// SPDX-License-Identifier: GPL-2.0-or-later
/* Rolling buffer helpers
 *
 * Copyright (C) 2024 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/bitops.h>
#include <linux/pagemap.h>
#include <linux/rolling_buffer.h>
#include <linux/slab.h>
#include "internal.h"

static atomic_t debug_ids;

/**
 * netfs_folioq_alloc - Allocate a folio_queue struct
 * @rreq_id: Associated debugging ID for tracing purposes
 * @gfp: Allocation constraints
 * @trace: Trace tag to indicate the purpose of the allocation
 *
 * Allocate, initialise and account the folio_queue struct and log a trace line
 * to mark the allocation.
 */
struct folio_queue *netfs_folioq_alloc(unsigned int rreq_id, gfp_t gfp,
                                       unsigned int /*enum netfs_folioq_trace*/ trace)
{
        struct folio_queue *fq;

        fq = kmalloc_obj(*fq, gfp);
        if (fq) {
                netfs_stat(&netfs_n_folioq);
                folioq_init(fq, rreq_id);
                fq->debug_id = atomic_inc_return(&debug_ids);
                trace_netfs_folioq(fq, trace);
        }
        return fq;
}
EXPORT_SYMBOL(netfs_folioq_alloc);

/**
 * netfs_folioq_free - Free a folio_queue struct
 * @folioq: The object to free
 * @trace: Trace tag to indicate which free
 *
 * Free and unaccount the folio_queue struct.
 */
void netfs_folioq_free(struct folio_queue *folioq,
                       unsigned int /*enum netfs_trace_folioq*/ trace)
{
        trace_netfs_folioq(folioq, trace);
        netfs_stat_d(&netfs_n_folioq);
        kfree(folioq);
}
EXPORT_SYMBOL(netfs_folioq_free);

/*
 * Initialise a rolling buffer.  We allocate an empty folio queue struct to so
 * that the pointers can be independently driven by the producer and the
 * consumer.
 */
int rolling_buffer_init(struct rolling_buffer *roll, unsigned int rreq_id,
                        unsigned int direction)
{
        struct folio_queue *fq;

        fq = netfs_folioq_alloc(rreq_id, GFP_NOFS, netfs_trace_folioq_rollbuf_init);
        if (!fq)
                return -ENOMEM;

        roll->head = fq;
        roll->tail = fq;
        iov_iter_folio_queue(&roll->iter, direction, fq, 0, 0, 0);
        return 0;
}

/*
 * Add another folio_queue to a rolling buffer if there's no space left.
 */
int rolling_buffer_make_space(struct rolling_buffer *roll)
{
        struct folio_queue *fq, *head = roll->head;

        if (!folioq_full(head))
                return 0;

        fq = netfs_folioq_alloc(head->rreq_id, GFP_NOFS, netfs_trace_folioq_make_space);
        if (!fq)
                return -ENOMEM;
        fq->prev = head;

        roll->head = fq;
        if (folioq_full(head)) {
                /* Make sure we don't leave the master iterator pointing to a
                 * block that might get immediately consumed.
                 */
                if (roll->iter.folioq == head &&
                    roll->iter.folioq_slot == folioq_nr_slots(head)) {
                        roll->iter.folioq = fq;
                        roll->iter.folioq_slot = 0;
                }
        }

        /* Make sure the initialisation is stored before the next pointer.
         *
         * [!] NOTE: After we set head->next, the consumer is at liberty to
         * immediately delete the old head.
         */
        smp_store_release(&head->next, fq);
        return 0;
}

/*
 * Decant the list of folios to read into a rolling buffer.
 */
ssize_t rolling_buffer_load_from_ra(struct rolling_buffer *roll,
                                    struct readahead_control *ractl,
                                    struct folio_batch *put_batch)
{
        struct folio_queue *fq;
        struct page **vec;
        int nr, ix, to;
        ssize_t size = 0;

        if (rolling_buffer_make_space(roll) < 0)
                return -ENOMEM;

        fq = roll->head;
        vec = (struct page **)fq->vec.folios;
        nr = __readahead_batch(ractl, vec + folio_batch_count(&fq->vec),
                               folio_batch_space(&fq->vec));
        ix = fq->vec.nr;
        to = ix + nr;
        fq->vec.nr = to;
        for (; ix < to; ix++) {
                struct folio *folio = folioq_folio(fq, ix);
                unsigned int order = folio_order(folio);

                fq->orders[ix] = order;
                size += PAGE_SIZE << order;
                trace_netfs_folio(folio, netfs_folio_trace_read);
                if (!folio_batch_add(put_batch, folio))
                        folio_batch_release(put_batch);
        }
        WRITE_ONCE(roll->iter.count, roll->iter.count + size);

        /* Store the counter after setting the slot. */
        smp_store_release(&roll->next_head_slot, to);
        return size;
}

/*
 * Append a folio to the rolling buffer.
 */
ssize_t rolling_buffer_append(struct rolling_buffer *roll, struct folio *folio,
                              unsigned int flags)
{
        ssize_t size = folio_size(folio);
        int slot;

        if (rolling_buffer_make_space(roll) < 0)
                return -ENOMEM;

        slot = folioq_append(roll->head, folio);
        if (flags & ROLLBUF_MARK_1)
                folioq_mark(roll->head, slot);
        if (flags & ROLLBUF_MARK_2)
                folioq_mark2(roll->head, slot);

        WRITE_ONCE(roll->iter.count, roll->iter.count + size);

        /* Store the counter after setting the slot. */
        smp_store_release(&roll->next_head_slot, slot);
        return size;
}

/*
 * Delete a spent buffer from a rolling queue and return the next in line.  We
 * don't return the last buffer to keep the pointers independent, but return
 * NULL instead.
 */
struct folio_queue *rolling_buffer_delete_spent(struct rolling_buffer *roll)
{
        struct folio_queue *spent = roll->tail, *next = READ_ONCE(spent->next);

        if (!next)
                return NULL;
        next->prev = NULL;
        netfs_folioq_free(spent, netfs_trace_folioq_delete);
        roll->tail = next;
        return next;
}

/*
 * Clear out a rolling queue.  Folios that have mark 1 set are put.
 */
void rolling_buffer_clear(struct rolling_buffer *roll)
{
        struct folio_batch fbatch;
        struct folio_queue *p;

        folio_batch_init(&fbatch);

        while ((p = roll->tail)) {
                roll->tail = p->next;
                for (int slot = 0; slot < folioq_count(p); slot++) {
                        struct folio *folio = folioq_folio(p, slot);

                        if (!folio)
                                continue;
                        if (folioq_is_marked(p, slot)) {
                                trace_netfs_folio(folio, netfs_folio_trace_put);
                                if (!folio_batch_add(&fbatch, folio))
                                        folio_batch_release(&fbatch);
                        }
                }

                netfs_folioq_free(p, netfs_trace_folioq_clear);
        }

        folio_batch_release(&fbatch);
}