/*
 * Partial Parity Log for closing the RAID5 write hole
 * Copyright (c) 2017, Intel Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 */

#include <linux/kernel.h>
#include <linux/blkdev.h>
#include <linux/slab.h>
#include <linux/crc32c.h>
#include <linux/flex_array.h>
#include <linux/async_tx.h>
#include <linux/raid/md_p.h>
#include "md.h"
#include "raid5.h"

#define STRIPE_SIZE             PAGE_SIZE
#define STRIPE_SECTORS          (STRIPE_SIZE>>9)

/*
 * 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 entry. Entries for full stripe writes contain no partial parity
 * (pp_size = 0), they only mark the stripes for which parity should be
 * recalculated after an unclean shutdown. Every entry holds a checksum of its
 * partial parity, the header also has a checksum of the header itself.
 *
 * A write request is always logged to the PPL instance stored on the parity
 * disk of the corresponding stripe. For each member disk there is one ppl_log
 * used to handle logging for this disk, independently from others. They are
 * grouped in child_logs array in struct ppl_conf, which is assigned to
 * r5conf->log_private.
 *
 * ppl_io_unit represents a full PPL write, header_page contains the ppl_header.
 * PPL entries for logged stripes are added in ppl_log_stripe(). A stripe_head
 * can be appended to the last entry if it meets the conditions for a valid
 * entry described above, otherwise a new entry is added. Checksums of entries
 * are calculated incrementally as stripes containing partial parity are being
 * added. ppl_submit_iounit() calculates the checksum of the header and submits
 * a bio containing the header page and partial parity pages (sh->ppl_page) for
 * all stripes of the io_unit. When the PPL write completes, the stripes
 * associated with the io_unit are released and raid5d starts writing their data
 * and parity. When all stripes are written, the io_unit is freed and the next
 * can be submitted.
 *
 * An io_unit is used to gather stripes until it is submitted or becomes full
 * (if the maximum number of entries or size of PPL is reached). Another io_unit
 * can't be submitted until the previous has completed (PPL and stripe
 * data+parity is written). The log->io_list tracks all io_units of a log
 * (for a single member disk). New io_units are added to the end of the list
 * and the first io_unit is submitted, if it is not submitted already.
 * The current io_unit accepting new stripes is always at the end of the list.
 */

#define PPL_SPACE_SIZE (128 * 1024)

struct ppl_conf {
        struct mddev *mddev;

        /* array of child logs, one for each raid disk */
        struct ppl_log *child_logs;
        int count;

        int block_size;         /* the logical block size used for data_sector
                                 * in ppl_header_entry */
        u32 signature;          /* raid array identifier */
        atomic64_t seq;         /* current log write sequence number */

        struct kmem_cache *io_kc;
        mempool_t *io_pool;
        struct bio_set *bs;

        /* used only for recovery */
        int recovered_entries;
        int mismatch_count;

        /* stripes to retry if failed to allocate io_unit */
        struct list_head no_mem_stripes;
        spinlock_t no_mem_stripes_lock;
};

struct ppl_log {
        struct ppl_conf *ppl_conf;      /* shared between all log instances */

        struct md_rdev *rdev;           /* array member disk associated with
                                         * this log instance */
        struct mutex io_mutex;
        struct ppl_io_unit *current_io; /* current io_unit accepting new data
                                         * always at the end of io_list */
        spinlock_t io_list_lock;
        struct list_head io_list;       /* all io_units of this log */

        sector_t next_io_sector;
        unsigned int entry_space;
        bool use_multippl;
};

#define PPL_IO_INLINE_BVECS 32

struct ppl_io_unit {
        struct ppl_log *log;

        struct page *header_page;       /* for ppl_header */

        unsigned int entries_count;     /* number of entries in ppl_header */
        unsigned int pp_size;           /* total size current of partial parity */

        u64 seq;                        /* sequence number of this log write */
        struct list_head log_sibling;   /* log->io_list */

        struct list_head stripe_list;   /* stripes added to the io_unit */
        atomic_t pending_stripes;       /* how many stripes not written to raid */

        bool submitted;                 /* true if write to log started */

        /* inline bio and its biovec for submitting the iounit */
        struct bio bio;
        struct bio_aux bio_aux;
        struct bio_vec biovec[PPL_IO_INLINE_BVECS];
};

struct dma_async_tx_descriptor *
ops_run_partial_parity(struct stripe_head *sh, struct raid5_percpu *percpu,
                       struct dma_async_tx_descriptor *tx)
{
        int disks = sh->disks;
        struct page **srcs = flex_array_get(percpu->scribble, 0);
        int count = 0, pd_idx = sh->pd_idx, i;
        struct async_submit_ctl submit;

        pr_debug("%s: stripe %llu\n", __func__, (unsigned long long)sh->sector);

        /*
         * Partial parity is the XOR of stripe data chunks that are not changed
         * during the write request. Depending on available data
         * (read-modify-write vs. reconstruct-write case) we calculate it
         * differently.
         */
        if (sh->reconstruct_state == reconstruct_state_prexor_drain_run) {
                /*
                 * rmw: xor old data and parity from updated disks
                 * This is calculated earlier by ops_run_prexor5() so just copy
                 * the parity dev page.
                 */
                srcs[count++] = sh->dev[pd_idx].page;
        } else if (sh->reconstruct_state == reconstruct_state_drain_run) {
                /* rcw: xor data from all not updated disks */
                for (i = disks; i--;) {
                        struct r5dev *dev = &sh->dev[i];
                        if (test_bit(R5_UPTODATE, &dev->flags))
                                srcs[count++] = dev->page;
                }
        } else {
                return tx;
        }

        init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST, tx,
                          NULL, sh, flex_array_get(percpu->scribble, 0)
                          + sizeof(struct page *) * (sh->disks + 2));

        if (count == 1)
                tx = async_memcpy(sh->ppl_page, srcs[0], 0, 0, PAGE_SIZE,
                                  &submit);
        else
                tx = async_xor(sh->ppl_page, srcs, 0, count, PAGE_SIZE,
                               &submit);

        return tx;
}

static void *ppl_io_pool_alloc(gfp_t gfp_mask, void *pool_data)
{
        struct kmem_cache *kc = pool_data;
        struct ppl_io_unit *io;

        io = kmem_cache_alloc(kc, gfp_mask);
        if (!io)
                return NULL;

        io->header_page = alloc_page(gfp_mask);
        if (!io->header_page) {
                kmem_cache_free(kc, io);
                return NULL;
        }

        return io;
}

static void ppl_io_pool_free(void *element, void *pool_data)
{
        struct kmem_cache *kc = pool_data;
        struct ppl_io_unit *io = element;

        __free_page(io->header_page);
        kmem_cache_free(kc, io);
}

static struct ppl_io_unit *ppl_new_iounit(struct ppl_log *log,
                                          struct stripe_head *sh)
{
        struct ppl_conf *ppl_conf = log->ppl_conf;
        struct ppl_io_unit *io;
        struct ppl_header *pplhdr;
        struct page *header_page;

        io = mempool_alloc(ppl_conf->io_pool, GFP_NOWAIT);
        if (!io)
                return NULL;

        header_page = io->header_page;
        memset(io, 0, sizeof(*io));
        io->header_page = header_page;

        io->log = log;
        INIT_LIST_HEAD(&io->log_sibling);
        INIT_LIST_HEAD(&io->stripe_list);
        atomic_set(&io->pending_stripes, 0);
        bio_init(&io->bio);
        io->bio.bio_aux = &io->bio_aux;
        atomic_set(&io->bio.bio_aux->__bi_remaining, 1);
        io->bio.bi_io_vec = io->biovec;
        io->bio.bi_max_vecs = PPL_IO_INLINE_BVECS;

        pplhdr = page_address(io->header_page);
        clear_page(pplhdr);
        memset(pplhdr->reserved, 0xff, PPL_HDR_RESERVED);
        pplhdr->signature = cpu_to_le32(ppl_conf->signature);

        io->seq = atomic64_add_return(1, &ppl_conf->seq);
        pplhdr->generation = cpu_to_le64(io->seq);

        return io;
}

static int ppl_log_stripe(struct ppl_log *log, struct stripe_head *sh)
{
        struct ppl_io_unit *io = log->current_io;
        struct ppl_header_entry *e = NULL;
        struct ppl_header *pplhdr;
        int i;
        sector_t data_sector = 0;
        int data_disks = 0;
        struct r5conf *conf = sh->raid_conf;

        pr_debug("%s: stripe: %llu\n", __func__, (unsigned long long)sh->sector);

        /* check if current io_unit is full */
        if (io && (io->pp_size == log->entry_space ||
                   io->entries_count == PPL_HDR_MAX_ENTRIES)) {
                pr_debug("%s: add io_unit blocked by seq: %llu\n",
                         __func__, io->seq);
                io = NULL;
        }

        /* add a new unit if there is none or the current is full */
        if (!io) {
                io = ppl_new_iounit(log, sh);
                if (!io)
                        return -ENOMEM;
                spin_lock_irq(&log->io_list_lock);
                list_add_tail(&io->log_sibling, &log->io_list);
                spin_unlock_irq(&log->io_list_lock);

                log->current_io = io;
        }

        for (i = 0; i < sh->disks; i++) {
                struct r5dev *dev = &sh->dev[i];

                if (i != sh->pd_idx && test_bit(R5_Wantwrite, &dev->flags)) {
                        if (!data_disks || dev->sector < data_sector)
                                data_sector = dev->sector;
                        data_disks++;
                }
        }
        BUG_ON(!data_disks);

        pr_debug("%s: seq: %llu data_sector: %llu data_disks: %d\n", __func__,
                 io->seq, (unsigned long long)data_sector, data_disks);

        pplhdr = page_address(io->header_page);

        if (io->entries_count > 0) {
                struct ppl_header_entry *last =
                                &pplhdr->entries[io->entries_count - 1];
                struct stripe_head *sh_last = list_last_entry(
                                &io->stripe_list, struct stripe_head, log_list);
                u64 data_sector_last = le64_to_cpu(last->data_sector);
                u32 data_size_last = le32_to_cpu(last->data_size);

                /*
                 * Check if we can append the stripe to the last entry. It must
                 * be just after the last logged stripe and write to the same
                 * disks. Use bit shift and logarithm to avoid 64-bit division.
                 */
                if ((sh->sector == sh_last->sector + STRIPE_SECTORS) &&
                    (data_sector >> ilog2(conf->chunk_sectors) ==
                     data_sector_last >> ilog2(conf->chunk_sectors)) &&
                    ((data_sector - data_sector_last) * data_disks ==
                     data_size_last >> 9))
                        e = last;
        }

        if (!e) {
                e = &pplhdr->entries[io->entries_count++];
                e->data_sector = cpu_to_le64(data_sector);
                e->parity_disk = cpu_to_le32(sh->pd_idx);
                e->checksum = cpu_to_le32(~0);
        }

        le32_add_cpu(&e->data_size, data_disks << PAGE_SHIFT);

        /* don't write any PP if full stripe write */
        if (!test_bit(STRIPE_FULL_WRITE, &sh->state)) {
                le32_add_cpu(&e->pp_size, PAGE_SIZE);
                io->pp_size += PAGE_SIZE;
                e->checksum = cpu_to_le32(crc32c_le(le32_to_cpu(e->checksum),
                                                    page_address(sh->ppl_page),
                                                    PAGE_SIZE));
        }

        list_add_tail(&sh->log_list, &io->stripe_list);
        atomic_inc(&io->pending_stripes);
        sh->ppl_io = io;

        return 0;
}

int ppl_write_stripe(struct r5conf *conf, struct stripe_head *sh)
{
        struct ppl_conf *ppl_conf = conf->log_private;
        struct ppl_io_unit *io = sh->ppl_io;
        struct ppl_log *log;

        if (io || test_bit(STRIPE_SYNCING, &sh->state) || !sh->ppl_page ||
            !test_bit(R5_Wantwrite, &sh->dev[sh->pd_idx].flags) ||
            !test_bit(R5_Insync, &sh->dev[sh->pd_idx].flags)) {
                clear_bit(STRIPE_LOG_TRAPPED, &sh->state);
                return -EAGAIN;
        }

        log = &ppl_conf->child_logs[sh->pd_idx];

        mutex_lock(&log->io_mutex);

        if (!log->rdev || test_bit(Faulty, &log->rdev->flags)) {
                mutex_unlock(&log->io_mutex);
                return -EAGAIN;
        }

        set_bit(STRIPE_LOG_TRAPPED, &sh->state);
        clear_bit(STRIPE_DELAYED, &sh->state);
        atomic_inc(&sh->count);

        if (ppl_log_stripe(log, sh)) {
                spin_lock_irq(&ppl_conf->no_mem_stripes_lock);
                list_add_tail(&sh->log_list, &ppl_conf->no_mem_stripes);
                spin_unlock_irq(&ppl_conf->no_mem_stripes_lock);
        }

        mutex_unlock(&log->io_mutex);

        return 0;
}

static void ppl_log_endio(struct bio *bio, int error)
{
        struct ppl_io_unit *io = bio->bi_private;
        struct ppl_log *log = io->log;
        struct ppl_conf *ppl_conf = log->ppl_conf;
        struct stripe_head *sh, *next;

        pr_debug("%s: seq: %llu\n", __func__, io->seq);

        if (error)
                md_error(ppl_conf->mddev, log->rdev);

        list_for_each_entry_safe(sh, next, &io->stripe_list, log_list) {
                list_del_init(&sh->log_list);

                set_bit(STRIPE_HANDLE, &sh->state);
                raid5_release_stripe(sh);
        }
}

static void ppl_submit_iounit_bio(struct ppl_io_unit *io, struct bio *bio)
{
        char b[BDEVNAME_SIZE];

        pr_debug("%s: seq: %llu size: %u sector: %llu dev: %s\n",
                 __func__, io->seq, bio->bi_size,
                 (unsigned long long)bio->bi_sector,
                 bdevname(bio->bi_bdev, b));

        submit_bio(bio->bi_rw, bio);
}

static void ppl_submit_iounit(struct ppl_io_unit *io)
{
        struct ppl_log *log = io->log;
        struct ppl_conf *ppl_conf = log->ppl_conf;
        struct ppl_header *pplhdr = page_address(io->header_page);
        struct bio *bio = &io->bio;
        struct stripe_head *sh;
        int i;

        bio->bi_private = io;

        if (!log->rdev || test_bit(Faulty, &log->rdev->flags)) {
                ppl_log_endio(bio,0);
                return;
        }

        for (i = 0; i < io->entries_count; i++) {
                struct ppl_header_entry *e = &pplhdr->entries[i];

                pr_debug("%s: seq: %llu entry: %d data_sector: %llu pp_size: %u data_size: %u\n",
                         __func__, io->seq, i, le64_to_cpu(e->data_sector),
                         le32_to_cpu(e->pp_size), le32_to_cpu(e->data_size));

                e->data_sector = cpu_to_le64(le64_to_cpu(e->data_sector) >>
                                             ilog2(ppl_conf->block_size >> 9));
                e->checksum = cpu_to_le32(~le32_to_cpu(e->checksum));
        }

        pplhdr->entries_count = cpu_to_le32(io->entries_count);
        pplhdr->checksum = cpu_to_le32(~crc32c_le(~0, pplhdr, PPL_HEADER_SIZE));

        /* Rewind the buffer if current PPL is larger then remaining space */
        if (log->use_multippl &&
            log->rdev->ppl.sector + log->rdev->ppl.size - log->next_io_sector <
            (PPL_HEADER_SIZE + io->pp_size) >> 9)
                log->next_io_sector = log->rdev->ppl.sector;


        bio->bi_end_io = ppl_log_endio;
        bio->bi_rw = WRITE_FUA;
        bio->bi_bdev = log->rdev->bdev;
        bio->bi_sector = log->next_io_sector;
        bio_add_page(bio, io->header_page, PAGE_SIZE, 0);

        pr_debug("%s: log->current_io_sector: %llu\n", __func__,
            (unsigned long long)log->next_io_sector);

        if (log->use_multippl)
                log->next_io_sector += (PPL_HEADER_SIZE + io->pp_size) >> 9;

        list_for_each_entry(sh, &io->stripe_list, log_list) {
                /* entries for full stripe writes have no partial parity */
                if (test_bit(STRIPE_FULL_WRITE, &sh->state))
                        continue;

                if (!bio_add_page(bio, sh->ppl_page, PAGE_SIZE, 0)) {
                        struct bio *prev = bio;

                        bio = bio_alloc_bioset(GFP_NOIO, BIO_MAX_PAGES,
                                               ppl_conf->bs);
                        bio->bi_rw = prev->bi_rw;
                        bio->bi_bdev = prev->bi_bdev;
                        bio->bi_sector = bio_end_sector(prev);
                        bio_add_page(bio, sh->ppl_page, PAGE_SIZE, 0);

                        bio_chain(bio, prev);
                        ppl_submit_iounit_bio(io, prev);
                }
        }

        ppl_submit_iounit_bio(io, bio);
}

static void ppl_submit_current_io(struct ppl_log *log)
{
        struct ppl_io_unit *io;

        spin_lock_irq(&log->io_list_lock);

        io = list_first_entry_or_null(&log->io_list, struct ppl_io_unit,
                                      log_sibling);
        if (io && io->submitted)
                io = NULL;

        spin_unlock_irq(&log->io_list_lock);

        if (io) {
                io->submitted = true;

                if (io == log->current_io)
                        log->current_io = NULL;

                ppl_submit_iounit(io);
        }
}

void ppl_write_stripe_run(struct r5conf *conf)
{
        struct ppl_conf *ppl_conf = conf->log_private;
        struct ppl_log *log;
        int i;

        for (i = 0; i < ppl_conf->count; i++) {
                log = &ppl_conf->child_logs[i];

                mutex_lock(&log->io_mutex);
                ppl_submit_current_io(log);
                mutex_unlock(&log->io_mutex);
        }
}

static void ppl_io_unit_finished(struct ppl_io_unit *io)
{
        struct ppl_log *log = io->log;
        struct ppl_conf *ppl_conf = log->ppl_conf;
        unsigned long flags;

        pr_debug("%s: seq: %llu\n", __func__, io->seq);

        local_irq_save(flags);

        spin_lock(&log->io_list_lock);
        list_del(&io->log_sibling);
        spin_unlock(&log->io_list_lock);

        mempool_free(io, ppl_conf->io_pool);

        spin_lock(&ppl_conf->no_mem_stripes_lock);
        if (!list_empty(&ppl_conf->no_mem_stripes)) {
                struct stripe_head *sh;

                sh = list_first_entry(&ppl_conf->no_mem_stripes,
                                      struct stripe_head, log_list);
                list_del_init(&sh->log_list);
                set_bit(STRIPE_HANDLE, &sh->state);
                raid5_release_stripe(sh);
        }
        spin_unlock(&ppl_conf->no_mem_stripes_lock);

        local_irq_restore(flags);
}

void ppl_stripe_write_finished(struct stripe_head *sh)
{
        struct ppl_io_unit *io;

        io = sh->ppl_io;
        sh->ppl_io = NULL;

        if (io && atomic_dec_and_test(&io->pending_stripes))
                ppl_io_unit_finished(io);
}

static void ppl_xor(int size, struct page *page1, struct page *page2)
{
        struct async_submit_ctl submit;
        struct dma_async_tx_descriptor *tx;
        struct page *xor_srcs[] = { page1, page2 };

        init_async_submit(&submit, ASYNC_TX_ACK|ASYNC_TX_XOR_DROP_DST,
                          NULL, NULL, NULL, NULL);
        tx = async_xor(page1, xor_srcs, 0, 2, size, &submit);

        async_tx_quiesce(&tx);
}

/*
 * PPL recovery strategy: xor partial parity and data from all modified data
 * disks within a stripe and write the result as the new stripe parity. If all
 * stripe data disks are modified (full stripe write), no partial parity is
 * available, so just xor the data disks.
 *
 * Recovery of a PPL entry shall occur only if all modified data disks are
 * available and read from all of them succeeds.
 *
 * A PPL entry applies to a stripe, partial parity size for an entry is at most
 * the size of the chunk. Examples of possible cases for a single entry:
 *
 * case 0: single data disk write:
 *   data0    data1    data2     ppl        parity
 * +--------+--------+--------+           +--------------------+
 * | ------ | ------ | ------ | +----+    | (no change)        |
 * | ------ | -data- | ------ | | pp | -> | data1 ^ pp         |
 * | ------ | -data- | ------ | | pp | -> | data1 ^ pp         |
 * | ------ | ------ | ------ | +----+    | (no change)        |
 * +--------+--------+--------+           +--------------------+
 * pp_size = data_size
 *
 * case 1: more than one data disk write:
 *   data0    data1    data2     ppl        parity
 * +--------+--------+--------+           +--------------------+
 * | ------ | ------ | ------ | +----+    | (no change)        |
 * | -data- | -data- | ------ | | pp | -> | data0 ^ data1 ^ pp |
 * | -data- | -data- | ------ | | pp | -> | data0 ^ data1 ^ pp |
 * | ------ | ------ | ------ | +----+    | (no change)        |
 * +--------+--------+--------+           +--------------------+
 * pp_size = data_size / modified_data_disks
 *
 * case 2: write to all data disks (also full stripe write):
 *   data0    data1    data2                parity
 * +--------+--------+--------+           +--------------------+
 * | ------ | ------ | ------ |           | (no change)        |
 * | -data- | -data- | -data- | --------> | xor all data       |
 * | ------ | ------ | ------ | --------> | (no change)        |
 * | ------ | ------ | ------ |           | (no change)        |
 * +--------+--------+--------+           +--------------------+
 * pp_size = 0
 *
 * The following cases are possible only in other implementations. The recovery
 * code can handle them, but they are not generated at runtime because they can
 * be reduced to cases 0, 1 and 2:
 *
 * case 3:
 *   data0    data1    data2     ppl        parity
 * +--------+--------+--------+ +----+    +--------------------+
 * | ------ | -data- | -data- | | pp |    | data1 ^ data2 ^ pp |
 * | ------ | -data- | -data- | | pp | -> | data1 ^ data2 ^ pp |
 * | -data- | -data- | -data- | | -- | -> | xor all data       |
 * | -data- | -data- | ------ | | pp |    | data0 ^ data1 ^ pp |
 * +--------+--------+--------+ +----+    +--------------------+
 * pp_size = chunk_size
 *
 * case 4:
 *   data0    data1    data2     ppl        parity
 * +--------+--------+--------+ +----+    +--------------------+
 * | ------ | -data- | ------ | | pp |    | data1 ^ pp         |
 * | ------ | ------ | ------ | | -- | -> | (no change)        |
 * | ------ | ------ | ------ | | -- | -> | (no change)        |
 * | -data- | ------ | ------ | | pp |    | data0 ^ pp         |
 * +--------+--------+--------+ +----+    +--------------------+
 * pp_size = chunk_size
 */
static int ppl_recover_entry(struct ppl_log *log, struct ppl_header_entry *e,
                             sector_t ppl_sector)
{
        struct ppl_conf *ppl_conf = log->ppl_conf;
        struct mddev *mddev = ppl_conf->mddev;
        struct r5conf *conf = mddev->private;
        int block_size = ppl_conf->block_size;
        struct page *page1;
        struct page *page2;
        sector_t r_sector_first;
        sector_t r_sector_last;
        int strip_sectors;
        int data_disks;
        int i;
        int ret = 0;
        char b[BDEVNAME_SIZE];
        unsigned int pp_size = le32_to_cpu(e->pp_size);
        unsigned int data_size = le32_to_cpu(e->data_size);

        page1 = alloc_page(GFP_KERNEL);
        page2 = alloc_page(GFP_KERNEL);

        if (!page1 || !page2) {
                ret = -ENOMEM;
                goto out;
        }

        r_sector_first = le64_to_cpu(e->data_sector) * (block_size >> 9);

        if ((pp_size >> 9) < conf->chunk_sectors) {
                if (pp_size > 0) {
                        data_disks = data_size / pp_size;
                        strip_sectors = pp_size >> 9;
                } else {
                        data_disks = conf->raid_disks - conf->max_degraded;
                        strip_sectors = (data_size >> 9) / data_disks;
                }
                r_sector_last = r_sector_first +
                                (data_disks - 1) * conf->chunk_sectors +
                                strip_sectors;
        } else {
                data_disks = conf->raid_disks - conf->max_degraded;
                strip_sectors = conf->chunk_sectors;
                r_sector_last = r_sector_first + (data_size >> 9);
        }

        pr_debug("%s: array sector first: %llu last: %llu\n", __func__,
                 (unsigned long long)r_sector_first,
                 (unsigned long long)r_sector_last);

        /* if start and end is 4k aligned, use a 4k block */
        if (block_size == 512 &&
            (r_sector_first & (STRIPE_SECTORS - 1)) == 0 &&
            (r_sector_last & (STRIPE_SECTORS - 1)) == 0)
                block_size = STRIPE_SIZE;

        /* iterate through blocks in strip */
        for (i = 0; i < strip_sectors; i += (block_size >> 9)) {
                bool update_parity = false;
                sector_t parity_sector;
                struct md_rdev *parity_rdev;
                struct stripe_head sh;
                int disk;
                int indent = 0;

                pr_debug("%s:%*s iter %d start\n", __func__, indent, "", i);
                indent += 2;

                memset(page_address(page1), 0, PAGE_SIZE);

                /* iterate through data member disks */
                for (disk = 0; disk < data_disks; disk++) {
                        int dd_idx;
                        struct md_rdev *rdev;
                        sector_t sector;
                        sector_t r_sector = r_sector_first + i +
                                            (disk * conf->chunk_sectors);

                        pr_debug("%s:%*s data member disk %d start\n",
                                 __func__, indent, "", disk);
                        indent += 2;

                        if (r_sector >= r_sector_last) {
                                pr_debug("%s:%*s array sector %llu doesn't need parity update\n",
                                         __func__, indent, "",
                                         (unsigned long long)r_sector);
                                indent -= 2;
                                continue;
                        }

                        update_parity = true;

                        /* map raid sector to member disk */
                        sector = raid5_compute_sector(conf, r_sector, 0,
                                                      &dd_idx, NULL);
                        pr_debug("%s:%*s processing array sector %llu => data member disk %d, sector %llu\n",
                                 __func__, indent, "",
                                 (unsigned long long)r_sector, dd_idx,
                                 (unsigned long long)sector);

                        rdev = conf->disks[dd_idx].rdev;
                        if (!rdev || (!test_bit(In_sync, &rdev->flags) &&
                                      sector >= rdev->recovery_offset)) {
                                pr_debug("%s:%*s data member disk %d missing\n",
                                         __func__, indent, "", dd_idx);
                                update_parity = false;
                                break;
                        }

                        pr_debug("%s:%*s reading data member disk %s sector %llu\n",
                                 __func__, indent, "", bdevname(rdev->bdev, b),
                                 (unsigned long long)sector);
                        if (!sync_page_io(rdev, sector, block_size, page2,
                                          READ, false)) {
                                md_error(mddev, rdev);
                                pr_debug("%s:%*s read failed!\n", __func__,
                                         indent, "");
                                ret = -EIO;
                                goto out;
                        }

                        ppl_xor(block_size, page1, page2);

                        indent -= 2;
                }

                if (!update_parity)
                        continue;

                if (pp_size > 0) {
                        pr_debug("%s:%*s reading pp disk sector %llu\n",
                                 __func__, indent, "",
                                 (unsigned long long)(ppl_sector + i));
                        if (!sync_page_io(log->rdev,
                                        ppl_sector - log->rdev->data_offset + i,
                                        block_size, page2, READ, false)) {
                                pr_debug("%s:%*s read failed!\n", __func__,
                                         indent, "");
                                md_error(mddev, log->rdev);
                                ret = -EIO;
                                goto out;
                        }

                        ppl_xor(block_size, page1, page2);
                }

                /* map raid sector to parity disk */
                parity_sector = raid5_compute_sector(conf, r_sector_first + i,
                                0, &disk, &sh);
                BUG_ON(sh.pd_idx != le32_to_cpu(e->parity_disk));
                parity_rdev = conf->disks[sh.pd_idx].rdev;

                BUG_ON(parity_rdev->bdev->bd_dev != log->rdev->bdev->bd_dev);
                pr_debug("%s:%*s write parity at sector %llu, disk %s\n",
                         __func__, indent, "",
                         (unsigned long long)parity_sector,
                         bdevname(parity_rdev->bdev, b));
                if (!sync_page_io(parity_rdev, parity_sector, block_size,
                                  page1, WRITE, false)) {
                        pr_debug("%s:%*s parity write error!\n", __func__,
                                 indent, "");
                        md_error(mddev, parity_rdev);
                        ret = -EIO;
                        goto out;
                }
        }
out:
        if (page1)
                __free_page(page1);
        if (page2)
                __free_page(page2);
        return ret;
}

static int ppl_recover(struct ppl_log *log, struct ppl_header *pplhdr,
                       sector_t offset)
{
        struct ppl_conf *ppl_conf = log->ppl_conf;
        struct md_rdev *rdev = log->rdev;
        struct mddev *mddev = rdev->mddev;
        sector_t ppl_sector = rdev->ppl.sector + offset +
                              (PPL_HEADER_SIZE >> 9);
        struct page *page;
        int i;
        int ret = 0;

        page = alloc_page(GFP_KERNEL);
        if (!page)
                return -ENOMEM;

        /* iterate through all PPL entries saved */
        for (i = 0; i < le32_to_cpu(pplhdr->entries_count); i++) {
                struct ppl_header_entry *e = &pplhdr->entries[i];
                u32 pp_size = le32_to_cpu(e->pp_size);
                sector_t sector = ppl_sector;
                int ppl_entry_sectors = pp_size >> 9;
                u32 crc, crc_stored;

                pr_debug("%s: disk: %d entry: %d ppl_sector: %llu pp_size: %u\n",
                         __func__, rdev->raid_disk, i,
                         (unsigned long long)ppl_sector, pp_size);

                crc = ~0;
                crc_stored = le32_to_cpu(e->checksum);

                /* read parial parity for this entry and calculate its checksum */
                while (pp_size) {
                        int s = pp_size > PAGE_SIZE ? PAGE_SIZE : pp_size;

                        if (!sync_page_io(rdev, sector - rdev->data_offset,
                                        s, page, READ, false)) {
                                md_error(mddev, rdev);
                                ret = -EIO;
                                goto out;
                        }

                        crc = crc32c_le(crc, page_address(page), s);

                        pp_size -= s;
                        sector += s >> 9;
                }

                crc = ~crc;

                if (crc != crc_stored) {
                        /*
                         * Don't recover this entry if the checksum does not
                         * match, but keep going and try to recover other
                         * entries.
                         */
                        pr_debug("%s: ppl entry crc does not match: stored: 0x%x calculated: 0x%x\n",
                                 __func__, crc_stored, crc);
                        ppl_conf->mismatch_count++;
                } else {
                        ret = ppl_recover_entry(log, e, ppl_sector);
                        if (ret)
                                goto out;
                        ppl_conf->recovered_entries++;
                }

                ppl_sector += ppl_entry_sectors;
        }

        /* flush the disk cache after recovery if necessary */
        ret = blkdev_issue_flush(rdev->bdev, GFP_KERNEL, NULL);
out:
        __free_page(page);
        return ret;
}

static int ppl_write_empty_header(struct ppl_log *log)
{
        struct page *page;
        struct ppl_header *pplhdr;
        struct md_rdev *rdev = log->rdev;
        int ret = 0;

        pr_debug("%s: disk: %d ppl_sector: %llu\n", __func__,
                 rdev->raid_disk, (unsigned long long)rdev->ppl.sector);

        page = alloc_page(GFP_NOIO | __GFP_ZERO);
        if (!page)
                return -ENOMEM;

        pplhdr = page_address(page);
        /* zero out PPL space to avoid collision with old PPLs */
        blkdev_issue_zeroout(rdev->bdev, rdev->ppl.sector,
                            log->rdev->ppl.size, GFP_NOIO);
        memset(pplhdr->reserved, 0xff, PPL_HDR_RESERVED);
        pplhdr->signature = cpu_to_le32(log->ppl_conf->signature);
        pplhdr->checksum = cpu_to_le32(~crc32c_le(~0, pplhdr, PAGE_SIZE));

        if (!sync_page_io(rdev, rdev->ppl.sector - rdev->data_offset,
                          PPL_HEADER_SIZE, page, WRITE_FUA, false)) {
                md_error(rdev->mddev, rdev);
                ret = -EIO;
        }

        __free_page(page);
        return ret;
}

static int ppl_load_distributed(struct ppl_log *log)
{
        struct ppl_conf *ppl_conf = log->ppl_conf;
        struct md_rdev *rdev = log->rdev;
        struct mddev *mddev = rdev->mddev;
        struct page *page, *page2, *tmp;
        struct ppl_header *pplhdr = NULL, *prev_pplhdr = NULL;
        u32 crc, crc_stored;
        u32 signature;
        int ret = 0, i;
        sector_t pplhdr_offset = 0, prev_pplhdr_offset = 0;

        pr_debug("%s: disk: %d\n", __func__, rdev->raid_disk);
        /* read PPL headers, find the recent one */
        page = alloc_page(GFP_KERNEL);
        if (!page)
                return -ENOMEM;

        page2 = alloc_page(GFP_KERNEL);
        if (!page2) {
                __free_page(page);
                return -ENOMEM;
        }

        /* searching ppl area for latest ppl */
        while (pplhdr_offset < rdev->ppl.size - (PPL_HEADER_SIZE >> 9)) {
                if (!sync_page_io(rdev,
                                  rdev->ppl.sector - rdev->data_offset +
                                  pplhdr_offset, PAGE_SIZE, page, READ,
                                  false)) {
                        md_error(mddev, rdev);
                        ret = -EIO;
                        /* if not able to read - don't recover any PPL */
                        pplhdr = NULL;
                        break;
                }
                pplhdr = page_address(page);

                /* check header validity */
                crc_stored = le32_to_cpu(pplhdr->checksum);
                pplhdr->checksum = 0;
                crc = ~crc32c_le(~0, pplhdr, PAGE_SIZE);

                if (crc_stored != crc) {
                        pr_debug("%s: ppl header crc does not match: stored: 0x%x calculated: 0x%x (offset: %llu)\n",
                                 __func__, crc_stored, crc,
                                 (unsigned long long)pplhdr_offset);
                        pplhdr = prev_pplhdr;
                        pplhdr_offset = prev_pplhdr_offset;
                        break;
                }

                signature = le32_to_cpu(pplhdr->signature);

                if (mddev->external) {
                        /*
                         * For external metadata the header signature is set and
                         * validated in userspace.
                         */
                        ppl_conf->signature = signature;
                } else if (ppl_conf->signature != signature) {
                        pr_debug("%s: ppl header signature does not match: stored: 0x%x configured: 0x%x (offset: %llu)\n",
                                 __func__, signature, ppl_conf->signature,
                                 (unsigned long long)pplhdr_offset);
                        pplhdr = prev_pplhdr;
                        pplhdr_offset = prev_pplhdr_offset;
                        break;
                }

                if (prev_pplhdr && le64_to_cpu(prev_pplhdr->generation) >
                    le64_to_cpu(pplhdr->generation)) {
                        /* previous was newest */
                        pplhdr = prev_pplhdr;
                        pplhdr_offset = prev_pplhdr_offset;
                        break;
                }

                prev_pplhdr_offset = pplhdr_offset;
                prev_pplhdr = pplhdr;

                tmp = page;
                page = page2;
                page2 = tmp;

                /* calculate next potential ppl offset */
                for (i = 0; i < le32_to_cpu(pplhdr->entries_count); i++)
                        pplhdr_offset +=
                            le32_to_cpu(pplhdr->entries[i].pp_size) >> 9;
                pplhdr_offset += PPL_HEADER_SIZE >> 9;
        }

        /* no valid ppl found */
        if (!pplhdr)
                ppl_conf->mismatch_count++;
        else
                pr_debug("%s: latest PPL found at offset: %llu, with generation: %llu\n",
                    __func__, (unsigned long long)pplhdr_offset,
                    le64_to_cpu(pplhdr->generation));

        /* attempt to recover from log if we are starting a dirty array */
        if (pplhdr && !mddev->pers && mddev->recovery_cp != MaxSector)
                ret = ppl_recover(log, pplhdr, pplhdr_offset);

        /* write empty header if we are starting the array */
        if (!ret && !mddev->pers)
                ret = ppl_write_empty_header(log);

        __free_page(page);
        __free_page(page2);

        pr_debug("%s: return: %d mismatch_count: %d recovered_entries: %d\n",
                 __func__, ret, ppl_conf->mismatch_count,
                 ppl_conf->recovered_entries);
        return ret;
}

static int ppl_load(struct ppl_conf *ppl_conf)
{
        int ret = 0;
        u32 signature = 0;
        bool signature_set = false;
        int i;

        for (i = 0; i < ppl_conf->count; i++) {
                struct ppl_log *log = &ppl_conf->child_logs[i];

                /* skip missing drive */
                if (!log->rdev)
                        continue;

                ret = ppl_load_distributed(log);
                if (ret)
                        break;

                /*
                 * For external metadata we can't check if the signature is
                 * correct on a single drive, but we can check if it is the same
                 * on all drives.
                 */
                if (ppl_conf->mddev->external) {
                        if (!signature_set) {
                                signature = ppl_conf->signature;
                                signature_set = true;
                        } else if (signature != ppl_conf->signature) {
                                pr_warn("md/raid:%s: PPL header signature does not match on all member drives\n",
                                        mdname(ppl_conf->mddev));
                                ret = -EINVAL;
                                break;
                        }
                }
        }

        pr_debug("%s: return: %d mismatch_count: %d recovered_entries: %d\n",
                 __func__, ret, ppl_conf->mismatch_count,
                 ppl_conf->recovered_entries);
        return ret;
}

static void __ppl_exit_log(struct ppl_conf *ppl_conf)
{
        clear_bit(MD_HAS_PPL, &ppl_conf->mddev->flags);
        clear_bit(MD_HAS_MULTIPLE_PPLS, &ppl_conf->mddev->flags);

        kfree(ppl_conf->child_logs);

        if (ppl_conf->bs)
                bioset_free(ppl_conf->bs);
        mempool_destroy(ppl_conf->io_pool);
        kmem_cache_destroy(ppl_conf->io_kc);

        kfree(ppl_conf);
}

void ppl_exit_log(struct r5conf *conf)
{
        struct ppl_conf *ppl_conf = conf->log_private;

        if (ppl_conf) {
                __ppl_exit_log(ppl_conf);
                conf->log_private = NULL;
        }
}

static int ppl_validate_rdev(struct md_rdev *rdev)
{
        char b[BDEVNAME_SIZE];
        int ppl_data_sectors;
        int ppl_size_new;

        /*
         * The configured PPL size must be enough to store
         * the header and (at the very least) partial parity
         * for one stripe. Round it down to ensure the data
         * space is cleanly divisible by stripe size.
         */
        ppl_data_sectors = rdev->ppl.size - (PPL_HEADER_SIZE >> 9);

        if (ppl_data_sectors > 0)
                ppl_data_sectors = rounddown(ppl_data_sectors, STRIPE_SECTORS);

        if (ppl_data_sectors <= 0) {
                pr_warn("md/raid:%s: PPL space too small on %s\n",
                        mdname(rdev->mddev), bdevname(rdev->bdev, b));
                return -ENOSPC;
        }

        ppl_size_new = ppl_data_sectors + (PPL_HEADER_SIZE >> 9);

        if ((rdev->ppl.sector < rdev->data_offset &&
             rdev->ppl.sector + ppl_size_new > rdev->data_offset) ||
            (rdev->ppl.sector >= rdev->data_offset &&
             rdev->data_offset + rdev->sectors > rdev->ppl.sector)) {
                pr_warn("md/raid:%s: PPL space overlaps with data on %s\n",
                        mdname(rdev->mddev), bdevname(rdev->bdev, b));
                return -EINVAL;
        }

        if (!rdev->mddev->external &&
            ((rdev->ppl.offset > 0 && rdev->ppl.offset < (rdev->sb_size >> 9)) ||
             (rdev->ppl.offset <= 0 && rdev->ppl.offset + ppl_size_new > 0))) {
                pr_warn("md/raid:%s: PPL space overlaps with superblock on %s\n",
                        mdname(rdev->mddev), bdevname(rdev->bdev, b));
                return -EINVAL;
        }

        rdev->ppl.size = ppl_size_new;

        return 0;
}

static void ppl_init_child_log(struct ppl_log *log, struct md_rdev *rdev)
{
        if ((rdev->ppl.size << 9) >= (PPL_SPACE_SIZE +
                                      PPL_HEADER_SIZE) * 2) {
                log->use_multippl = true;
                set_bit(MD_HAS_MULTIPLE_PPLS,
                        &log->ppl_conf->mddev->flags);
                log->entry_space = PPL_SPACE_SIZE;
        } else {
                log->use_multippl = false;
                log->entry_space = (log->rdev->ppl.size << 9) -
                                   PPL_HEADER_SIZE;
        }
        log->next_io_sector = rdev->ppl.sector;
}

int ppl_init_log(struct r5conf *conf)
{
        struct ppl_conf *ppl_conf;
        struct mddev *mddev = conf->mddev;
        int ret = 0;
        int i;
        bool need_cache_flush = false;

        pr_debug("md/raid:%s: enabling distributed Partial Parity Log\n",
                 mdname(conf->mddev));

        if (PAGE_SIZE != 4096)
                return -EINVAL;

        if (mddev->level != 5) {
                pr_warn("md/raid:%s PPL is not compatible with raid level %d\n",
                        mdname(mddev), mddev->level);
                return -EINVAL;
        }

        if (mddev->bitmap_info.file || mddev->bitmap_info.offset) {
                pr_warn("md/raid:%s PPL is not compatible with bitmap\n",
                        mdname(mddev));
                return -EINVAL;
        }

        if (test_bit(MD_HAS_JOURNAL, &mddev->flags)) {
                pr_warn("md/raid:%s PPL is not compatible with journal\n",
                        mdname(mddev));
                return -EINVAL;
        }

        ppl_conf = kzalloc(sizeof(struct ppl_conf), GFP_KERNEL);
        if (!ppl_conf)
                return -ENOMEM;

        ppl_conf->mddev = mddev;

        ppl_conf->io_kc = KMEM_CACHE(ppl_io_unit, 0);
        if (!ppl_conf->io_kc) {
                ret = -ENOMEM;
                goto err;
        }

        ppl_conf->io_pool = mempool_create(conf->raid_disks, ppl_io_pool_alloc,
                                           ppl_io_pool_free, ppl_conf->io_kc);
        if (!ppl_conf->io_pool) {
                ret = -ENOMEM;
                goto err;
        }

        ppl_conf->bs = bioset_create(conf->raid_disks, 0);
        if (!ppl_conf->bs) {
                ret = -ENOMEM;
                goto err;
        }

        ppl_conf->count = conf->raid_disks;
        ppl_conf->child_logs = kcalloc(ppl_conf->count, sizeof(struct ppl_log),
                                       GFP_KERNEL);
        if (!ppl_conf->child_logs) {
                ret = -ENOMEM;
                goto err;
        }

        atomic64_set(&ppl_conf->seq, 0);
        INIT_LIST_HEAD(&ppl_conf->no_mem_stripes);
        spin_lock_init(&ppl_conf->no_mem_stripes_lock);

        if (!mddev->external) {
                ppl_conf->signature = ~crc32c_le(~0, mddev->uuid, sizeof(mddev->uuid));
                ppl_conf->block_size = 512;
        } else {
                ppl_conf->block_size = queue_logical_block_size(mddev->queue);
        }

        for (i = 0; i < ppl_conf->count; i++) {
                struct ppl_log *log = &ppl_conf->child_logs[i];
                struct md_rdev *rdev = conf->disks[i].rdev;

                mutex_init(&log->io_mutex);
                spin_lock_init(&log->io_list_lock);
                INIT_LIST_HEAD(&log->io_list);

                log->ppl_conf = ppl_conf;
                log->rdev = rdev;

                if (rdev) {
                        struct request_queue *q;

                        ret = ppl_validate_rdev(rdev);
                        if (ret)
                                goto err;

                        q = bdev_get_queue(rdev->bdev);
                        if (q->flush_flags)
                                need_cache_flush = true;
                        ppl_init_child_log(log, rdev);
                }
        }

        if (need_cache_flush)
                pr_warn("md/raid:%s: Volatile write-back cache should be disabled on all member drives when using PPL!\n",
                        mdname(mddev));

        /* load and possibly recover the logs from the member disks */
        ret = ppl_load(ppl_conf);

        if (ret) {
                goto err;
        } else if (!mddev->pers && mddev->recovery_cp == 0 &&
                   ppl_conf->recovered_entries > 0 &&
                   ppl_conf->mismatch_count == 0) {
                /*
                 * If we are starting a dirty array and the recovery succeeds
                 * without any issues, set the array as clean.
                 */
                mddev->recovery_cp = MaxSector;
                set_bit(MD_SB_CHANGE_CLEAN, &mddev->flags);
        } else if (mddev->pers && ppl_conf->mismatch_count > 0) {
                /* no mismatch allowed when enabling PPL for a running array */
                ret = -EINVAL;
                goto err;
        }

        conf->log_private = ppl_conf;
        set_bit(MD_HAS_PPL, &ppl_conf->mddev->flags);

        return 0;
err:
        __ppl_exit_log(ppl_conf);
        return ret;
}

int ppl_modify_log(struct r5conf *conf, struct md_rdev *rdev, bool add)
{
        struct ppl_conf *ppl_conf = conf->log_private;
        struct ppl_log *log;
        int ret = 0;
        char b[BDEVNAME_SIZE];

        if (!rdev)
                return -EINVAL;

        pr_debug("%s: disk: %d operation: %s dev: %s\n",
                 __func__, rdev->raid_disk, add ? "add" : "remove",
                 bdevname(rdev->bdev, b));

        if (rdev->raid_disk < 0)
                return 0;

        if (rdev->raid_disk >= ppl_conf->count)
                return -ENODEV;

        log = &ppl_conf->child_logs[rdev->raid_disk];

        mutex_lock(&log->io_mutex);
        if (add) {
                ret = ppl_validate_rdev(rdev);
                if (!ret) {
                        log->rdev = rdev;
                        ret = ppl_write_empty_header(log);
                        ppl_init_child_log(log, rdev);
                }
        } else {
                log->rdev = NULL;
        }
        mutex_unlock(&log->io_mutex);

        return ret;
}