// SPDX-License-Identifier: GPL-2.0-only
/*
* Partial Parity Log for closing the RAID5 write hole
* Copyright (c) 2017, Intel Corporation.
*/
#include <linux/kernel.h>
#include <linux/blkdev.h>
#include <linux/slab.h>
#include <linux/crc32c.h>
#include <linux/async_tx.h>
#include <linux/raid/md_p.h>
#include "md.h"
#include "raid5.h"
#include "raid5-log.h"
/*
* PPL consists of a 4KB header (struct ppl_header) and at least 128KB for
* partial parity data. The header contains an array of entries
* (struct ppl_header_entry) which describe the logged write requests.
* Partial parity for the entries comes after the header, written in the same
* sequence as the entries:
*
* Header
* entry0
* ...
* entryN
* PP data
* PP for entry0
* ...
* PP for entryN
*
* An entry describes one or more consecutive stripe_heads, up to a full
* stripe. The modifed raid data chunks form an m-by-n matrix, where m is the
* number of stripe_heads in the entry and n is the number of modified data
* disks. Every stripe_head in the entry must write to the same data disks.
* An example of a valid case described by a single entry (writes to the first
* stripe of a 4 disk array, 16k chunk size):
*
* sh->sector dd0 dd1 dd2 ppl
* +-----+-----+-----+
* 0 | --- | --- | --- | +----+
* 8 | -W- | -W- | --- | | pp | data_sector = 8
* 16 | -W- | -W- | --- | | pp | data_size = 3 * 2 * 4k
* 24 | -W- | -W- | --- | | pp | pp_size = 3 * 4k
* +-----+-----+-----+ +----+
*
* data_sector is the first raid sector of the modified data, data_size is the
* total size of modified data and pp_size is the size of partial parity for
* this entr
