// SPDX-License-Identifier: GPL-2.0-or-later
#include "cache.h"
#include "backing_dev.h"
#include "cache_dev.h"
#include "dm_pcache.h"

/**
 * cache_key_gc - Releases the reference of a cache key segment.
 * @cache: Pointer to the pcache_cache structure.
 * @key: Pointer to the cache key to be garbage collected.
 *
 * This function decrements the reference count of the cache segment
 * associated with the given key. If the reference count drops to zero,
 * the segment may be invalidated and reused.
 */
static void cache_key_gc(struct pcache_cache *cache, struct pcache_cache_key *key)
{
        cache_seg_put(key->cache_pos.cache_seg);
}

static bool need_gc(struct pcache_cache *cache, struct pcache_cache_pos *dirty_tail, struct pcache_cache_pos *key_tail)
{
        struct dm_pcache *pcache = CACHE_TO_PCACHE(cache);
        struct pcache_cache_kset_onmedia *kset_onmedia;
        void *dirty_addr, *key_addr;
        u32 segs_used, segs_gc_threshold, to_copy;
        int ret;

        dirty_addr = cache_pos_addr(dirty_tail);
        key_addr = cache_pos_addr(key_tail);
        if (dirty_addr == key_addr) {
                pcache_dev_debug(pcache, "key tail is equal to dirty tail: %u:%u\n",
                                dirty_tail->cache_seg->cache_seg_id,
                                dirty_tail->seg_off);
                return false;
        }

        kset_onmedia = (struct pcache_cache_kset_onmedia *)cache->gc_kset_onmedia_buf;

        to_copy = min(PCACHE_KSET_ONMEDIA_SIZE_MAX, PCACHE_SEG_SIZE - key_tail->seg_off);
        ret = copy_mc_to_kernel(kset_onmedia, key_addr, to_copy);
        if (ret) {
                pcache_dev_err(pcache, "error to read kset: %d", ret);
                return false;
        }

        /* Check if kset_onmedia is corrupted */
        if (kset_onmedia->magic != PCACHE_KSET_MAGIC) {
                pcache_dev_debug(pcache, "gc error: magic is not as expected. key_tail: %u:%u magic: %llx, expected: %llx\n",
                                        key_tail->cache_seg->cache_seg_id, key_tail->seg_off,
                                        kset_onmedia->magic, PCACHE_KSET_MAGIC);
                return false;
        }

        /* Verify the CRC of the kset_onmedia */
        if (kset_onmedia->crc != cache_kset_crc(kset_onmedia)) {
                pcache_dev_debug(pcache, "gc error: crc is not as expected. crc: %x, expected: %x\n",
                                        cache_kset_crc(kset_onmedia), kset_onmedia->crc);
                return false;
        }

        segs_used = bitmap_weight(cache->seg_map, cache->n_segs);
        segs_gc_threshold = cache->n_segs * pcache_cache_get_gc_percent(cache) / 100;
        if (segs_used < segs_gc_threshold) {
                pcache_dev_debug(pcache, "segs_used: %u, segs_gc_threshold: %u\n", segs_used, segs_gc_threshold);
                return false;
        }

        return true;
}

/**
 * last_kset_gc - Advances the garbage collection for the last kset.
 * @cache: Pointer to the pcache_cache structure.
 * @kset_onmedia: Pointer to the kset_onmedia structure for the last kset.
 */
static void last_kset_gc(struct pcache_cache *cache, struct pcache_cache_kset_onmedia *kset_onmedia)
{
        struct dm_pcache *pcache = CACHE_TO_PCACHE(cache);
        struct pcache_cache_segment *cur_seg, *next_seg;

        cur_seg = cache->key_tail.cache_seg;

        next_seg = &cache->segments[kset_onmedia->next_cache_seg_id];

        mutex_lock(&cache->key_tail_lock);
        cache->key_tail.cache_seg = next_seg;
        cache->key_tail.seg_off = 0;
        cache_encode_key_tail(cache);
        mutex_unlock(&cache->key_tail_lock);

        pcache_dev_debug(pcache, "gc advance kset seg: %u\n", cur_seg->cache_seg_id);

        spin_lock(&cache->seg_map_lock);
        __clear_bit(cur_seg->cache_seg_id, cache->seg_map);
        spin_unlock(&cache->seg_map_lock);
}

void pcache_cache_gc_fn(struct work_struct *work)
{
        struct pcache_cache *cache = container_of(work, struct pcache_cache, gc_work.work);
        struct dm_pcache *pcache = CACHE_TO_PCACHE(cache);
        struct pcache_cache_pos dirty_tail, key_tail;
        struct pcache_cache_kset_onmedia *kset_onmedia;
        struct pcache_cache_key_onmedia *key_onmedia;
        struct pcache_cache_key *key;
        int ret;
        int i;

        kset_onmedia = (struct pcache_cache_kset_onmedia *)cache->gc_kset_onmedia_buf;

        while (true) {
                if (pcache_is_stopping(pcache) || atomic_read(&cache->gc_errors))
                        return;

                /* Get new tail positions */
                mutex_lock(&cache->dirty_tail_lock);
                cache_pos_copy(&dirty_tail, &cache->dirty_tail);
                mutex_unlock(&cache->dirty_tail_lock);

                mutex_lock(&cache->key_tail_lock);
                cache_pos_copy(&key_tail, &cache->key_tail);
                mutex_unlock(&cache->key_tail_lock);

                if (!need_gc(cache, &dirty_tail, &key_tail))
                        break;

                if (kset_onmedia->flags & PCACHE_KSET_FLAGS_LAST) {
                        /* Don't move to the next segment if dirty_tail has not moved */
                        if (dirty_tail.cache_seg == key_tail.cache_seg)
                                break;

                        last_kset_gc(cache, kset_onmedia);
                        continue;
                }

                for (i = 0; i < kset_onmedia->key_num; i++) {
                        struct pcache_cache_key key_tmp = { 0 };

                        key_onmedia = &kset_onmedia->data[i];

                        key = &key_tmp;
                        cache_key_init(&cache->req_key_tree, key);

                        ret = cache_key_decode(cache, key_onmedia, key);
                        if (ret) {
                                /* return without re-arm gc work, and prevent future
                                 * gc, because we can't retry the partial-gc-ed kset
                                 */
                                atomic_inc(&cache->gc_errors);
                                pcache_dev_err(pcache, "failed to decode cache key in gc\n");
                                return;
                        }

                        cache_key_gc(cache, key);
                }

                pcache_dev_debug(pcache, "gc advance: %u:%u %u\n",
                        key_tail.cache_seg->cache_seg_id,
                        key_tail.seg_off,
                        get_kset_onmedia_size(kset_onmedia));

                mutex_lock(&cache->key_tail_lock);
                cache_pos_advance(&cache->key_tail, get_kset_onmedia_size(kset_onmedia));
                cache_encode_key_tail(cache);
                mutex_unlock(&cache->key_tail_lock);
        }

        queue_delayed_work(cache_get_wq(cache), &cache->gc_work, PCACHE_CACHE_GC_INTERVAL);
}