[PATCH 11/20] block, blksnap: functions and structures for performing block I/O operations

Sergei Shtepa
2022-06-13T18:56:39Z

Provides synchronous and asynchronous block I/O operations for the
buffer of the minimum data storage block (struct diff_buffer).

Signed-off-by: Sergei Shtepa <sergei.shtepa@veeam.com>
---
drivers/block/blksnap/diff_io.c | 204 ++++++++++++++++++++++++++++++++
drivers/block/blksnap/diff_io.h | 122 +++++++++++++++++++
2 files changed, 326 insertions(+)
create mode 100644 drivers/block/blksnap/diff_io.c
create mode 100644 drivers/block/blksnap/diff_io.h

diff --git a/drivers/block/blksnap/diff_io.c b/drivers/block/blksnap/diff_io.c
new file mode 100644
index 000000000000..0be179c461d9
--- /dev/null
+++ b/drivers/block/blksnap/diff_io.c
@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0
+#define pr_fmt(fmt) KBUILD_MODNAME "-diff-io: " fmt
+#include <linux/blkdev.h>
+#include <linux/slab.h>
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+#include "memory_checker.h"
+#endif
+#include "diff_io.h"
+#include "diff_buffer.h"
+
+#define SECTORS_IN_PAGE (PAGE_SIZE / SECTOR_SIZE)
+
+struct bio_set diff_io_bioset = { 0 };
+
+int diff_io_init(void)
+{
+ return bioset_init(&diff_io_bioset, 64, 0,
+ BIOSET_NEED_BVECS | BIOSET_NEED_RESCUER);
+}
+
+void diff_io_done(void)
+{
+ bioset_exit(&diff_io_bioset);
+}
+
+static void diff_io_notify_cb(struct work_struct *work)
+{
+ struct diff_io_async *async =
+ container_of(work, struct diff_io_async, work);
+
+ might_sleep();
+ async->notify_cb(async->ctx);
+}
+
+static void diff_io_endio(struct bio *bio)
+{
+ struct diff_io *diff_io = bio->bi_private;
+
+ if (bio->bi_status != BLK_STS_OK)
+ diff_io->error = -EIO;
+
+ if (atomic_dec_and_test(&diff_io->bio_count)) {
+ if (diff_io->is_sync_io)
+ complete(&diff_io->notify.sync.completion);
+ else
+ queue_work(system_wq, &diff_io->notify.async.work);
+ }
+
+ bio_put(bio);
+}
+
+static inline struct diff_io *diff_io_new(bool is_write, bool is_nowait)
+{
+ struct diff_io *diff_io;
+ gfp_t gfp_mask = is_nowait ? (GFP_NOIO | GFP_NOWAIT) : GFP_NOIO;
+
+ diff_io = kzalloc(sizeof(struct diff_io), gfp_mask);
+ if (unlikely(!diff_io))
+ return NULL;
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+ memory_object_inc(memory_object_diff_io);
+#endif
+ diff_io->error = 0;
+ diff_io->is_write = is_write;
+ atomic_set(&diff_io->bio_count, 0);
+
+ return diff_io;
+}
+
+struct diff_io *diff_io_new_sync(bool is_write)
+{
+ struct diff_io *diff_io;
+
+ diff_io = diff_io_new(is_write, false);
+ if (unlikely(!diff_io))
+ return NULL;
+
+ diff_io->is_sync_io = true;
+ init_completion(&diff_io->notify.sync.completion);
+ return diff_io;
+}
+
+struct diff_io *diff_io_new_async(bool is_write, bool is_nowait,
+ void (*notify_cb)(void *ctx), void *ctx)
+{
+ struct diff_io *diff_io;
+
+ diff_io = diff_io_new(is_write, is_nowait);
+ if (unlikely(!diff_io))
+ return NULL;
+
+ diff_io->is_sync_io = false;
+ INIT_WORK(&diff_io->notify.async.work, diff_io_notify_cb);
+ diff_io->notify.async.ctx = ctx;
+ diff_io->notify.async.notify_cb = notify_cb;
+ return diff_io;
+}
+
+static inline bool check_page_aligned(sector_t sector)
+{
+ return !(sector & ((1ULL << (PAGE_SHIFT - SECTOR_SHIFT)) - 1));
+}
+
+static inline unsigned short calc_page_count(sector_t sectors)
+{
+ return round_up(sectors, SECTOR_IN_PAGE) / SECTOR_IN_PAGE;
+}
+
+int diff_io_do(struct diff_io *diff_io, struct diff_region *diff_region,
+ struct diff_buffer *diff_buffer, const bool is_nowait)
+{
+ int ret = 0;
+ struct bio *bio = NULL;
+ struct bio *flush_bio = NULL;
+ struct page **current_page_ptr;
+ unsigned int opf;
+ gfp_t gfp;
+ unsigned short nr_iovecs;
+ sector_t processed = 0;
+
+ if (unlikely(!check_page_aligned(diff_region->sector))) {
+ pr_err("Difference storage block should be aligned to PAGE_SIZE\n");
+ ret = -EINVAL;
+ goto fail;
+ }
+
+ nr_iovecs = calc_page_count(diff_region->count);
+ if (unlikely(nr_iovecs > diff_buffer->page_count)) {
+ pr_err("The difference storage block is larger than the buffer size\n");
+ ret = -EINVAL;
+ goto fail;
+ }
+
+ // Allocate both bios
+ opf = diff_io->is_write ? REQ_OP_WRITE : REQ_OP_READ;
+ gfp = GFP_NOIO | (is_nowait ? GFP_NOWAIT : 0);
+
+ bio = bio_alloc_bioset(diff_region->bdev, nr_iovecs,
+ opf | REQ_SYNC | REQ_IDLE | REQ_FUA,
+ gfp, &diff_io_bioset);
+ if (unlikely(!bio)) {
+ if (is_nowait)
+ ret = -EAGAIN;
+ else
+ ret = -ENOMEM;
+ goto fail;
+ }
+
+ flush_bio = bio_alloc_bioset(diff_region->bdev, 0,
+ opf | REQ_SYNC | REQ_PREFLUSH,
+ gfp, &diff_io_bioset);
+ if (unlikely(!flush_bio)) {
+ if (is_nowait)
+ ret = -EAGAIN;
+ else
+ ret = -ENOMEM;
+ goto fail;
+ }
+
+ atomic_set(&diff_io->bio_count, 2);
+
+ // Submit bio with datas
+ bio_set_flag(bio, BIO_FILTERED);
+ bio->bi_end_io = diff_io_endio;
+ bio->bi_private = diff_io;
+ bio->bi_iter.bi_sector = diff_region->sector;
+
+ current_page_ptr = diff_buffer->pages;
+ while (processed < diff_region->count) {
+ sector_t bvec_len_sect;
+ unsigned int bvec_len;
+
+ bvec_len_sect = min_t(sector_t, SECTORS_IN_PAGE,
+ diff_region->count - processed);
+ bvec_len = (unsigned int)(bvec_len_sect << SECTOR_SHIFT);
+
+ if (bio_add_page(bio, *current_page_ptr, bvec_len, 0) == 0) {
+ bio_put(bio);
+ return -EFAULT;
+ }
+
+ current_page_ptr++;
+ processed += bvec_len_sect;
+ }
+ submit_bio_noacct(bio);
+
+ // Submit flush bio
+ bio_set_flag(flush_bio, BIO_FILTERED);
+ flush_bio->bi_end_io = diff_io_endio;
+ flush_bio->bi_private = diff_io;
+ flush_bio->bi_iter.bi_sector = 0;
+ submit_bio_noacct(flush_bio);
+
+ if (diff_io->is_sync_io)
+ wait_for_completion_io(&diff_io->notify.sync.completion);
+
+ return 0;
+fail:
+ if (bio)
+ bio_put(bio);
+ if (flush_bio)
+ bio_put(flush_bio);
+ return ret;
+}
diff --git a/drivers/block/blksnap/diff_io.h b/drivers/block/blksnap/diff_io.h
new file mode 100644
index 000000000000..40cd3d88c838
--- /dev/null
+++ b/drivers/block/blksnap/diff_io.h
@@ -0,0 +1,122 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+#include <linux/workqueue.h>
+#include <linux/completion.h>
+
+struct diff_buffer;
+
+/**
+ * struct diff_region - Describes the location of the chunks data on
+ * difference storage.
+ * @bdev:
+ * The target block device.
+ * @sector:
+ * The sector offset of the region's first sector.
+ * @count:
+ * The count of sectors in the region.
+ */
+struct diff_region {
+ struct block_device *bdev;
+ sector_t sector;
+ sector_t count;
+};
+
+/**
+ * struct diff_io_sync - Structure for notification about completion of
+ * synchronous I/O.
+ * @completion:
+ * Indicates that the request has been processed.
+ *
+ * Allows to wait for completion of the I/O operation in the
+ * current thread.
+ */
+struct diff_io_sync {
+ struct completion completion;
+};
+
+/**
+ * struct diff_io_async - Structure for notification about completion of
+ * asynchronous I/O.
+ * @work:
+ * The &struct work_struct allows to schedule execution of an I/O operation
+ * in a separate process.
+ * @notify_cb:
+ * A pointer to the callback function that will be executed when
+ * the I/O execution is completed.
+ * @ctx:
+ * The context for the callback function &notify_cb.
+ *
+ * Allows to schedule execution of an I/O operation.
+ */
+struct diff_io_async {
+ struct work_struct work;
+ void (*notify_cb)(void *ctx);
+ void *ctx;
+};
+
+/**
+ * struct diff_io - Structure for I/O maintenance.
+ * @error:
+ * Zero if the I/O operation is successful, or an error code if it fails.
+ * @bio_count:
+ * The count of bio in the I/O request.
+ * @is_write:
+ * Indicates that a write operation is being performed.
+ * @is_sync_io:
+ * Indicates that the operation is being performed synchronously.
+ * @notify:
+ * This union may contain the diff_io_sync or diff_io_async structure
+ * for synchronous or asynchronous request.
+ *
+ * The request to perform an I/O operation is executed for a region of sectors.
+ * Such a region may contain several bios. It is necessary to notify about the
+ * completion of processing of all bios. The diff_io structure allows to do it.
+ */
+struct diff_io {
+ int error;
+ atomic_t bio_count;
+ bool is_write;
+ bool is_sync_io;
+ union {
+ struct diff_io_sync sync;
+ struct diff_io_async async;
+ } notify;
+};
+
+int diff_io_init(void);
+void diff_io_done(void);
+
+static inline void diff_io_free(struct diff_io *diff_io)
+{
+ kfree(diff_io);
+#ifdef CONFIG_BLK_SNAP_DEBUG_MEMORY_LEAK
+ if (diff_io)
+ memory_object_dec(memory_object_diff_io);
+#endif
+}
+
+struct diff_io *diff_io_new_sync(bool is_write);
+static inline struct diff_io *diff_io_new_sync_read(void)
+{
+ return diff_io_new_sync(false);
+};
+static inline struct diff_io *diff_io_new_sync_write(void)
+{
+ return diff_io_new_sync(true);
+};
+
+struct diff_io *diff_io_new_async(bool is_write, bool is_nowait,
+ void (*notify_cb)(void *ctx), void *ctx);
+static inline struct diff_io *
+diff_io_new_async_read(void (*notify_cb)(void *ctx), void *ctx, bool is_nowait)
+{
+ return diff_io_new_async(false, is_nowait, notify_cb, ctx);
+};
+static inline struct diff_io *
+diff_io_new_async_write(void (*notify_cb)(void *ctx), void *ctx, bool is_nowait)
+{
+ return diff_io_new_async(true, is_nowait, notify_cb, ctx);
+};
+
+int diff_io_do(struct diff_io *diff_io, struct diff_region *diff_region,
+ struct diff_buffer *diff_buffer, const bool is_nowait);
--
2.20.1