[PATCH 12/20] block, blksnap: storage for storing difference blocks

Sergei Shtepa
2022-06-13T18:54:21Z

Provides management of regions of block devices available for storing
difference blocks of a snapshot. Contains lists of free and already
occupied regions.

Signed-off-by: Sergei Shtepa <sergei.shtepa@veeam.com>
---
drivers/block/blksnap/diff_storage.c | 316 +++++++++++++++++++++++++++
drivers/block/blksnap/diff_storage.h | 94 ++++++++
2 files changed, 410 insertions(+)
create mode 100644 drivers/block/blksnap/diff_storage.c
create mode 100644 drivers/block/blksnap/diff_storage.h

diff --git a/drivers/block/blksnap/diff_storage.c b/drivers/block/blksnap/diff_storage.c
new file mode 100644
index 000000000000..7138ad53606d
--- /dev/null
+++ b/drivers/block/blksnap/diff_storage.c
@@ -0,0 +1,316 @@
+// SPDX-License-Identifier: GPL-2.0
+#define pr_fmt(fmt) KBUILD_MODNAME "-diff-storage: " fmt
+#include <linux/slab.h>
+#include <linux/sched/mm.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/blk_snap.h>
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+#include "memory_checker.h"
+#endif
+#include "params.h"
+#include "chunk.h"
+#include "diff_io.h"
+#include "diff_buffer.h"
+#include "diff_storage.h"
+
+/**
+ * struct storage_bdev - Information about the opened block device.
+ */
+struct storage_bdev {
+ struct list_head link;
+ dev_t dev_id;
+ struct block_device *bdev;
+};
+
+/**
+ * struct storage_block - A storage unit reserved for storing differences.
+ *
+ */
+struct storage_block {
+ struct list_head link;
+ struct block_device *bdev;
+ sector_t sector;
+ sector_t count;
+ sector_t used;
+};
+
+static inline void diff_storage_event_low(struct diff_storage *diff_storage)
+{
+ struct blk_snap_event_low_free_space data = {
+ .requested_nr_sect = diff_storage_minimum,
+ };
+
+ diff_storage->requested += data.requested_nr_sect;
+ pr_debug(
+ "Diff storage low free space. Portion: %llu sectors, requested: %llu\n",
+ data.requested_nr_sect, diff_storage->requested);
+ event_gen(&diff_storage->event_queue, GFP_NOIO,
+ blk_snap_event_code_low_free_space, &data, sizeof(data));
+}
+
+struct diff_storage *diff_storage_new(void)
+{
+ struct diff_storage *diff_storage;
+
+ diff_storage = kzalloc(sizeof(struct diff_storage), GFP_KERNEL);
+ if (!diff_storage)
+ return NULL;
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+ memory_object_inc(memory_object_diff_storage);
+#endif
+ kref_init(&diff_storage->kref);
+ spin_lock_init(&diff_storage->lock);
+ INIT_LIST_HEAD(&diff_storage->storage_bdevs);
+ INIT_LIST_HEAD(&diff_storage->empty_blocks);
+ INIT_LIST_HEAD(&diff_storage->filled_blocks);
+
+ event_queue_init(&diff_storage->event_queue);
+ diff_storage_event_low(diff_storage);
+
+ return diff_storage;
+}
+
+static inline struct storage_block *
+first_empty_storage_block(struct diff_storage *diff_storage)
+{
+ return list_first_entry_or_null(&diff_storage->empty_blocks,
+ struct storage_block, link);
+};
+
+static inline struct storage_block *
+first_filled_storage_block(struct diff_storage *diff_storage)
+{
+ return list_first_entry_or_null(&diff_storage->filled_blocks,
+ struct storage_block, link);
+};
+
+static inline struct storage_bdev *
+first_storage_bdev(struct diff_storage *diff_storage)
+{
+ return list_first_entry_or_null(&diff_storage->storage_bdevs,
+ struct storage_bdev, link);
+};
+
+void diff_storage_free(struct kref *kref)
+{
+ struct diff_storage *diff_storage =
+ container_of(kref, struct diff_storage, kref);
+ struct storage_block *blk;
+ struct storage_bdev *storage_bdev;
+
+ while ((blk = first_empty_storage_block(diff_storage))) {
+ list_del(&blk->link);
+ kfree(blk);
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+ memory_object_dec(memory_object_storage_block);
+#endif
+ }
+
+ while ((blk = first_filled_storage_block(diff_storage))) {
+ list_del(&blk->link);
+ kfree(blk);
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+ memory_object_dec(memory_object_storage_block);
+#endif
+ }
+
+ while ((storage_bdev = first_storage_bdev(diff_storage))) {
+ blkdev_put(storage_bdev->bdev, FMODE_READ | FMODE_WRITE);
+ list_del(&storage_bdev->link);
+ kfree(storage_bdev);
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+ memory_object_dec(memory_object_storage_bdev);
+#endif
+ }
+ event_queue_done(&diff_storage->event_queue);
+
+ kfree(diff_storage);
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+ memory_object_dec(memory_object_diff_storage);
+#endif
+}
+
+struct block_device *diff_storage_bdev_by_id(struct diff_storage *diff_storage,
+ dev_t dev_id)
+{
+ struct block_device *bdev = NULL;
+ struct storage_bdev *storage_bdev;
+
+ spin_lock(&diff_storage->lock);
+ list_for_each_entry(storage_bdev, &diff_storage->storage_bdevs, link) {
+ if (storage_bdev->dev_id == dev_id) {
+ bdev = storage_bdev->bdev;
+ break;
+ }
+ }
+ spin_unlock(&diff_storage->lock);
+
+ return bdev;
+}
+
+static inline struct block_device *
+diff_storage_add_storage_bdev(struct diff_storage *diff_storage, dev_t dev_id)
+{
+ struct block_device *bdev;
+ struct storage_bdev *storage_bdev;
+
+ bdev = blkdev_get_by_dev(dev_id, FMODE_READ | FMODE_WRITE, NULL);
+ if (IS_ERR(bdev)) {
+ pr_err("Failed to open device. errno=%d\n",
+ abs((int)PTR_ERR(bdev)));
+ return bdev;
+ }
+
+ storage_bdev = kzalloc(sizeof(struct storage_bdev), GFP_KERNEL);
+ if (!storage_bdev) {
+ blkdev_put(bdev, FMODE_READ | FMODE_WRITE);
+ return ERR_PTR(-ENOMEM);
+ }
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+ memory_object_inc(memory_object_storage_bdev);
+#endif
+ storage_bdev->bdev = bdev;
+ storage_bdev->dev_id = dev_id;
+ INIT_LIST_HEAD(&storage_bdev->link);
+
+ spin_lock(&diff_storage->lock);
+ list_add_tail(&storage_bdev->link, &diff_storage->storage_bdevs);
+ spin_unlock(&diff_storage->lock);
+
+ return bdev;
+}
+
+static inline int diff_storage_add_range(struct diff_storage *diff_storage,
+ struct block_device *bdev,
+ sector_t sector, sector_t count)
+{
+ struct storage_block *storage_block;
+
+ pr_debug("Add range to diff storage: [%u:%u] %llu:%llu\n",
+ MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev), sector, count);
+
+ storage_block = kzalloc(sizeof(struct storage_block), GFP_KERNEL);
+ if (!storage_block)
+ return -ENOMEM;
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+ memory_object_inc(memory_object_storage_block);
+#endif
+ INIT_LIST_HEAD(&storage_block->link);
+ storage_block->bdev = bdev;
+ storage_block->sector = sector;
+ storage_block->count = count;
+
+ spin_lock(&diff_storage->lock);
+ list_add_tail(&storage_block->link, &diff_storage->empty_blocks);
+ diff_storage->capacity += count;
+ spin_unlock(&diff_storage->lock);
+
+ return 0;
+}
+
+int diff_storage_append_block(struct diff_storage *diff_storage, dev_t dev_id,
+ struct big_buffer *ranges,
+ unsigned int range_count)
+{
+ int ret;
+ int inx;
+ struct block_device *bdev;
+ struct blk_snap_block_range *range;
+
+ pr_debug("Append %u blocks\n", range_count);
+
+ bdev = diff_storage_bdev_by_id(diff_storage, dev_id);
+ if (!bdev) {
+ bdev = diff_storage_add_storage_bdev(diff_storage, dev_id);
+ if (IS_ERR(bdev))
+ return PTR_ERR(bdev);
+ }
+
+ for (inx = 0; inx < range_count; inx++) {
+ range = big_buffer_get_element(
+ ranges, inx, sizeof(struct blk_snap_block_range));
+ if (unlikely(!range))
+ return -EINVAL;
+
+ ret = diff_storage_add_range(diff_storage, bdev,
+ range->sector_offset,
+ range->sector_count);
+ if (unlikely(ret))
+ return ret;
+ }
+
+ if (atomic_read(&diff_storage->low_space_flag) &&
+ (diff_storage->capacity >= diff_storage->requested))
+ atomic_set(&diff_storage->low_space_flag, 0);
+
+ return 0;
+}
+
+struct diff_region *diff_storage_new_region(struct diff_storage *diff_storage,
+ sector_t count)
+{
+ int ret = 0;
+ struct diff_region *diff_region;
+ sector_t sectors_left;
+
+ if (atomic_read(&diff_storage->overflow_flag))
+ return ERR_PTR(-ENOSPC);
+
+ diff_region = kzalloc(sizeof(struct diff_region), GFP_NOIO);
+ if (!diff_region)
+ return ERR_PTR(-ENOMEM);
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+ memory_object_inc(memory_object_diff_region);
+#endif
+ spin_lock(&diff_storage->lock);
+ do {
+ struct storage_block *storage_block;
+ sector_t available;
+
+ storage_block = first_empty_storage_block(diff_storage);
+ if (unlikely(!storage_block)) {
+ atomic_inc(&diff_storage->overflow_flag);
+ ret = -ENOSPC;
+ break;
+ }
+
+ available = storage_block->count - storage_block->used;
+ if (likely(available >= count)) {
+ diff_region->bdev = storage_block->bdev;
+ diff_region->sector =
+ storage_block->sector + storage_block->used;
+ diff_region->count = count;
+
+ storage_block->used += count;
+ diff_storage->filled += count;
+ break;
+ }
+
+ list_del(&storage_block->link);
+ list_add_tail(&storage_block->link,
+ &diff_storage->filled_blocks);
+ /*
+ * If there is still free space in the storage block, but
+ * it is not enough to store a piece, then such a block is
+ * considered used.
+ * We believe that the storage blocks are large enough
+ * to accommodate several pieces entirely.
+ */
+ diff_storage->filled += available;
+ } while (1);
+ sectors_left = diff_storage->requested - diff_storage->filled;
+ spin_unlock(&diff_storage->lock);
+
+ if (ret) {
+ pr_err("Cannot get empty storage block\n");
+ diff_storage_free_region(diff_region);
+ return ERR_PTR(ret);
+ }
+
+ if ((sectors_left <= diff_storage_minimum) &&
+ (atomic_inc_return(&diff_storage->low_space_flag) == 1))
+ diff_storage_event_low(diff_storage);
+
+ return diff_region;
+}
diff --git a/drivers/block/blksnap/diff_storage.h b/drivers/block/blksnap/diff_storage.h
new file mode 100644
index 000000000000..f4385e19b6c9
--- /dev/null
+++ b/drivers/block/blksnap/diff_storage.h
@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+#include "event_queue.h"
+#include "big_buffer.h"
+
+struct diff_region;
+
+/**
+ * struct diff_storage - Difference storage.
+ *
+ * @kref:
+ * The reference counter.
+ * @lock:
+ * Spinlock allows to guarantee the safety of linked lists.
+ * @storage_bdevs:
+ * List of opened block devices. Blocks for storing snapshot data can be
+ * located on different block devices. So, all opened block devices are
+ * located in this list. Blocks on opened block devices are allocated for
+ * storing the chunks data.
+ * @empty_blocks:
+ * List of empty blocks on storage. This list can be updated while
+ * holding a snapshot. This allows us to dynamically increase the
+ * storage size for these snapshots.
+ * @filled_blocks:
+ * List of filled blocks. When the blocks from the list of empty blocks are filled,
+ * we move them to the list of filled blocks.
+ * @capacity:
+ * Total amount of available storage space.
+ * @filled:
+ * The number of sectors already filled in.
+ * @requested:
+ * The number of sectors already requested from user space.
+ * @low_space_flag:
+ * The flag is set if the number of free regions available in the
+ * difference storage is less than the allowed minimum.
+ * @overflow_flag:
+ * The request for a free region failed due to the absence of free
+ * regions in the difference storage.
+ * @event_queue:
+ * A queue of events to pass events to user space. Diff storage and its
+ * owner can notify its snapshot about events like snapshot overflow,
+ * low free space and snapshot terminated.
+ *
+ * The difference storage manages the regions of block devices that are used
+ * to store the data of the original block devices in the snapshot.
+ * The difference storage is created one per snapshot and is used to store
+ * data from all the original snapshot block devices. At the same time, the
+ * difference storage itself can contain regions on various block devices.
+ */
+struct diff_storage {
+ struct kref kref;
+ spinlock_t lock;
+
+ struct list_head storage_bdevs;
+ struct list_head empty_blocks;
+ struct list_head filled_blocks;
+
+ sector_t capacity;
+ sector_t filled;
+ sector_t requested;
+
+ atomic_t low_space_flag;
+ atomic_t overflow_flag;
+
+ struct event_queue event_queue;
+};
+
+struct diff_storage *diff_storage_new(void);
+void diff_storage_free(struct kref *kref);
+
+static inline void diff_storage_get(struct diff_storage *diff_storage)
+{
+ kref_get(&diff_storage->kref);
+};
+static inline void diff_storage_put(struct diff_storage *diff_storage)
+{
+ if (likely(diff_storage))
+ kref_put(&diff_storage->kref, diff_storage_free);
+};
+
+int diff_storage_append_block(struct diff_storage *diff_storage, dev_t dev_id,
+ struct big_buffer *ranges,
+ unsigned int range_count);
+struct diff_region *diff_storage_new_region(struct diff_storage *diff_storage,
+ sector_t count);
+
+static inline void diff_storage_free_region(struct diff_region *region)
+{
+ kfree(region);
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+ if (region)
+ memory_object_dec(memory_object_diff_region);
+#endif
+}
--
2.20.1