Function bcache_write_partial

src/blockcache.cc:1147–1243

}

int bcache_write_partial(struct filemgr *file,
                         bid_t bid,
                         void *buf,
                         size_t offset,
                         size_t len,
                         bool final_write)
{
    struct hash_elem *h;
    struct bcache_item *item;
    struct bcache_item query;
    struct fnamedic_item *fname_new;

    fname_new = file->bcache;
    if (fname_new == NULL) {
        spin_lock(&bcache_lock);
        fname_new = file->bcache;
        if (fname_new == NULL) {
            // filename doesn't exist in filename dictionary .. create
            fname_new = _fname_create(file);
        }
        spin_unlock(&bcache_lock);
    }

    // Update the access timestamp.
    struct timeval tp;
    gettimeofday(&tp, NULL);
    atomic_store_uint64_t(&fname_new->access_timestamp,
                          (uint64_t) (tp.tv_sec * 1000000 + tp.tv_usec));

    size_t shard_num = bid % fname_new->num_shards;
    // set query
    query.bid = bid;

    spin_lock(&fname_new->shards[shard_num].lock);

    // search hash table
    h = hash_find(&fname_new->shards[shard_num].hashtable, &query.hash_elem);
    if (h == NULL) {
        // cache miss .. partial write fail .. return 0
        spin_unlock(&fname_new->shards[shard_num].lock);
        return 0;

    } else {
        // cache hit .. get the block
        item = _get_entry(h, struct bcache_item, hash_elem);
    }

    if (item->flag & BCACHE_FREE) {
        DBG("Warning: failed to write on the buffer cache entry for a file '%s' "
            "because the entry belongs to the free list!\n",
            file->filename);
        return 0;
    }

    // check whether this is dirty block
    // to avoid re-insert already existing item into tree
    if (!(item->flag & BCACHE_DIRTY)) {
        // this block was clean block