		void (* cleanup)(void *private),
+		void *private)
+{
+	struct thread_pool_worker *w;
+	int err = -ENOMEM;
+
+	w = kzalloc(sizeof(struct thread_pool_worker), GFP_KERNEL);
+	if (!w)
+		goto err_out_exit;
+
+	w->pool = p;
+	init_waitqueue_head(&w->wait);
+	w->cleanup = cleanup;
+	w->id = id;
+
+	w->thread = kthread_run(thread_pool_worker_func, w, "%s", name);
+	if (IS_ERR(w->thread)) {
+		err = PTR_ERR(w->thread);
+		goto err_out_free;
+	}
+
+	w->private = init(private);
+	if (IS_ERR(w->private)) {
+		err = PTR_ERR(w->private);
+		goto err_out_stop_thread;
+	}
+
+	mutex_lock(&p->thread_lock);
+	list_add_tail(&w->worker_entry, &p->ready_list);
+	p->thread_num++;
+	mutex_unlock(&p->thread_lock);
+
+	return 0;
+
+err_out_stop_thread:
+	kthread_stop(w->thread);
+err_out_free:
+	kfree(w);
+err_out_exit:
+	return err;
+}
+
+/*
+ * Destroy the whole pool.
+ */
+void thread_pool_destroy(struct thread_pool *p)
+{
+	while (p->thread_num) {
+		dprintk("%s: num: %d.\n", __func__, p->thread_num);
+		thread_pool_del_worker(p);
+	}
+
+	kfree(p);
+}
+
+/*
+ * Create a pool with given number of threads.
+ * They will have sequential IDs started from zero.
+ */
+struct thread_pool *thread_pool_create(int num, char *name,
+		void *(* init)(void *private),
+		void (* cleanup)(void *private),
+		void *private)
+{
+	struct thread_pool_worker *w, *tmp;
+	struct thread_pool *p;
+	int err = -ENOMEM;
+	int i;
+
+	p = kzalloc(sizeof(struct thread_pool), GFP_KERNEL);
+	if (!p)
+		goto err_out_exit;
+
+	init_waitqueue_head(&p->wait);
+	mutex_init(&p->thread_lock);
+	INIT_LIST_HEAD(&p->ready_list);
+	INIT_LIST_HEAD(&p->active_list);
+	p->thread_num = 0;
+
+	for (i=0; i<num; ++i) {
+		err = thread_pool_add_worker(p, name, i, init,
+				cleanup, private);
+		if (err)
+			goto err_out_free_all;
+	}
+
+	return p;
+
+err_out_free_all:
+	list_for_each_entry_safe(w, tmp, &p->ready_list, worker_entry) {
+		list_del(&w->worker_entry);
+		thread_pool_exit_worker(w);
+	}
+	kfree(p);
+err_out_exit:
+	return ERR_PTR(err);
+}
+
+/*
+ * Schedule execution of the action on a given thread,
+ * provided ID pointer has to match previously stored
+ * private data.
+ */
+int thread_pool_schedule_private(struct thread_pool *p,
+		int (* setup)(void *private, void *data),
+		int (* action)(void *private, void *data),
+		void *data, long timeout, void *id)
+{
+	struct thread_pool_worker *w, *tmp, *worker = NULL;
+	int err = 0;
+
+	while (!worker && !err) {
+		timeout = wait_event_interruptible_timeout(p->wait,
+				!list_empty(&p->ready_list),
+				timeout);
+
+		if (!timeout) {
+			err = -ETIMEDOUT;
+			break;
+		}
+
+		worker = NULL;
+		mutex_lock(&p->thread_lock);
+		list_for_each_entry_safe(w, tmp, &p->ready_list, worker_entry) {
+			if (id && id != w->private)
+				continue;
+
+			worker = w;
+
+			list_move_tail(&w->worker_entry, &p->active_list);
+
+			err = setup(w->private, data);
+			if (!err) {
+				w->schedule_data = data;
+				w->action = action;
+				w->has_data = 1;
+				wake_up(&w->wait);
+			} else {
+				list_move_tail(&w->worker_entry, &p->ready_list);
+			}
+
+			break;
+		}
+		mutex_unlock(&p->thread_lock);
+	}
+
+	return err;
+}
+
+/*
+ * Schedule execution on arbitrary thread from the pool.
+ */
+int thread_pool_schedule(struct thread_pool *p,
+		int (* setup)(void *private, void *data),
+		int (* action)(void *private, void *data),
+		void *data, long timeout)
+{
+	return thread_pool_schedule_private(p, setup,
+			action, data, timeout, NULL);
+}