Simplified distributed block storage with strong consistency, like in Ceph
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#include "blockstore_impl.h"
#define SYNC_HAS_SMALL 1
#define SYNC_HAS_BIG 2
#define SYNC_DATA_SYNC_SENT 3
#define SYNC_DATA_SYNC_DONE 4
#define SYNC_JOURNAL_WRITE_SENT 5
#define SYNC_JOURNAL_WRITE_DONE 6
#define SYNC_JOURNAL_SYNC_SENT 7
#define SYNC_DONE 8
int blockstore_impl_t::dequeue_sync(blockstore_op_t *op)
{
if (PRIV(op)->sync_state == 0)
{
stop_sync_submitted = false;
PRIV(op)->sync_big_writes.swap(unsynced_big_writes);
PRIV(op)->sync_small_writes.swap(unsynced_small_writes);
PRIV(op)->sync_small_checked = 0;
PRIV(op)->sync_big_checked = 0;
unsynced_big_writes.clear();
unsynced_small_writes.clear();
if (PRIV(op)->sync_big_writes.size() > 0)
PRIV(op)->sync_state = SYNC_HAS_BIG;
else if (PRIV(op)->sync_small_writes.size() > 0)
PRIV(op)->sync_state = SYNC_HAS_SMALL;
else
PRIV(op)->sync_state = SYNC_DONE;
// Always add sync to in_progress_syncs because we clear unsynced_big_writes and unsynced_small_writes
PRIV(op)->prev_sync_count = in_progress_syncs.size();
PRIV(op)->in_progress_ptr = in_progress_syncs.insert(in_progress_syncs.end(), op);
}
continue_sync(op);
// Always dequeue because we always add syncs to in_progress_syncs
return 1;
}
int blockstore_impl_t::continue_sync(blockstore_op_t *op)
{
auto cb = [this, op](ring_data_t *data) { handle_sync_event(data, op); };
if (PRIV(op)->sync_state == SYNC_HAS_SMALL)
{
// No big writes, just fsync the journal
for (; PRIV(op)->sync_small_checked < PRIV(op)->sync_small_writes.size(); PRIV(op)->sync_small_checked++)
{
if (IS_IN_FLIGHT(dirty_db[PRIV(op)->sync_small_writes[PRIV(op)->sync_small_checked]].state))
{
// Wait for small inflight writes to complete
return 0;
}
}
if (journal.sector_info[journal.cur_sector].dirty)
{
// Write out the last journal sector if it happens to be dirty
BS_SUBMIT_GET_ONLY_SQE(sqe);
prepare_journal_sector_write(journal, journal.cur_sector, sqe, cb);
PRIV(op)->min_used_journal_sector = PRIV(op)->max_used_journal_sector = 1 + journal.cur_sector;
PRIV(op)->pending_ops = 1;
PRIV(op)->sync_state = SYNC_JOURNAL_WRITE_SENT;
return 1;
}
else
{
PRIV(op)->sync_state = SYNC_JOURNAL_WRITE_DONE;
}
}
if (PRIV(op)->sync_state == SYNC_HAS_BIG)
{
for (; PRIV(op)->sync_big_checked < PRIV(op)->sync_big_writes.size(); PRIV(op)->sync_big_checked++)
{
if (IS_IN_FLIGHT(dirty_db[PRIV(op)->sync_big_writes[PRIV(op)->sync_big_checked]].state))
{
// Wait for big inflight writes to complete
return 0;
}
}
// 1st step: fsync data
if (!disable_data_fsync)
{
BS_SUBMIT_GET_SQE(sqe, data);
my_uring_prep_fsync(sqe, data_fd_index, IORING_FSYNC_DATASYNC);
sqe->flags |= IOSQE_FIXED_FILE;
data->iov = { 0 };
data->callback = cb;
PRIV(op)->min_used_journal_sector = PRIV(op)->max_used_journal_sector = 0;
PRIV(op)->pending_ops = 1;
PRIV(op)->sync_state = SYNC_DATA_SYNC_SENT;
return 1;
}
else
{
PRIV(op)->sync_state = SYNC_DATA_SYNC_DONE;
}
}
if (PRIV(op)->sync_state == SYNC_DATA_SYNC_DONE)
{
for (; PRIV(op)->sync_small_checked < PRIV(op)->sync_small_writes.size(); PRIV(op)->sync_small_checked++)
{
if (IS_IN_FLIGHT(dirty_db[PRIV(op)->sync_small_writes[PRIV(op)->sync_small_checked]].state))
{
// Wait for small inflight writes to complete
return 0;
}
}
// 2nd step: Data device is synced, prepare & write journal entries
// Check space in the journal and journal memory buffers
blockstore_journal_check_t space_check(this);
if (!space_check.check_available(op, PRIV(op)->sync_big_writes.size(), sizeof(journal_entry_big_write), 0))
{
return 0;
}
// Get SQEs. Don't bother about merging, submit each journal sector as a separate request
struct io_uring_sqe *sqe[space_check.sectors_required];
for (int i = 0; i < space_check.sectors_required; i++)
{
BS_SUBMIT_GET_SQE_DECL(sqe[i]);
}
// Prepare and submit journal entries
auto it = PRIV(op)->sync_big_writes.begin();
int s = 0, cur_sector = -1;
if ((journal_block_size - journal.in_sector_pos) < sizeof(journal_entry_big_write) &&
journal.sector_info[journal.cur_sector].dirty)
{
if (cur_sector == -1)
PRIV(op)->min_used_journal_sector = 1 + journal.cur_sector;
cur_sector = journal.cur_sector;
prepare_journal_sector_write(journal, cur_sector, sqe[s++], cb);
}
while (it != PRIV(op)->sync_big_writes.end())
{
journal_entry_big_write *je = (journal_entry_big_write*)
prefill_single_journal_entry(journal, JE_BIG_WRITE, sizeof(journal_entry_big_write));
dirty_db[*it].journal_sector = journal.sector_info[journal.cur_sector].offset;
journal.sector_info[journal.cur_sector].dirty = false;
journal.used_sectors[journal.sector_info[journal.cur_sector].offset]++;
#ifdef BLOCKSTORE_DEBUG
printf("journal offset %lu is used by %lu:%lu v%lu\n", dirty_db[*it].journal_sector, it->oid.inode, it->oid.stripe, it->version);
#endif
je->oid = it->oid;
je->version = it->version;
je->offset = dirty_db[*it].offset;
je->len = dirty_db[*it].len;
je->location = dirty_db[*it].location;
je->crc32 = je_crc32((journal_entry*)je);
journal.crc32_last = je->crc32;
it++;
if (cur_sector != journal.cur_sector)
{
if (cur_sector == -1)
PRIV(op)->min_used_journal_sector = 1 + journal.cur_sector;
cur_sector = journal.cur_sector;
prepare_journal_sector_write(journal, cur_sector, sqe[s++], cb);
}
}
PRIV(op)->max_used_journal_sector = 1 + journal.cur_sector;
PRIV(op)->pending_ops = s;
PRIV(op)->sync_state = SYNC_JOURNAL_WRITE_SENT;
return 1;
}
if (PRIV(op)->sync_state == SYNC_JOURNAL_WRITE_DONE)
{
if (!disable_journal_fsync)
{
BS_SUBMIT_GET_SQE(sqe, data);
my_uring_prep_fsync(sqe, journal_fd_index, IORING_FSYNC_DATASYNC);
sqe->flags |= IOSQE_FIXED_FILE;
data->iov = { 0 };
data->callback = cb;
PRIV(op)->pending_ops = 1;
PRIV(op)->sync_state = SYNC_JOURNAL_SYNC_SENT;
return 1;
}
else
{
PRIV(op)->sync_state = SYNC_DONE;
}
}
if (PRIV(op)->sync_state == SYNC_DONE)
{
ack_sync(op);
}
return 1;
}
void blockstore_impl_t::handle_sync_event(ring_data_t *data, blockstore_op_t *op)
{
live = true;
if (data->res != data->iov.iov_len)
{
throw std::runtime_error(
"write operation failed ("+std::to_string(data->res)+" != "+std::to_string(data->iov.iov_len)+
"). in-memory state is corrupted. AAAAAAAaaaaaaaaa!!!111"
);
}
PRIV(op)->pending_ops--;
if (PRIV(op)->pending_ops == 0)
{
// Release used journal sectors
release_journal_sectors(op);
// Handle states
if (PRIV(op)->sync_state == SYNC_DATA_SYNC_SENT)
{
PRIV(op)->sync_state = SYNC_DATA_SYNC_DONE;
}
else if (PRIV(op)->sync_state == SYNC_JOURNAL_WRITE_SENT)
{
PRIV(op)->sync_state = SYNC_JOURNAL_WRITE_DONE;
}
else if (PRIV(op)->sync_state == SYNC_JOURNAL_SYNC_SENT)
{
PRIV(op)->sync_state = SYNC_DONE;
ack_sync(op);
}
else
{
throw std::runtime_error("BUG: unexpected sync op state");
}
}
}
int blockstore_impl_t::ack_sync(blockstore_op_t *op)
{
if (PRIV(op)->sync_state == SYNC_DONE && PRIV(op)->prev_sync_count == 0)
{
// Remove dependency of subsequent syncs
auto it = PRIV(op)->in_progress_ptr;
int done_syncs = 1;
++it;
// Acknowledge sync
ack_one_sync(op);
while (it != in_progress_syncs.end())
{
auto & next_sync = *it++;
PRIV(next_sync)->prev_sync_count -= done_syncs;
if (PRIV(next_sync)->prev_sync_count == 0 && PRIV(next_sync)->sync_state == SYNC_DONE)
{
done_syncs++;
// Acknowledge next_sync
ack_one_sync(next_sync);
}
}
return 1;
}
return 0;
}
void blockstore_impl_t::ack_one_sync(blockstore_op_t *op)
{
// Handle states
for (auto it = PRIV(op)->sync_big_writes.begin(); it != PRIV(op)->sync_big_writes.end(); it++)
{
#ifdef BLOCKSTORE_DEBUG
printf("Ack sync big %lu:%lu v%lu\n", it->oid.inode, it->oid.stripe, it->version);
#endif
auto & unstab = unstable_writes[it->oid];
unstab = unstab < it->version ? it->version : unstab;
dirty_db[*it].state = ST_D_META_SYNCED;
}
for (auto it = PRIV(op)->sync_small_writes.begin(); it != PRIV(op)->sync_small_writes.end(); it++)
{
#ifdef BLOCKSTORE_DEBUG
printf("Ack sync small %lu:%lu v%lu\n", it->oid.inode, it->oid.stripe, it->version);
#endif
auto & unstab = unstable_writes[it->oid];
unstab = unstab < it->version ? it->version : unstab;
dirty_db[*it].state = dirty_db[*it].state == ST_DEL_WRITTEN ? ST_DEL_SYNCED : ST_J_SYNCED;
}
in_progress_syncs.erase(PRIV(op)->in_progress_ptr);
op->retval = 0;
FINISH_OP(op);
}