Method preadv

fs/cache/persistent_cache/persistent_cache.cpp:167–239

}

ssize_t PersistentCacheFile::preadv(const struct iovec *iov, int iovcnt, off_t offset) {
    ssize_t ret = 0;
    if (!ready) {
        LOG_WARN("local path or size not set, read from source ", VALUE(offset));
        SCOPE_AUDIT("download", AU_FILEOP(m_name, offset, ret));
        ret = m_file->preadv(iov, iovcnt, offset);
        return ret;
    }

    iovector_view view((iovec *)iov, iovcnt);
    size_t count = view.sum();
    if (count == 0) {
        return 0;
    }

    std::pair<off_t, size_t> q;

    off_t align_left = align_down(offset, m_fs->block_size);
    off_t align_right = align_up(offset + count, m_fs->block_size);

again:

     m_local_file->lock(align_left, align_right - align_left);
    {
        DEFER({m_local_file->unlock(align_left, align_right - align_left);});
        q = m_local_file->query_refill_range(offset, count);
        if (q.second == 0) { // no need to refill
            return m_local_file->preadv(iov, iovcnt, offset);
        }
    }

    // refill
    uint64_t r_offset = q.first;
    uint64_t r_count = q.second;
    if (r_offset + r_count > m_size) {
        r_count = m_size - r_offset;
    }

    IOVector buffer(*m_fs->io_alloc);

    auto lr = m_local_file->try_lock_wait(r_offset, r_count);
    if (lr < 0) {
        goto again;
    }
    DEFER({ m_local_file->unlock(r_offset, r_count); });

    auto alloc = buffer.push_back(r_count);
    if (alloc < r_count) {
        LOG_ERROR("memory allocate failed, refill size:`, alloc:`", r_count, alloc);
        SCOPE_AUDIT("download", AU_FILEOP(m_name, offset, ret));
        ret = m_file->preadv(iov, iovcnt, offset);
        return ret;
    }

    ssize_t read = 0;
    {
        SCOPE_AUDIT("download", AU_FILEOP(m_name, r_offset, read));
        read = m_file->preadv(buffer.iovec(), buffer.iovcnt(), r_offset);