Simplified distributed block storage with strong consistency, like in Ceph
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// Copyright (c) Vitaliy Filippov, 2019+
// License: VNPL-1.0 (see README.md for details)
#include <string.h>
#include <assert.h>
#include "xor.h"
#include "osd_rmw.h"
#include "malloc_or_die.h"
static inline void extend_read(uint32_t start, uint32_t end, osd_rmw_stripe_t & stripe)
{
if (stripe.read_end == 0)
{
stripe.read_start = start;
stripe.read_end = end;
}
else
{
if (stripe.read_end < end)
stripe.read_end = end;
if (stripe.read_start > start)
stripe.read_start = start;
}
}
static inline void cover_read(uint32_t start, uint32_t end, osd_rmw_stripe_t & stripe)
{
// Subtract <to> write request from <from> request
if (start >= stripe.req_start &&
end <= stripe.req_end)
{
return;
}
if (start <= stripe.req_start &&
end >= stripe.req_start &&
end <= stripe.req_end)
{
end = stripe.req_start;
}
else if (start >= stripe.req_start &&
start <= stripe.req_end &&
end >= stripe.req_end)
{
start = stripe.req_end;
}
if (stripe.read_end == 0)
{
stripe.read_start = start;
stripe.read_end = end;
}
else
{
if (stripe.read_end < end)
stripe.read_end = end;
if (stripe.read_start > start)
stripe.read_start = start;
}
}
void split_stripes(uint64_t pg_minsize, uint32_t bs_block_size, uint32_t start, uint32_t end, osd_rmw_stripe_t *stripes)
{
if (end == 0)
{
// Zero length request - offset doesn't matter
return;
}
end = start+end;
for (int role = 0; role < pg_minsize; role++)
{
if (start < (1+role)*bs_block_size && end > role*bs_block_size)
{
stripes[role].req_start = start < role*bs_block_size ? 0 : start-role*bs_block_size;
stripes[role].req_end = end > (role+1)*bs_block_size ? bs_block_size : end-role*bs_block_size;
}
}
}
void reconstruct_stripe_xor(osd_rmw_stripe_t *stripes, int pg_size, int role)
{
int prev = -2;
for (int other = 0; other < pg_size; other++)
{
if (other != role)
{
if (prev == -2)
{
prev = other;
}
else if (prev >= 0)
{
assert(stripes[role].read_start >= stripes[prev].read_start &&
stripes[role].read_start >= stripes[other].read_start);
memxor(
stripes[prev].read_buf + (stripes[role].read_start - stripes[prev].read_start),
stripes[other].read_buf + (stripes[role].read_start - stripes[other].read_start),
stripes[role].read_buf, stripes[role].read_end - stripes[role].read_start
);
prev = -1;
}
else
{
assert(stripes[role].read_start >= stripes[other].read_start);
memxor(
stripes[role].read_buf,
stripes[other].read_buf + (stripes[role].read_start - stripes[other].read_start),
stripes[role].read_buf, stripes[role].read_end - stripes[role].read_start
);
}
}
}
}
int extend_missing_stripes(osd_rmw_stripe_t *stripes, osd_num_t *osd_set, int minsize, int size)
{
for (int role = 0; role < minsize; role++)
{
if (stripes[role].read_end != 0 && osd_set[role] == 0)
{
stripes[role].missing = true;
// Stripe is missing. Extend read to other stripes.
// We need at least pg_minsize stripes to recover the lost part.
// FIXME: LRC EC and similar don't require to read all other stripes.
int exist = 0;
for (int j = 0; j < size; j++)
{
if (osd_set[j] != 0)
{
extend_read(stripes[role].read_start, stripes[role].read_end, stripes[j]);
exist++;
if (exist >= minsize)
{
break;
}
}
}
if (exist < minsize)
{
// Less than minsize stripes are available for this object
return -1;
}
}
}
return 0;
}
void* alloc_read_buffer(osd_rmw_stripe_t *stripes, int read_pg_size, uint64_t add_size)
{
// Calculate buffer size
uint64_t buf_size = add_size;
for (int role = 0; role < read_pg_size; role++)
{
if (stripes[role].read_end != 0)
{
buf_size += stripes[role].read_end - stripes[role].read_start;
}
}
// Allocate buffer
void *buf = memalign_or_die(MEM_ALIGNMENT, buf_size);
uint64_t buf_pos = add_size;
for (int role = 0; role < read_pg_size; role++)
{
if (stripes[role].read_end != 0)
{
stripes[role].read_buf = buf + buf_pos;
buf_pos += stripes[role].read_end - stripes[role].read_start;
}
}
return buf;
}
void* calc_rmw(void *request_buf, osd_rmw_stripe_t *stripes, uint64_t *read_osd_set,
uint64_t pg_size, uint64_t pg_minsize, uint64_t pg_cursize, uint64_t *write_osd_set, uint64_t chunk_size)
{
// Generic parity modification (read-modify-write) algorithm
// Read -> Reconstruct missing chunks -> Calc parity chunks -> Write
// Now we always read continuous ranges. This means that an update of the beginning
// of one data stripe and the end of another will lead to a read of full paired stripes.
// FIXME: (Maybe) read small individual ranges in that case instead.
uint32_t start = 0, end = 0;
for (int role = 0; role < pg_minsize; role++)
{
if (stripes[role].req_end != 0)
{
start = !end || stripes[role].req_start < start ? stripes[role].req_start : start;
end = std::max(stripes[role].req_end, end);
stripes[role].write_start = stripes[role].req_start;
stripes[role].write_end = stripes[role].req_end;
}
}
int write_parity = 0;
for (int role = pg_minsize; role < pg_size; role++)
{
if (write_osd_set[role] != 0)
{
write_parity = 1;
stripes[role].write_start = start;
stripes[role].write_end = end;
}
}
if (write_parity)
{
for (int role = 0; role < pg_minsize; role++)
{
cover_read(start, end, stripes[role]);
}
}
if (write_osd_set != read_osd_set)
{
pg_cursize = 0;
// Object is degraded/misplaced and will be moved to <write_osd_set>
for (int role = 0; role < pg_size; role++)
{
if (write_osd_set[role] != read_osd_set[role] && write_osd_set[role] != 0)
{
// We need to get data for any moved / recovered chunk
// And we need a continuous write buffer so we'll only optimize
// for the case when the whole chunk is ovewritten in the request
if (stripes[role].req_start != 0 ||
stripes[role].req_end != chunk_size)
{
stripes[role].read_start = 0;
stripes[role].read_end = chunk_size;
// Warning: We don't modify write_start/write_end here, we do it in calc_rmw_parity()
}
}
if (read_osd_set[role] != 0)
{
pg_cursize++;
}
}
}
if (pg_cursize < pg_size)
{
// Some stripe(s) are missing, so we need to read parity
for (int role = 0; role < pg_size; role++)
{
if (read_osd_set[role] == 0)
{
stripes[role].missing = true;
if (stripes[role].read_end != 0)
{
int found = 0;
for (int r2 = 0; r2 < pg_size && found < pg_minsize; r2++)
{
// Read the non-covered range of <role> from at least <minsize> other stripes to reconstruct it
if (read_osd_set[r2] != 0)
{
extend_read(stripes[role].read_start, stripes[role].read_end, stripes[r2]);
found++;
}
}
if (found < pg_minsize)
{
// FIXME Object is incomplete - refuse partial overwrite
assert(0);
}
}
}
}
}
// Allocate read buffers
void *rmw_buf = alloc_read_buffer(stripes, pg_size, (write_parity ? pg_size-pg_minsize : 0) * (end - start));
// Position write buffers
uint64_t buf_pos = 0, in_pos = 0;
for (int role = 0; role < pg_size; role++)
{
if (stripes[role].req_end != 0)
{
stripes[role].write_buf = request_buf + in_pos;
in_pos += stripes[role].req_end - stripes[role].req_start;
}
else if (role >= pg_minsize && write_osd_set[role] != 0 && end != 0)
{
stripes[role].write_buf = rmw_buf + buf_pos;
buf_pos += end - start;
}
}
return rmw_buf;
}
static void get_old_new_buffers(osd_rmw_stripe_t & stripe, uint32_t wr_start, uint32_t wr_end, buf_len_t *bufs, int & nbufs)
{
uint32_t ns = 0, ne = 0, os = 0, oe = 0;
if (stripe.req_end > wr_start &&
stripe.req_start < wr_end)
{
ns = std::max(stripe.req_start, wr_start);
ne = std::min(stripe.req_end, wr_end);
}
if (stripe.read_end > wr_start &&
stripe.read_start < wr_end)
{
os = std::max(stripe.read_start, wr_start);
oe = std::min(stripe.read_end, wr_end);
}
if (ne && (!oe || ns <= os))
{
// NEW or NEW->OLD
bufs[nbufs++] = { .buf = stripe.write_buf + ns - stripe.req_start, .len = ne-ns };
if (os < ne)
os = ne;
if (oe > os)
{
// NEW->OLD
bufs[nbufs++] = { .buf = stripe.read_buf + os - stripe.read_start, .len = oe-os };
}
}
else if (oe)
{
// OLD or OLD->NEW or OLD->NEW->OLD
if (ne)
{
// OLD->NEW or OLD->NEW->OLD
bufs[nbufs++] = { .buf = stripe.read_buf + os - stripe.read_start, .len = ns-os };
bufs[nbufs++] = { .buf = stripe.write_buf + ns - stripe.req_start, .len = ne-ns };
if (oe > ne)
{
// OLD->NEW->OLD
bufs[nbufs++] = { .buf = stripe.read_buf + ne - stripe.read_start, .len = oe-ne };
}
}
else
{
// OLD
bufs[nbufs++] = { .buf = stripe.read_buf + os - stripe.read_start, .len = oe-os };
}
}
}
static void xor_multiple_buffers(buf_len_t *xor1, int n1, buf_len_t *xor2, int n2, void *dest, uint32_t len)
{
assert(n1 > 0 && n2 > 0);
int i1 = 0, i2 = 0;
uint32_t start1 = 0, start2 = 0, end1 = xor1[0].len, end2 = xor2[0].len;
uint32_t pos = 0;
while (pos < len)
{
// We know for sure that ranges overlap
uint32_t end = std::min(end1, end2);
memxor(xor1[i1].buf + pos-start1, xor2[i2].buf + pos-start2, dest+pos, end-pos);
pos = end;
if (pos >= end1)
{
i1++;
if (i1 >= n1)
{
assert(pos >= end2);
return;
}
start1 = end1;
end1 += xor1[i1].len;
}
if (pos >= end2)
{
i2++;
start2 = end2;
end2 += xor2[i2].len;
}
}
}
void calc_rmw_parity_xor(osd_rmw_stripe_t *stripes, int pg_size, uint64_t *read_osd_set, uint64_t *write_osd_set, uint32_t chunk_size)
{
int pg_minsize = pg_size-1;
for (int role = 0; role < pg_size; role++)
{
if (stripes[role].read_end != 0 && stripes[role].missing)
{
// Reconstruct missing stripe (XOR k+1)
reconstruct_stripe_xor(stripes, pg_size, role);
break;
}
}
uint32_t start = 0, end = 0;
if (write_osd_set[pg_minsize] != 0 || write_osd_set != read_osd_set)
{
// Required for the next two if()s
for (int role = 0; role < pg_minsize; role++)
{
if (stripes[role].req_end != 0)
{
start = !end || stripes[role].req_start < start ? stripes[role].req_start : start;
end = std::max(stripes[role].req_end, end);
}
}
}
if (write_osd_set != read_osd_set)
{
for (int role = 0; role < pg_minsize; role++)
{
if (write_osd_set[role] != read_osd_set[role] && write_osd_set[role] != 0 &&
(stripes[role].req_start != 0 || stripes[role].req_end != chunk_size))
{
// Copy modified chunk into the read buffer to write it back
memcpy(
stripes[role].read_buf + stripes[role].req_start,
stripes[role].write_buf,
stripes[role].req_end - stripes[role].req_start
);
stripes[role].write_buf = stripes[role].read_buf;
stripes[role].write_start = 0;
stripes[role].write_end = chunk_size;
}
}
}
if (write_osd_set[pg_minsize] != 0 && end != 0)
{
// Calculate new parity (XOR k+1)
int parity = pg_minsize, prev = -2;
for (int other = 0; other < pg_minsize; other++)
{
if (prev == -2)
{
prev = other;
}
else
{
int n1 = 0, n2 = 0;
buf_len_t xor1[3], xor2[3];
if (prev == -1)
{
xor1[n1++] = { .buf = stripes[parity].write_buf, .len = end-start };
}
else
{
get_old_new_buffers(stripes[prev], start, end, xor1, n1);
prev = -1;
}
get_old_new_buffers(stripes[other], start, end, xor2, n2);
xor_multiple_buffers(xor1, n1, xor2, n2, stripes[parity].write_buf, end-start);
}
}
}
if (write_osd_set != read_osd_set)
{
for (int role = pg_minsize; role < pg_size; role++)
{
if (write_osd_set[role] != read_osd_set[role] && (start != 0 || end != chunk_size))
{
// Copy new parity into the read buffer to write it back
memcpy(
stripes[role].read_buf + start,
stripes[role].write_buf,
end - start
);
stripes[role].write_buf = stripes[role].read_buf;
stripes[role].write_start = 0;
stripes[role].write_end = chunk_size;
}
}
}
}