vitastor/blockstore_write.cpp

#include "blockstore.h"

void blockstore::enqueue_write(blockstore_operation *op)
{
    // Assign version number
    auto dirty_it = dirty_db.upper_bound((obj_ver_id){
        .oid = op->oid,
        .version = UINT64_MAX,
    });
    dirty_it--;
    if (dirty_it != dirty_db.end() && dirty_it->first.oid == op->oid)
    {
        op->version = dirty_it->first.version + 1;
    }
    else
    {
        auto clean_it = object_db.find(op->oid);
        if (clean_it != object_db.end())
        {
            op->version = clean_it->second.version + 1;
        }
        else
        {
            op->version = 1;
        }
    }
    // Immediately add the operation into dirty_db, so subsequent reads could see it
    dirty_db.emplace((obj_ver_id){
        .oid = op->oid,
        .version = op->version,
    }, (dirty_entry){
        .state = ST_IN_FLIGHT,
        .flags = 0,
        .location = 0,
        .offset = op->offset,
        .size = op->len,
    });
}

// First step of the write algorithm: dequeue operation and submit initial write(s)
int blockstore::dequeue_write(blockstore_operation *op)
{
    auto dirty_it = dirty_db.find((obj_ver_id){
        .oid = op->oid,
        .version = op->version,
    });
    if (op->len == block_size)
    {
        // Big (redirect) write
        uint64_t loc = allocator_find_free(data_alloc);
        if (loc == (uint64_t)-1)
        {
            // no space
            op->retval = -ENOSPC;
            op->callback(op);
            return 1;
        }
        BS_SUBMIT_GET_SQE(sqe, data);
        dirty_it->second.location = loc << block_order;
        dirty_it->second.state = ST_D_SUBMITTED;
        allocator_set(data_alloc, loc, true);
        data->iov = (struct iovec){ op->buf, op->len };
        data->op = op;
        io_uring_prep_writev(
            sqe, data_fd, &data->iov, 1, data_offset + (loc << block_order)
        );
        op->pending_ops = 1;
        op->min_used_journal_sector = op->max_used_journal_sector = 0;
    }
    else
    {
        // Small (journaled) write
        // First check if the journal has sufficient space
        // FIXME Always two SQEs for now. Although it's possible to send 1 sometimes
        uint64_t next_pos = journal.next_free;
        if (512 - journal.in_sector_pos < sizeof(struct journal_entry_small_write))
        {
            //if (journal.len - next_pos < op->len)
            //    two_sqes = true;
            next_pos = (next_pos+512) < journal.len ? next_pos+512 : 512;
            // Also check if we have an unused memory buffer for the journal sector
            if (journal.sector_info[((journal.cur_sector + 1) % journal.sector_count)].usage_count > 0)
            {
                // No memory buffer available. Wait for it.
                op->wait_for = WAIT_JOURNAL_BUFFER;
                return 0;
            }
        }
        //else if (journal.sector_info[journal.cur_sector].offset + 512 != journal.next_free ||
        //    journal.len - next_pos < op->len)
        //    two_sqes = true;
        next_pos = (journal.len - next_pos < op->len ? 512 : next_pos) + op->len;
        if (next_pos >= journal.used_start)
        {
            // No space in the journal. Wait for it.
            op->wait_for = WAIT_JOURNAL;
            op->wait_detail = next_pos;
            return 0;
        }
        // There is sufficient space. Get SQE(s)
        BS_SUBMIT_GET_SQE(sqe1, data1);
        BS_SUBMIT_GET_SQE(sqe2, data2);
        // Got SQEs. Prepare journal sector write
        if (512 - journal.in_sector_pos < sizeof(struct journal_entry_small_write))
        {
            // Move to the next journal sector
            // Also select next sector buffer in memory
            journal.cur_sector = ((journal.cur_sector + 1) % journal.sector_count);
            journal.sector_info[journal.cur_sector].offset = journal.next_free;
            journal.in_sector_pos = 0;
            journal.next_free = (journal.next_free+512) < journal.len ? journal.next_free + 512 : 512;
            memset(journal.sector_buf + 512*journal.cur_sector, 0, 512);
        }
        journal_entry_small_write *je = (struct journal_entry_small_write*)(
            journal.sector_buf + 512*journal.cur_sector + journal.in_sector_pos
        );
        *je = {
            .crc32 = 0,
            .magic = JOURNAL_MAGIC,
            .type = JE_SMALL_WRITE,
            .size = sizeof(struct journal_entry_small_write),
            .crc32_prev = journal.crc32_last,
            .oid = op->oid,
            .version = op->version,
            .offset = op->offset,
            .len = op->len,
        };
        je->crc32 = je_crc32((journal_entry*)je);
        journal.crc32_last = je->crc32;
        data1->iov = (struct iovec){ journal.sector_buf + 512*journal.cur_sector, 512 };
        data1->op = op;
        io_uring_prep_writev(
            sqe1, journal.fd, &data1->iov, 1, journal.offset + journal.sector_info[journal.cur_sector].offset
        );
        journal.sector_info[journal.cur_sector].usage_count++;
        // Prepare journal data write
        journal.next_free = (journal.next_free + op->len) < journal.len ? journal.next_free + op->len : 512;
        data2->iov = (struct iovec){ op->buf, op->len };
        data2->op = op;
        io_uring_prep_writev(
            sqe2, journal.fd, &data2->iov, 1, journal.offset + journal.next_free
        );
        dirty_it->second.location = journal.next_free;
        dirty_it->second.state = ST_J_SUBMITTED;
        // Move journal.next_free
        journal.next_free += op->len;
        op->pending_ops = 2;
        op->min_used_journal_sector = op->max_used_journal_sector = 1 + journal.cur_sector;
    }
    return 1;
}

void blockstore::handle_write_event(ring_data_t *data, blockstore_operation *op)
{
    if (data->res < 0)
    {
        // write error
        // FIXME: our state becomes corrupted after a write error. maybe do something better than just die
        throw new std::runtime_error("write operation failed. in-memory state is corrupted. AAAAAAAaaaaaaaaa!!!111");
    }
    op->pending_ops--;
    if (op->pending_ops == 0)
    {
        // Release used journal sectors
        if (op->min_used_journal_sector > 0)
        {
            for (uint64_t s = op->min_used_journal_sector; s <= op->max_used_journal_sector; s++)
            {
                journal.sector_info[s-1].usage_count--;
            }
            op->min_used_journal_sector = op->max_used_journal_sector = 0;
        }
        // Switch object state
        auto & dirty_entry = dirty_db[(obj_ver_id){
            .oid = op->oid,
            .version = op->version,
        }];
        if (dirty_entry.state == ST_J_SUBMITTED)
        {
            dirty_entry.state = ST_J_WRITTEN;
        }
        else if (dirty_entry.state == ST_D_SUBMITTED)
        {
            dirty_entry.state = ST_D_WRITTEN;
        }
        else if (dirty_entry.state == ST_DEL_SUBMITTED)
        {
            dirty_entry.state = ST_DEL_WRITTEN;
        }
        // Acknowledge write without sync
        op->retval = op->len;
        op->callback(op);
        // Remember write as unsynced
        // FIXME: Could state change to ST_STABLE? It could break this check
        if (IS_BIG_WRITE(dirty_entry.state))
        {
            unsynced_big_writes.push_back((obj_ver_id){
                .oid = op->oid,
                .version = op->version,
            });
        }
        else
        {
            unsynced_small_writes.push_back((obj_ver_id){
                .oid = op->oid,
                .version = op->version,
            });
        }
    }
}