lvm-snap.c

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		/* don't go beyond the end */
		if (idx + 1 >= lv_snap->lv_remap_end) goto good_out;

		memset(lv_COW_table, 0, blksize_snap);

		if (end_of_table)
		{
			idx++;
			snap_phys_dev = lv_snap->lv_block_exception[idx].rdev_new;
			snap_pe_start = lv_snap->lv_block_exception[idx - (idx % COW_entries_per_pe)].rsector_new - lv_snap->lv_chunk_size;
			blksize_snap = lvm_get_blksize(snap_phys_dev);
			blocks[0] = snap_pe_start >> (blksize_snap >> 10);
		} else blocks[0]++;

		if (brw_kiovec(WRITE, 1, &iobuf, snap_phys_dev,
			       blocks, blksize_snap) != blksize_snap)
			goto fail_raw_write;
	}


 good_out:
	iobuf->length = length_tmp;
        iobuf->maplist[0] = page_tmp;
	iobuf->nr_pages = nr_pages_tmp;
	return 0;

	/* slow path */
 out:
	lvm_drop_snapshot(lv_snap, reason);
	return 1;

 fail_raw_write:
	reason = "write error";
	goto out;
}

/*
 * copy on write handler for one snapshot logical volume
 *
 * read the original blocks and store it/them on the new one(s).
 * if there is no exception storage space free any longer --> release snapshot.
 *
 * this routine gets called for each _first_ write to a physical chunk.
 */
int lvm_snapshot_COW(kdev_t org_phys_dev,
		     unsigned long org_phys_sector,
		     unsigned long org_pe_start,
		     unsigned long org_virt_sector,
		     lv_t * lv_snap)
{
	const char * reason;
	unsigned long org_start, snap_start, snap_phys_dev, virt_start, pe_off;
	int idx = lv_snap->lv_remap_ptr, chunk_size = lv_snap->lv_chunk_size;
	struct kiobuf * iobuf;
	unsigned long blocks[KIO_MAX_SECTORS];
	int blksize_snap, blksize_org, min_blksize, max_blksize;
	int max_sectors, nr_sectors;

	/* check if we are out of snapshot space */
	if (idx >= lv_snap->lv_remap_end)
		goto fail_out_of_space;

	/* calculate physical boundaries of source chunk */
	pe_off = org_pe_start % chunk_size;
	org_start = org_phys_sector - ((org_phys_sector-pe_off) % chunk_size);
	virt_start = org_virt_sector - (org_phys_sector - org_start);

	/* calculate physical boundaries of destination chunk */
	snap_phys_dev = lv_snap->lv_block_exception[idx].rdev_new;
	snap_start = lv_snap->lv_block_exception[idx].rsector_new;

#ifdef DEBUG_SNAPSHOT
	printk(KERN_INFO
	       "%s -- COW: "
	       "org %02d:%02d faulting %lu start %lu, "
	       "snap %02d:%02d start %lu, "
	       "size %d, pe_start %lu pe_off %lu, virt_sec %lu\n",
	       lvm_name,
	       MAJOR(org_phys_dev), MINOR(org_phys_dev), org_phys_sector,
	       org_start,
	       MAJOR(snap_phys_dev), MINOR(snap_phys_dev), snap_start,
	       chunk_size,
	       org_pe_start, pe_off,
	       org_virt_sector);
#endif

	iobuf = lv_snap->lv_iobuf;

	blksize_org = lvm_get_blksize(org_phys_dev);
	blksize_snap = lvm_get_blksize(snap_phys_dev);
	max_blksize = max(blksize_org, blksize_snap);
	min_blksize = min(blksize_org, blksize_snap);
	max_sectors = KIO_MAX_SECTORS * (min_blksize>>9);

	if (chunk_size % (max_blksize>>9))
		goto fail_blksize;

	while (chunk_size)
	{
		nr_sectors = min(chunk_size, max_sectors);
		chunk_size -= nr_sectors;

		iobuf->length = nr_sectors << 9;

		lvm_snapshot_prepare_blocks(blocks, org_start,
					    nr_sectors, blksize_org);
		if (brw_kiovec(READ, 1, &iobuf, org_phys_dev,
			       blocks, blksize_org) != (nr_sectors<<9))
			goto fail_raw_read;

		lvm_snapshot_prepare_blocks(blocks, snap_start,
					    nr_sectors, blksize_snap);
		if (brw_kiovec(WRITE, 1, &iobuf, snap_phys_dev,
			       blocks, blksize_snap) != (nr_sectors<<9))
			goto fail_raw_write;
	}

#ifdef DEBUG_SNAPSHOT
	/* invalidate the logical snapshot buffer cache */
	invalidate_snap_cache(virt_start, lv_snap->lv_chunk_size,
			      lv_snap->lv_dev);
#endif

	/* the original chunk is now stored on the snapshot volume
	   so update the execption table */
	lv_snap->lv_block_exception[idx].rdev_org = org_phys_dev;
	lv_snap->lv_block_exception[idx].rsector_org = org_start;

	lvm_hash_link(lv_snap->lv_block_exception + idx,
		      org_phys_dev, org_start, lv_snap);
	lv_snap->lv_remap_ptr = idx + 1;
	if (lv_snap->lv_snapshot_use_rate > 0) {
		if (lv_snap->lv_remap_ptr * 100 / lv_snap->lv_remap_end >= lv_snap->lv_snapshot_use_rate)
			wake_up_interruptible(&lv_snap->lv_snapshot_wait);
	}
	return 0;

	/* slow path */
 out:
	lvm_drop_snapshot(lv_snap, reason);
	return 1;

 fail_out_of_space:
	reason = "out of space";
	goto out;
 fail_raw_read:
	reason = "read error";
	goto out;
 fail_raw_write:
	reason = "write error";
	goto out;
 fail_blksize:
	reason = "blocksize error";
	goto out;
}

int lvm_snapshot_alloc_iobuf_pages(struct kiobuf * iobuf, int sectors)
{
	int bytes, nr_pages, err, i;

	bytes = sectors << 9;
	nr_pages = (bytes + ~PAGE_MASK) >> PAGE_SHIFT;
	err = expand_kiobuf(iobuf, nr_pages);
	if (err)
		goto out;

	err = -ENOMEM;
	iobuf->locked = 0;
	iobuf->nr_pages = 0;
	for (i = 0; i < nr_pages; i++)
	{
		struct page * page;

		page = alloc_page(GFP_KERNEL);
		if (!page)
			goto out;

		iobuf->maplist[i] = page;
		iobuf->nr_pages++;
	}
	iobuf->offset = 0;

	err = 0;
 out:
	return err;
}

static int calc_max_buckets(void)
{
	unsigned long mem;

	mem = num_physpages << PAGE_SHIFT;
	mem /= 100;
	mem *= 2;
	mem /= sizeof(struct list_head);

	return mem;
}

int lvm_snapshot_alloc_hash_table(lv_t * lv)
{
	int err;
	unsigned long buckets, max_buckets, size;
	struct list_head * hash;

	buckets = lv->lv_remap_end;
	max_buckets = calc_max_buckets();
	buckets = min(buckets, max_buckets);
	while (buckets & (buckets-1))
		buckets &= (buckets-1);

	size = buckets * sizeof(struct list_head);

	err = -ENOMEM;
	hash = vmalloc(size);
	lv->lv_snapshot_hash_table = hash;

	if (!hash)
		goto out;
	lv->lv_snapshot_hash_table_size = size;

	lv->lv_snapshot_hash_mask = buckets-1;
	while (buckets--)
		INIT_LIST_HEAD(hash+buckets);
	err = 0;
 out:
	return err;
}

int lvm_snapshot_alloc(lv_t * lv_snap)
{
	int err, blocksize, max_sectors;

	err = alloc_kiovec(1, &lv_snap->lv_iobuf);
	if (err)
		goto out;

	blocksize = lvm_blocksizes[MINOR(lv_snap->lv_dev)];
	max_sectors = KIO_MAX_SECTORS << (PAGE_SHIFT-9);

	err = lvm_snapshot_alloc_iobuf_pages(lv_snap->lv_iobuf, max_sectors);
	if (err)
		goto out_free_kiovec;

	err = lvm_snapshot_alloc_hash_table(lv_snap);
	if (err)
		goto out_free_kiovec;


		lv_snap->lv_COW_table_page = alloc_page(GFP_KERNEL);
		if (!lv_snap->lv_COW_table_page)
			goto out_free_kiovec;

 out:
	return err;

 out_free_kiovec:
	unmap_kiobuf(lv_snap->lv_iobuf);
	free_kiovec(1, &lv_snap->lv_iobuf);
	vfree(lv_snap->lv_snapshot_hash_table);
	lv_snap->lv_snapshot_hash_table = NULL;
	goto out;
}

void lvm_snapshot_release(lv_t * lv)
{
	if (lv->lv_block_exception)
	{
		vfree(lv->lv_block_exception);
		lv->lv_block_exception = NULL;
	}
	if (lv->lv_snapshot_hash_table)
	{
		vfree(lv->lv_snapshot_hash_table);
		lv->lv_snapshot_hash_table = NULL;
		lv->lv_snapshot_hash_table_size = 0;
	}
	if (lv->lv_iobuf)
	{
		unmap_kiobuf(lv->lv_iobuf);
		free_kiovec(1, &lv->lv_iobuf);
		lv->lv_iobuf = NULL;
	}
	if (lv->lv_COW_table_page)
	{
		free_page((ulong)lv->lv_COW_table_page);
		lv->lv_COW_table_page = NULL;
	}
}