/*
* copy-before-write filter driver
*
* The driver performs Copy-Before-Write (CBW) operation: it is injected above
* some node, and before each write it copies _old_ data to the target node.
*
* Copyright (c) 2018-2021 Virtuozzo International GmbH.
*
* Author:
* Sementsov-Ogievskiy Vladimir <vsementsov@virtuozzo.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "qemu/osdep.h"
#include "sysemu/block-backend.h"
#include "qemu/cutils.h"
#include "qapi/error.h"
#include "block/block_int.h"
#include "block/qdict.h"
#include "block/block-copy.h"
#include "block/copy-before-write.h"
typedef struct BDRVCopyBeforeWriteState {
BlockCopyState *bcs;
BdrvChild *target;
int64_t cluster_size;
} BDRVCopyBeforeWriteState;
static coroutine_fn int cbw_co_preadv(
BlockDriverState *bs, uint64_t offset, uint64_t bytes,
QEMUIOVector *qiov, int flags)
{
return bdrv_co_preadv(bs->backing, offset, bytes, qiov, flags);
}
static coroutine_fn int cbw_do_copy_before_write(BlockDriverState *bs,
uint64_t offset, uint64_t bytes, BdrvRequestFlags flags)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
uint64_t off, end;
if (flags & BDRV_REQ_WRITE_UNCHANGED) {
return 0;
}
off = QEMU_ALIGN_DOWN(offset, s->cluster_size);
end = QEMU_ALIGN_UP(offset + bytes, s->cluster_size);
return block_copy(s->bcs, off, end - off, true);
}
static int coroutine_fn cbw_co_pdiscard(BlockDriverState *bs,
int64_t offset, int bytes)
{
int ret = cbw_do_copy_before_write(bs, offset, bytes, 0);
if (ret < 0) {
return ret;
}
return bdrv_co_pdiscard(bs->backing, offset, bytes);
}
static int coroutine_fn cbw_co_pwrite_zeroes(BlockDriverState *bs,
int64_t offset, int bytes, BdrvRequestFlags flags)
{
int ret = cbw_do_copy_before_write(bs, offset, bytes, flags);
if (ret < 0) {
return ret;
}
return bdrv_co_pwrite_zeroes(bs->backing, offset, bytes, flags);
}
static coroutine_fn int cbw_co_pwritev(BlockDriverState *bs,
uint64_t offset,
uint64_t bytes,
QEMUIOVector *qiov, int flags)
{
int ret = cbw_do_copy_before_write(bs, offset, bytes, flags);
if (ret < 0) {
return ret;
}
return bdrv_co_pwritev(bs->backing, offset, bytes, qiov, flags);
}
static int coroutine_fn cbw_co_flush(BlockDriverState *bs)
{
if (!bs->backing) {
return 0;
}
return bdrv_co_flush(bs->backing->bs);
}
static void cbw_refresh_filename(BlockDriverState *bs)
{
if (bs->backing == NULL) {
/*
* we can be here after failed bdrv_attach_child in
* bdrv_set_backing_hd
*/
return;
}
pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
bs->backing->bs->filename);
}
static void cbw_child_perm(BlockDriverState *bs, BdrvChild *c,
BdrvChildRole role,
BlockReopenQueue *reopen_queue,
uint64_t perm, uint64_t shared,
uint64_t *nperm, uint64_t *nshared)
{
if (!(role & BDRV_CHILD_FILTERED)) {
/*
* Target child
*
* Share write to target (child_file), to not interfere
* with guest writes to its disk which may be in target backing chain.
* Can't resize during a backup block job because we check the size
* only upfront.
*/
*nshared = BLK_PERM_ALL & ~BLK_PERM_RESIZE;
*nperm = BLK_PERM_WRITE;
} else {
/* Source child */
bdrv_default_perms(bs, c, role, reopen_queue,
perm, shared, nperm, nshared);
if (perm & BLK_PERM_WRITE) {
*nperm = *nperm | BLK_PERM_CONSISTENT_READ;
}
*nshared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
}
}
BlockDriver bdrv_cbw_filter = {
.format_name = "copy-before-write",
.instance_size = sizeof(BDRVCopyBeforeWriteState),
.bdrv_co_preadv = cbw_co_preadv,
.bdrv_co_pwritev = cbw_co_pwritev,
.bdrv_co_pwrite_zeroes = cbw_co_pwrite_zeroes,
.bdrv_co_pdiscard = cbw_co_pdiscard,
.bdrv_co_flush = cbw_co_flush,
.bdrv_refresh_filename = cbw_refresh_filename,
.bdrv_child_perm = cbw_child_perm,
.is_filter = true,
};
BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
BlockDriverState *target,
const char *filter_node_name,
uint64_t cluster_size,
bool compress,
BlockCopyState **bcs,
Error **errp)
{
ERRP_GUARD();
int ret;
BDRVCopyBeforeWriteState *state;
BlockDriverState *top;
bool appended = false;
assert(source->total_sectors == target->total_sectors);
top = bdrv_new_open_driver(&bdrv_cbw_filter, filter_node_name,
BDRV_O_RDWR, errp);
if (!top) {
return NULL;
}
state = top->opaque;
top->total_sectors = source->total_sectors;
top->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
(BDRV_REQ_FUA & source->supported_write_flags);
top->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
source->supported_zero_flags);
bdrv_ref(target);
state->target = bdrv_attach_child(top, target, "target", &child_of_bds,
BDRV_CHILD_DATA, errp);
if (!state->target) {
bdrv_unref(target);
bdrv_unref(top);
return NULL;
}
bdrv_drained_begin(source);
ret = bdrv_append(top, source, errp);
if (ret < 0) {
error_prepend(errp, "Cannot append copy-before-write filter: ");
goto fail;
}
appended = true;
state->cluster_size = cluster_size;
state->bcs = block_copy_state_new(top->backing, state->target,
cluster_size, false, compress, errp);
if (!state->bcs) {
error_prepend(errp, "Cannot create block-copy-state: ");
goto fail;
}
*bcs = state->bcs;
bdrv_drained_end(source);
return top;
fail:
if (appended) {
bdrv_cbw_drop(top);
} else {
bdrv_unref(top);
}
bdrv_drained_end(source);
return NULL;
}
void bdrv_cbw_drop(BlockDriverState *bs)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
bdrv_drop_filter(bs, &error_abort);
block_copy_state_free(s->bcs);
bdrv_unref(bs);
}
