Simplified distributed block storage with strong consistency, like in Ceph
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
 
 
 
 
 
 

188 lines
6.5 KiB

#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 = clean_db.find(op->oid);
if (clean_it != clean_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,
});
// Remember write as unsynced here, so external consumers could get
// the list of dirty objects to sync just before issuing a SYNC request
if (op->len == block_size || op->version == 1)
{
// Remember big write as unsynced
unsynced_big_writes.push_back((obj_ver_id){
.oid = op->oid,
.version = op->version,
});
}
else
{
// Remember small write as unsynced
unsynced_small_writes.push_back((obj_ver_id){
.oid = op->oid,
.version = op->version,
});
}
}
// 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 || op->version == 1)
{
// Big (redirect) write
uint64_t loc = allocator_find_free(data_alloc);
if (loc == UINT64_MAX)
{
// 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);
int vcnt = 0;
if (op->version == 1 && op->len != block_size)
{
// zero fill newly allocated object
// This thing turns new small writes into big writes
// So FIXME: consider writing an empty big_write as version 1 instead of zero-filling here
if (op->offset > 0)
op->iov_zerofill[vcnt++] = (struct iovec){ zero_object, op->offset };
op->iov_zerofill[vcnt++] = (struct iovec){ op->buf, op->len };
if (op->offset+op->len < block_size)
op->iov_zerofill[vcnt++] = (struct iovec){ zero_object, block_size - (op->offset + op->len) };
}
else
{
vcnt = 1;
op->iov_zerofill[0] = (struct iovec){ op->buf, op->len };
}
data->op = op;
io_uring_prep_writev(
sqe, data_fd, op->iov_zerofill, vcnt, 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
//two_sqes = (512 - journal.in_sector_pos < sizeof(struct journal_entry_small_write)
// ? (journal.len - next_pos < op->len)
// : (journal.sector_info[journal.cur_sector].offset + 512 != journal.next_free ||
// journal.len - next_pos < op->len);
blockstore_journal_check_t space_check(this);
if (!space_check.check_available(op, 1, sizeof(journal_entry_small_write), op->len))
{
return 0;
}
// There is sufficient space. Get SQE(s)
BS_SUBMIT_GET_ONLY_SQE(sqe1);
BS_SUBMIT_GET_SQE(sqe2, data2);
// Got SQEs. Prepare journal sector write
journal_entry_small_write *je = (journal_entry_small_write*)
prefill_single_journal_entry(journal, JE_SMALL_WRITE, sizeof(struct journal_entry_small_write));
je->oid = op->oid;
je->version = op->version;
je->offset = op->offset;
je->len = op->len;
je->crc32 = je_crc32((journal_entry*)je);
journal.crc32_last = je->crc32;
prepare_journal_sector_write(op, journal, sqe1);
op->min_used_journal_sector = op->max_used_journal_sector = 1 + journal.cur_sector;
// Prepare journal data write
journal.next_free = (journal.next_free + op->len) < journal.len ? journal.next_free : 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;
journal.next_free += op->len;
op->pending_ops = 2;
}
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);
}
}