Simplified distributed block storage with strong consistency, like in Ceph
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#include "blockstore.h"
blockstore_journal_check_t::blockstore_journal_check_t(blockstore *bs)
{
this->bs = bs;
sectors_required = 0;
next_pos = bs->journal.next_free;
next_sector = bs->journal.cur_sector;
next_in_pos = bs->journal.in_sector_pos;
}
// Check if we can write <required> entries of <size> bytes and <data_after> data bytes after them to the journal
int blockstore_journal_check_t::check_available(blockstore_operation *op, int required, int size, int data_after)
{
while (1)
{
int fits = (512 - next_in_pos) / size;
if (fits > 0)
{
required -= fits;
next_in_pos += fits * size;
sectors_required++;
}
if (required <= 0)
break;
next_pos = (next_pos+512) < bs->journal.len ? next_pos+512 : 512;
next_sector = ((next_sector + 1) % bs->journal.sector_count);
next_in_pos = 0;
if (bs->journal.sector_info[next_sector].usage_count > 0)
{
// No memory buffer available. Wait for it.
op->wait_for = WAIT_JOURNAL_BUFFER;
return 0;
}
}
if (data_after > 0)
{
next_pos = (bs->journal.len - next_pos < data_after ? 512 : next_pos) + data_after;
}
if (next_pos >= bs->journal.used_start)
{
// No space in the journal. Wait for it.
op->wait_for = WAIT_JOURNAL;
op->wait_detail = next_pos;
return 0;
}
return 1;
}
void prepare_journal_sector_write(blockstore_operation *op, journal_t & journal, io_uring_sqe *sqe)
{
journal.sector_info[journal.cur_sector].usage_count++;
struct ring_data_t *data = ((ring_data_t*)sqe->user_data);
data->iov = (struct iovec){ journal.sector_buf + 512*journal.cur_sector, 512 };
data->op = op;
io_uring_prep_writev(
sqe, journal.fd, &data->iov, 1, journal.offset + journal.sector_info[journal.cur_sector].offset
);
}