Message-ID: <20221209142331.26395-12-sergei.shtepa@veeam.com>
Date:   Fri, 9 Dec 2022 15:23:21 +0100
From:   Sergei Shtepa <sergei.shtepa@...am.com>
To:     <axboe@...nel.dk>, <corbet@....net>
CC:     <linux-block@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Sergei Shtepa <sergei.shtepa@...am.com>
Subject: [PATCH v2 11/21] block, blksnap: minimum data storage unit of the original block device

The struct chunk describes the minimum data storage unit of the original
block device. Functions for working with these minimal blocks implement
algorithms for reading and writing blocks.

Signed-off-by: Sergei Shtepa <sergei.shtepa@...am.com>
---
 drivers/block/blksnap/chunk.c | 345 ++++++++++++++++++++++++++++++++++
 drivers/block/blksnap/chunk.h | 139 ++++++++++++++
 2 files changed, 484 insertions(+)
 create mode 100644 drivers/block/blksnap/chunk.c
 create mode 100644 drivers/block/blksnap/chunk.h

diff --git a/drivers/block/blksnap/chunk.c b/drivers/block/blksnap/chunk.c
new file mode 100644
index 000000000000..563a6b1612d3
--- /dev/null
+++ b/drivers/block/blksnap/chunk.c
@@ -0,0 +1,345 @@
+// SPDX-License-Identifier: GPL-2.0
+#define pr_fmt(fmt) KBUILD_MODNAME "-chunk: " fmt
+
+#include <linux/slab.h>
+#include <linux/dm-io.h>
+#include <linux/sched/mm.h>
+#include "params.h"
+#include "chunk.h"
+#include "diff_io.h"
+#include "diff_buffer.h"
+#include "diff_area.h"
+#include "diff_storage.h"
+
+void chunk_diff_buffer_release(struct chunk *chunk)
+{
+	if (unlikely(!chunk->diff_buffer))
+		return;
+
+	chunk_state_unset(chunk, CHUNK_ST_BUFFER_READY);
+	diff_buffer_release(chunk->diff_area, chunk->diff_buffer);
+	chunk->diff_buffer = NULL;
+}
+
+void chunk_store_failed(struct chunk *chunk, int error)
+{
+	struct diff_area *diff_area = chunk->diff_area;
+
+	chunk_state_set(chunk, CHUNK_ST_FAILED);
+	chunk_diff_buffer_release(chunk);
+	diff_storage_free_region(chunk->diff_region);
+	chunk->diff_region = NULL;
+
+	up(&chunk->lock);
+	if (error)
+		diff_area_set_corrupted(diff_area, error);
+};
+
+int chunk_schedule_storing(struct chunk *chunk, bool is_nowait)
+{
+	struct diff_area *diff_area = chunk->diff_area;
+
+	if (WARN(!list_is_first(&chunk->cache_link, &chunk->cache_link),
+		 "The chunk already in the cache"))
+		return -EINVAL;
+
+	if (!chunk->diff_region) {
+		struct diff_region *diff_region;
+
+		diff_region = diff_storage_new_region(
+			diff_area->diff_storage,
+			diff_area_chunk_sectors(diff_area));
+		if (IS_ERR(diff_region)) {
+			pr_debug("Cannot get store for chunk #%ld\n",
+				 chunk->number);
+			return PTR_ERR(diff_region);
+		}
+
+		chunk->diff_region = diff_region;
+	}
+
+	return chunk_async_store_diff(chunk, is_nowait);
+}
+
+void chunk_schedule_caching(struct chunk *chunk)
+{
+	int in_cache_count = 0;
+	struct diff_area *diff_area = chunk->diff_area;
+
+	might_sleep();
+
+	spin_lock(&diff_area->caches_lock);
+
+	/*
+	 * The locked chunk cannot be in the cache.
+	 * If the check reveals that the chunk is in the cache, then something
+	 * is wrong in the algorithm.
+	 */
+	if (WARN(!list_is_first(&chunk->cache_link, &chunk->cache_link),
+		 "The chunk already in the cache")) {
+		spin_unlock(&diff_area->caches_lock);
+
+		chunk_store_failed(chunk, 0);
+		return;
+	}
+
+	if (chunk_state_check(chunk, CHUNK_ST_DIRTY)) {
+		list_add_tail(&chunk->cache_link,
+			      &diff_area->write_cache_queue);
+		in_cache_count =
+			atomic_inc_return(&diff_area->write_cache_count);
+	} else {
+		list_add_tail(&chunk->cache_link, &diff_area->read_cache_queue);
+		in_cache_count =
+			atomic_inc_return(&diff_area->read_cache_count);
+	}
+	spin_unlock(&diff_area->caches_lock);
+
+	up(&chunk->lock);
+
+	/* Initiate the cache clearing process */
+	if ((in_cache_count > chunk_maximum_in_cache) &&
+	    !diff_area_is_corrupted(diff_area))
+		queue_work(system_wq, &diff_area->cache_release_work);
+}
+
+static void chunk_notify_load(void *ctx)
+{
+	struct chunk *chunk = ctx;
+	int error = chunk->diff_io->error;
+
+	diff_io_free(chunk->diff_io);
+	chunk->diff_io = NULL;
+
+	might_sleep();
+
+	if (unlikely(error)) {
+		chunk_store_failed(chunk, error);
+		goto out;
+	}
+
+	if (unlikely(chunk_state_check(chunk, CHUNK_ST_FAILED))) {
+		pr_err("Chunk in a failed state\n");
+		up(&chunk->lock);
+		goto out;
+	}
+
+	if (chunk_state_check(chunk, CHUNK_ST_LOADING)) {
+		int ret;
+		unsigned int current_flag;
+
+		chunk_state_unset(chunk, CHUNK_ST_LOADING);
+		chunk_state_set(chunk, CHUNK_ST_BUFFER_READY);
+
+		current_flag = memalloc_noio_save();
+		ret = chunk_schedule_storing(chunk, false);
+		memalloc_noio_restore(current_flag);
+		if (ret)
+			chunk_store_failed(chunk, ret);
+		goto out;
+	}
+
+	pr_err("invalid chunk state 0x%x\n", atomic_read(&chunk->state));
+	up(&chunk->lock);
+out:
+	atomic_dec(&chunk->diff_area->pending_io_count);
+}
+
+static void chunk_notify_store(void *ctx)
+{
+	struct chunk *chunk = ctx;
+	int error = chunk->diff_io->error;
+
+	diff_io_free(chunk->diff_io);
+	chunk->diff_io = NULL;
+
+	might_sleep();
+
+	if (unlikely(error)) {
+		chunk_store_failed(chunk, error);
+		goto out;
+	}
+
+	if (unlikely(chunk_state_check(chunk, CHUNK_ST_FAILED))) {
+		pr_err("Chunk in a failed state\n");
+		chunk_store_failed(chunk, 0);
+		goto out;
+	}
+	if (chunk_state_check(chunk, CHUNK_ST_STORING)) {
+		chunk_state_unset(chunk, CHUNK_ST_STORING);
+		chunk_state_set(chunk, CHUNK_ST_STORE_READY);
+
+		if (chunk_state_check(chunk, CHUNK_ST_DIRTY)) {
+			/*
+			 * The chunk marked "dirty" was stored in the difference
+			 * storage. Now it is processed in the same way as any
+			 * other stored chunks.
+			 * Therefore, the "dirty" mark can be removed.
+			 */
+			chunk_state_unset(chunk, CHUNK_ST_DIRTY);
+			chunk_diff_buffer_release(chunk);
+		} else {
+			unsigned int current_flag;
+
+			current_flag = memalloc_noio_save();
+			chunk_schedule_caching(chunk);
+			memalloc_noio_restore(current_flag);
+			goto out;
+		}
+	} else
+		pr_err("invalid chunk state 0x%x\n", atomic_read(&chunk->state));
+	up(&chunk->lock);
+out:
+	atomic_dec(&chunk->diff_area->pending_io_count);
+}
+
+struct chunk *chunk_alloc(struct diff_area *diff_area, unsigned long number)
+{
+	struct chunk *chunk;
+
+	chunk = kzalloc(sizeof(struct chunk), GFP_KERNEL);
+	if (!chunk)
+		return NULL;
+
+	INIT_LIST_HEAD(&chunk->cache_link);
+	sema_init(&chunk->lock, 1);
+	chunk->diff_area = diff_area;
+	chunk->number = number;
+	atomic_set(&chunk->state, 0);
+
+	return chunk;
+}
+
+void chunk_free(struct chunk *chunk)
+{
+	if (unlikely(!chunk))
+		return;
+
+	down(&chunk->lock);
+	chunk_diff_buffer_release(chunk);
+	diff_storage_free_region(chunk->diff_region);
+	chunk_state_set(chunk, CHUNK_ST_FAILED);
+	up(&chunk->lock);
+
+	kfree(chunk);
+}
+
+/*
+ * Starts asynchronous storing of a chunk to the  difference storage.
+ */
+int chunk_async_store_diff(struct chunk *chunk, bool is_nowait)
+{
+	int ret;
+	struct diff_io *diff_io;
+	struct diff_region *region = chunk->diff_region;
+
+	if (WARN(!list_is_first(&chunk->cache_link, &chunk->cache_link),
+		 "The chunk already in the cache"))
+		return -EINVAL;
+
+	diff_io = diff_io_new_async_write(chunk_notify_store, chunk, is_nowait);
+	if (unlikely(!diff_io)) {
+		if (is_nowait)
+			return -EAGAIN;
+		else
+			return -ENOMEM;
+	}
+
+	WARN_ON(chunk->diff_io);
+	chunk->diff_io = diff_io;
+	chunk_state_set(chunk, CHUNK_ST_STORING);
+	atomic_inc(&chunk->diff_area->pending_io_count);
+
+	ret = diff_io_do(chunk->diff_io, region, chunk->diff_buffer, is_nowait);
+	if (ret) {
+		atomic_dec(&chunk->diff_area->pending_io_count);
+		diff_io_free(chunk->diff_io);
+		chunk->diff_io = NULL;
+	}
+
+	return ret;
+}
+
+/*
+ * Starts asynchronous loading of a chunk from the original block device.
+ */
+int chunk_async_load_orig(struct chunk *chunk, const bool is_nowait)
+{
+	int ret;
+	struct diff_io *diff_io;
+	struct diff_region region = {
+		.bdev = chunk->diff_area->orig_bdev,
+		.sector = (sector_t)(chunk->number) *
+			  diff_area_chunk_sectors(chunk->diff_area),
+		.count = chunk->sector_count,
+	};
+
+	diff_io = diff_io_new_async_read(chunk_notify_load, chunk, is_nowait);
+	if (unlikely(!diff_io)) {
+		if (is_nowait)
+			return -EAGAIN;
+		else
+			return -ENOMEM;
+	}
+
+	WARN_ON(chunk->diff_io);
+	chunk->diff_io = diff_io;
+	chunk_state_set(chunk, CHUNK_ST_LOADING);
+	atomic_inc(&chunk->diff_area->pending_io_count);
+
+	ret = diff_io_do(chunk->diff_io, &region, chunk->diff_buffer, is_nowait);
+	if (ret) {
+		atomic_dec(&chunk->diff_area->pending_io_count);
+		diff_io_free(chunk->diff_io);
+		chunk->diff_io = NULL;
+	}
+	return ret;
+}
+
+/*
+ * Performs synchronous loading of a chunk from the original block device.
+ */
+int chunk_load_orig(struct chunk *chunk)
+{
+	int ret;
+	struct diff_io *diff_io;
+	struct diff_region region = {
+		.bdev = chunk->diff_area->orig_bdev,
+		.sector = (sector_t)(chunk->number) *
+			  diff_area_chunk_sectors(chunk->diff_area),
+		.count = chunk->sector_count,
+	};
+
+	diff_io = diff_io_new_sync_read();
+	if (unlikely(!diff_io))
+		return -ENOMEM;
+
+	ret = diff_io_do(diff_io, &region, chunk->diff_buffer, false);
+	if (!ret)
+		ret = diff_io->error;
+
+	diff_io_free(diff_io);
+	return ret;
+}
+
+/*
+ * Performs synchronous loading of a chunk from the difference storage.
+ */
+int chunk_load_diff(struct chunk *chunk)
+{
+	int ret;
+	struct diff_io *diff_io;
+	struct diff_region *region = chunk->diff_region;
+
+	diff_io = diff_io_new_sync_read();
+	if (unlikely(!diff_io))
+		return -ENOMEM;
+
+	ret = diff_io_do(diff_io, region, chunk->diff_buffer, false);
+	if (!ret)
+		ret = diff_io->error;
+
+	diff_io_free(diff_io);
+
+	return ret;
+}
diff --git a/drivers/block/blksnap/chunk.h b/drivers/block/blksnap/chunk.h
new file mode 100644
index 000000000000..6f2350930095
--- /dev/null
+++ b/drivers/block/blksnap/chunk.h
@@ -0,0 +1,139 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __BLK_SNAP_CHUNK_H
+#define __BLK_SNAP_CHUNK_H
+
+#include <linux/blk_types.h>
+#include <linux/blkdev.h>
+#include <linux/rwsem.h>
+#include <linux/atomic.h>
+
+struct diff_area;
+struct diff_region;
+struct diff_io;
+
+/**
+ * enum chunk_st - Possible states for a chunk.
+ *
+ * @CHUNK_ST_FAILED:
+ *	An error occurred while processing the chunk data.
+ * @CHUNK_ST_DIRTY:
+ *	The chunk is in the dirty state. The chunk is marked dirty in case
+ *	there was a write operation to the snapshot image.
+ *	The flag is removed when the data of the chunk is stored in the
+ *	difference storage.
+ * @CHUNK_ST_BUFFER_READY:
+ *	The data of the chunk is ready to be read from the RAM buffer.
+ *	The flag is removed when a chunk is removed from the cache and its
+ *	buffer is released.
+ * @CHUNK_ST_STORE_READY:
+ *	The data of the chunk has been written to the difference storage.
+ *	The flag cannot be removed.
+ * @CHUNK_ST_LOADING:
+ *	The data is being read from the original block device.
+ *	The flag is replaced with the CHUNK_ST_BUFFER_READY flag.
+ * @CHUNK_ST_STORING:
+ *	The data is being saved to the difference storage.
+ *	The flag is replaced with the CHUNK_ST_STORE_READY flag.
+ *
+ * Chunks life circle.
+ * Copy-on-write when writing to original:
+ *	0 -> LOADING -> BUFFER_READY -> BUFFER_READY | STORING ->
+ *	BUFFER_READY | STORE_READY -> STORE_READY
+ * Write to snapshot image:
+ *	0 -> LOADING -> BUFFER_READY | DIRTY -> DIRTY | STORING ->
+ *	BUFFER_READY | STORE_READY -> STORE_READY
+ */
+enum chunk_st {
+	CHUNK_ST_FAILED = (1 << 0),
+	CHUNK_ST_DIRTY = (1 << 1),
+	CHUNK_ST_BUFFER_READY = (1 << 2),
+	CHUNK_ST_STORE_READY = (1 << 3),
+	CHUNK_ST_LOADING = (1 << 4),
+	CHUNK_ST_STORING = (1 << 5),
+};
+
+/**
+ * struct chunk - Minimum data storage unit.
+ *
+ * @cache_link:
+ *	The list header allows to create caches of chunks.
+ * @diff_area:
+ *	Pointer to the difference area - the storage of changes for a specific device.
+ * @number:
+ *	Sequential number of the chunk.
+ * @sector_count:
+ *	Number of sectors in the current chunk. This is especially true
+ *	for the	last chunk.
+ * @lock:
+ *	Binary semaphore. Syncs access to the chunks fields: state,
+ *	diff_buffer, diff_region and diff_io.
+ * @state:
+ *	Defines the state of a chunk. May contain CHUNK_ST_* bits.
+ * @diff_buffer:
+ *	Pointer to &struct diff_buffer. Describes a buffer in the memory
+ *	for storing the chunk data.
+ * @diff_region:
+ *	Pointer to &struct diff_region. Describes a copy of the chunk data
+ *	on the difference storage.
+ * @diff_io:
+ *	Provides I/O operations for a chunk.
+ *
+ * This structure describes the block of data that the module operates
+ * with when executing the copy-on-write algorithm and when performing I/O
+ * to snapshot images.
+ *
+ * If the data of the chunk has been changed or has just been read, then
+ * the chunk gets into cache.
+ *
+ * The semaphore is blocked for writing if there is no actual data in the
+ * buffer, since a block of data is being read from the original device or
+ * from a diff storage. If data is being read from or written to the
+ * diff_buffer, the semaphore must be locked.
+ */
+struct chunk {
+	struct list_head cache_link;
+	struct diff_area *diff_area;
+
+	unsigned long number;
+	sector_t sector_count;
+
+	struct semaphore lock;
+
+	atomic_t state;
+	struct diff_buffer *diff_buffer;
+	struct diff_region *diff_region;
+	struct diff_io *diff_io;
+};
+
+static inline void chunk_state_set(struct chunk *chunk, int st)
+{
+	atomic_or(st, &chunk->state);
+};
+
+static inline void chunk_state_unset(struct chunk *chunk, int st)
+{
+	atomic_and(~st, &chunk->state);
+};
+
+static inline bool chunk_state_check(struct chunk *chunk, int st)
+{
+	return !!(atomic_read(&chunk->state) & st);
+};
+
+struct chunk *chunk_alloc(struct diff_area *diff_area, unsigned long number);
+void chunk_free(struct chunk *chunk);
+
+int chunk_schedule_storing(struct chunk *chunk, bool is_nowait);
+void chunk_diff_buffer_release(struct chunk *chunk);
+void chunk_store_failed(struct chunk *chunk, int error);
+
+void chunk_schedule_caching(struct chunk *chunk);
+
+/* Asynchronous operations are used to implement the COW algorithm. */
+int chunk_async_store_diff(struct chunk *chunk, bool is_nowait);
+int chunk_async_load_orig(struct chunk *chunk, const bool is_nowait);
+
+/* Synchronous operations are used to implement reading and writing to the snapshot image. */
+int chunk_load_orig(struct chunk *chunk);
+int chunk_load_diff(struct chunk *chunk);
+#endif /* __BLK_SNAP_CHUNK_H */
-- 
2.20.1

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