dm-dedup: implementation of the read-on-write procedure

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+/*
+ * Copyright (C) 2012-2014 Vasily Tarasov
+ * Copyright (C) 2012-2014 Geoff Kuenning
+ * Copyright (C) 2012-2014 Sonam Mandal
+ * Copyright (C) 2012-2014 Karthikeyani Palanisami
+ * Copyright (C) 2012-2014 Philip Shilane
+ * Copyright (C) 2012-2014 Sagar Trehan
+ * Copyright (C) 2012-2014 Erez Zadok
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-dedup-target.h"
+#include "dm-dedup-rw.h"
+#include "dm-dedup-kvstore.h"
+
+#define DMD_IO_SIZE	4096
+
+static uint64_t compute_sector(struct bio *bio,
+			       struct dedup_config *dc)
+{
+	uint64_t to_be_lbn;
+
+	to_be_lbn = bio->bi_iter.bi_sector;
+	to_be_lbn /= dc->sectors_per_block;
+	to_be_lbn *= dc->sectors_per_block;
+
+	return to_be_lbn;
+}
+
+static int fetch_whole_block(struct dedup_config *dc,
+			uint64_t pbn, struct page_list *pl)
+{
+	struct dm_io_request iorq;
+	struct dm_io_region where;
+	unsigned long error_bits;
+
+	where.bdev = dc->data_dev->bdev;
+	where.sector = pbn;
+	where.count = dc->sectors_per_block;
+
+	iorq.bi_rw = READ;
+	iorq.mem.type = DM_IO_PAGE_LIST;
+	iorq.mem.ptr.pl = pl;
+	iorq.mem.offset = 0;
+	iorq.notify.fn = NULL;
+	iorq.client = dc->io_client;
+
+	return dm_io(&iorq, 1, &where, &error_bits);
+}
+
+static int merge_data(struct dedup_config *dc, struct page *page,
+				struct bio *bio)
+{
+	void *src_page_vaddr, *dest_page_vaddr;
+	int position, err = 0;
+
+	/* Relative offset in terms of sector size */
+	position = (bio->bi_iter.bi_sector % dc->sectors_per_block);
+
+	if (!page || !bio->bi_io_vec->bv_page) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	src_page_vaddr = page_address(bio->bi_io_vec->bv_page);
+	dest_page_vaddr = page_address(page);
+
+	src_page_vaddr = src_page_vaddr + bio->bi_io_vec->bv_offset;
+	/* Locating the right sector to merge */
+	dest_page_vaddr = dest_page_vaddr + (to_bytes(position));
+
+	/* Merging Data */
+	memmove(dest_page_vaddr, src_page_vaddr, bio->bi_io_vec->bv_len);
+out:
+	return err;
+}
+
+static void copy_pages(struct page *src, struct bio *clone)
+{
+	void *src_page_vaddr, *dest_page_vaddr;
+
+	src_page_vaddr = page_address(src);
+	dest_page_vaddr = page_address(clone->bi_io_vec->bv_page);
+
+	memmove(dest_page_vaddr, src_page_vaddr, DMD_IO_SIZE);
+}
+
+static void my_endio(struct bio *clone, int error)
+{
+	unsigned rw = bio_data_dir(clone);
+	struct bio *orig;
+	struct bio_vec bv;
+
+	if (!error && !bio_flagged(clone, BIO_UPTODATE))
+		error = -EIO;
+
+	/* free the processed pages */
+	if (rw == WRITE || rw == READ) {
+		bv = bio_iovec(clone);
+		if (bv.bv_page) {
+			free_pages((unsigned long)page_address(bv.bv_page), 0);
+			bv.bv_page = NULL;
+		}
+	}
+
+	orig = clone->bi_private;
+	bio_endio(orig, 0);
+
+	bio_put(clone);
+}
+
+/*
+ * XXX: there  is existing zero_fill_bio() in the kernel,
+ * should we use it?
+ */
+static void my_zero_fill_bio(struct bio *bio)
+{
+	void *data;
+	unsigned int length;
+
+	data = bio_data(bio);
+	length = bio_cur_bytes(bio);
+	memset(data, 0, length);
+}
+
+static struct bio *create_bio(struct dedup_config *dc,
+			      struct bio *bio)
+{
+	struct bio *clone;
+	struct page *page;
+
+	clone = bio_kmalloc(GFP_NOIO, 1);
+	if (!clone)
+		goto out;
+
+	clone->bi_bdev = bio->bi_bdev;
+	clone->bi_rw = bio->bi_rw;
+	clone->bi_iter.bi_sector = compute_sector(bio, dc);
+	clone->bi_private = bio;  /* for later completion */
+	clone->bi_end_io = my_endio;
+
+	page = alloc_pages(GFP_NOIO, 0);
+	if (!page)
+		goto bad_putbio;
+
+	if (!bio_add_page(clone, page, DMD_IO_SIZE, 0))
+		goto bad_freepage;
+
+	goto out;
+
+bad_freepage:
+	free_pages((unsigned long) page_address(page), 0);
+bad_putbio:
+	bio_put(clone);
+	clone = NULL;
+out:
+	return clone;
+}
+
+static struct bio *prepare_bio_with_pbn(struct dedup_config *dc,
+					struct bio *bio, uint64_t pbn)
+{
+	int r = 0;
+	struct page_list *pl;
+	struct bio *clone = NULL;
+
+	pl = kmalloc(sizeof(pl), GFP_NOIO);
+	if (!pl)
+		goto out;
+
+	/*
+	 * Since target I/O size is 4KB currently, we need only one page to
+	 * store the data. However, if the target I/O size increases, we need
+	 * to allocate more pages and set this linked list correctly.
+	 */
+	pl->page = alloc_pages(GFP_NOIO, 0);
+	if (!pl->page)
+		goto out_allocfail;
+
+	pl->next = NULL;
+
+	r = fetch_whole_block(dc, pbn, pl);
+	if (r < 0)
+		goto out_fail;
+
+	r = merge_data(dc, pl->page, bio);
+	if (r < 0)
+		goto out_fail;
+
+	clone = create_bio(dc, bio);
+	if (!clone)
+		goto out_fail;
+
+	copy_pages(pl->page, clone);
+
+out_fail:
+	free_pages((unsigned long) page_address(pl->page), 0);
+out_allocfail:
+	kfree(pl);
+out:
+	return clone;
+}
+
+static struct bio *prepare_bio_without_pbn(struct dedup_config *dc,
+					   struct bio *bio)
+{
+	int r = 0;
+	struct bio *clone = NULL;
+
+	clone = create_bio(dc, bio);
+	if (!clone)
+		goto out;
+
+	my_zero_fill_bio(clone);
+
+	r = merge_data(dc, clone->bi_io_vec->bv_page, bio);
+	if (r < 0)
+		BUG();
+out:
+	return clone;
+}
+
+struct bio *prepare_bio_on_write(struct dedup_config *dc, struct bio *bio)
+{
+	int r;
+	uint64_t lbn_sector;
+	uint64_t lbn;
+	uint32_t vsize;
+	struct lbn_pbn_value lbnpbn_value;
+	struct bio *clone;
+
+	lbn_sector = compute_sector(bio, dc);
+	lbn = lbn_sector / dc->sectors_per_block;
+
+	/* check for old or new lbn and fetch the appropriate pbn */
+	r = dc->kvs_lbn_pbn->kvs_lookup(dc->kvs_lbn_pbn, (void *)&lbn,
+			sizeof(lbn), (void *)&lbnpbn_value, &vsize);
+	if (r == 0)
+		clone = prepare_bio_without_pbn(dc, bio);
+	else if (r == 1)
+		clone = prepare_bio_with_pbn(dc, bio, lbnpbn_value.pbn
+						* dc->sectors_per_block);
+	else
+		BUG();
+
+	return clone;
+}

new file mode 100644
index 0000000..ad12a27
@@ -0,0 +1,19 @@
+/*
+ * Copyright (C) 2012-2014 Vasily Tarasov
+ * Copyright (C) 2012-2014 Geoff Kuenning
+ * Copyright (C) 2012-2014 Sonam Mandal
+ * Copyright (C) 2012-2014 Karthikeyani Palanisami
+ * Copyright (C) 2012-2014 Philip Shilane
+ * Copyright (C) 2012-2014 Sagar Trehan
+ * Copyright (C) 2012-2014 Erez Zadok
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_DEDUP_RW_H
+#define DM_DEDUP_RW_H
+
+extern struct bio *prepare_bio_on_write(struct dedup_config *dc,
+							struct bio *bio);
+
+#endif /* DM_DEDUP_RW_H */