xemu/block/copy-before-write.c
Vladimir Sementsov-Ogievskiy 8393078032 block: introduce bdrv_open_file_child() helper
Almost all drivers call bdrv_open_child() similarly. Let's create a
helper for this.

The only not updated drivers that call bdrv_open_child() to set
bs->file are raw-format and snapshot-access:
    raw-format sometimes want to have filtered child but
        don't set drv->is_filter to true.
    snapshot-access wants only DATA | PRIMARY

Possibly we should implement drv->is_filter_func() handler, to consider
raw-format as filter when it works as filter.. But it's another story.

Note also, that we decrease assignments to bs->file in code: it helps
us restrict modifying this field in further commit.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220726201134.924743-3-vsementsov@yandex-team.ru>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2022-10-27 20:14:11 +02:00

565 lines
16 KiB
C

/*
* 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 "qapi/qmp/qjson.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"
#include "block/reqlist.h"
#include "qapi/qapi-visit-block-core.h"
typedef struct BDRVCopyBeforeWriteState {
BlockCopyState *bcs;
BdrvChild *target;
OnCbwError on_cbw_error;
uint32_t cbw_timeout_ns;
/*
* @lock: protects access to @access_bitmap, @done_bitmap and
* @frozen_read_reqs
*/
CoMutex lock;
/*
* @access_bitmap: represents areas allowed for reading by fleecing user.
* Reading from non-dirty areas leads to -EACCES.
*/
BdrvDirtyBitmap *access_bitmap;
/*
* @done_bitmap: represents areas that was successfully copied to @target by
* copy-before-write operations.
*/
BdrvDirtyBitmap *done_bitmap;
/*
* @frozen_read_reqs: current read requests for fleecing user in bs->file
* node. These areas must not be rewritten by guest.
*/
BlockReqList frozen_read_reqs;
/*
* @snapshot_error is normally zero. But on first copy-before-write failure
* when @on_cbw_error == ON_CBW_ERROR_BREAK_SNAPSHOT, @snapshot_error takes
* value of this error (<0). After that all in-flight and further
* snapshot-API requests will fail with that error.
*/
int snapshot_error;
} BDRVCopyBeforeWriteState;
static coroutine_fn int cbw_co_preadv(
BlockDriverState *bs, int64_t offset, int64_t bytes,
QEMUIOVector *qiov, BdrvRequestFlags flags)
{
return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
}
static void block_copy_cb(void *opaque)
{
BlockDriverState *bs = opaque;
bdrv_dec_in_flight(bs);
}
/*
* Do copy-before-write operation.
*
* On failure guest request must be failed too.
*
* On success, we also wait for all in-flight fleecing read requests in source
* node, and it's guaranteed that after cbw_do_copy_before_write() successful
* return there are no such requests and they will never appear.
*/
static coroutine_fn int cbw_do_copy_before_write(BlockDriverState *bs,
uint64_t offset, uint64_t bytes, BdrvRequestFlags flags)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
int ret;
uint64_t off, end;
int64_t cluster_size = block_copy_cluster_size(s->bcs);
if (flags & BDRV_REQ_WRITE_UNCHANGED) {
return 0;
}
if (s->snapshot_error) {
return 0;
}
off = QEMU_ALIGN_DOWN(offset, cluster_size);
end = QEMU_ALIGN_UP(offset + bytes, cluster_size);
/*
* Increase in_flight, so that in case of timed-out block-copy, the
* remaining background block_copy() request (which can't be immediately
* cancelled by timeout) is presented in bs->in_flight. This way we are
* sure that on bs close() we'll previously wait for all timed-out but yet
* running block_copy calls.
*/
bdrv_inc_in_flight(bs);
ret = block_copy(s->bcs, off, end - off, true, s->cbw_timeout_ns,
block_copy_cb, bs);
if (ret < 0 && s->on_cbw_error == ON_CBW_ERROR_BREAK_GUEST_WRITE) {
return ret;
}
WITH_QEMU_LOCK_GUARD(&s->lock) {
if (ret < 0) {
assert(s->on_cbw_error == ON_CBW_ERROR_BREAK_SNAPSHOT);
if (!s->snapshot_error) {
s->snapshot_error = ret;
}
} else {
bdrv_set_dirty_bitmap(s->done_bitmap, off, end - off);
}
reqlist_wait_all(&s->frozen_read_reqs, off, end - off, &s->lock);
}
return 0;
}
static int coroutine_fn cbw_co_pdiscard(BlockDriverState *bs,
int64_t offset, int64_t bytes)
{
int ret = cbw_do_copy_before_write(bs, offset, bytes, 0);
if (ret < 0) {
return ret;
}
return bdrv_co_pdiscard(bs->file, offset, bytes);
}
static int coroutine_fn cbw_co_pwrite_zeroes(BlockDriverState *bs,
int64_t offset, int64_t 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->file, offset, bytes, flags);
}
static coroutine_fn int cbw_co_pwritev(BlockDriverState *bs,
int64_t offset,
int64_t bytes,
QEMUIOVector *qiov,
BdrvRequestFlags flags)
{
int ret = cbw_do_copy_before_write(bs, offset, bytes, flags);
if (ret < 0) {
return ret;
}
return bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
}
static int coroutine_fn cbw_co_flush(BlockDriverState *bs)
{
if (!bs->file) {
return 0;
}
return bdrv_co_flush(bs->file->bs);
}
/*
* If @offset not accessible - return NULL.
*
* Otherwise, set @pnum to some bytes that accessible from @file (@file is set
* to bs->file or to s->target). Return newly allocated BlockReq object that
* should be than passed to cbw_snapshot_read_unlock().
*
* It's guaranteed that guest writes will not interact in the region until
* cbw_snapshot_read_unlock() called.
*/
static coroutine_fn BlockReq *
cbw_snapshot_read_lock(BlockDriverState *bs, int64_t offset, int64_t bytes,
int64_t *pnum, BdrvChild **file)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
BlockReq *req = g_new(BlockReq, 1);
bool done;
QEMU_LOCK_GUARD(&s->lock);
if (s->snapshot_error) {
g_free(req);
return NULL;
}
if (bdrv_dirty_bitmap_next_zero(s->access_bitmap, offset, bytes) != -1) {
g_free(req);
return NULL;
}
done = bdrv_dirty_bitmap_status(s->done_bitmap, offset, bytes, pnum);
if (done) {
/*
* Special invalid BlockReq, that is handled in
* cbw_snapshot_read_unlock(). We don't need to lock something to read
* from s->target.
*/
*req = (BlockReq) {.offset = -1, .bytes = -1};
*file = s->target;
} else {
reqlist_init_req(&s->frozen_read_reqs, req, offset, bytes);
*file = bs->file;
}
return req;
}
static coroutine_fn void
cbw_snapshot_read_unlock(BlockDriverState *bs, BlockReq *req)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
if (req->offset == -1 && req->bytes == -1) {
g_free(req);
return;
}
QEMU_LOCK_GUARD(&s->lock);
reqlist_remove_req(req);
g_free(req);
}
static coroutine_fn int
cbw_co_preadv_snapshot(BlockDriverState *bs, int64_t offset, int64_t bytes,
QEMUIOVector *qiov, size_t qiov_offset)
{
BlockReq *req;
BdrvChild *file;
int ret;
/* TODO: upgrade to async loop using AioTask */
while (bytes) {
int64_t cur_bytes;
req = cbw_snapshot_read_lock(bs, offset, bytes, &cur_bytes, &file);
if (!req) {
return -EACCES;
}
ret = bdrv_co_preadv_part(file, offset, cur_bytes,
qiov, qiov_offset, 0);
cbw_snapshot_read_unlock(bs, req);
if (ret < 0) {
return ret;
}
bytes -= cur_bytes;
offset += cur_bytes;
qiov_offset += cur_bytes;
}
return 0;
}
static int coroutine_fn
cbw_co_snapshot_block_status(BlockDriverState *bs,
bool want_zero, int64_t offset, int64_t bytes,
int64_t *pnum, int64_t *map,
BlockDriverState **file)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
BlockReq *req;
int ret;
int64_t cur_bytes;
BdrvChild *child;
req = cbw_snapshot_read_lock(bs, offset, bytes, &cur_bytes, &child);
if (!req) {
return -EACCES;
}
ret = bdrv_block_status(child->bs, offset, cur_bytes, pnum, map, file);
if (child == s->target) {
/*
* We refer to s->target only for areas that we've written to it.
* And we can not report unallocated blocks in s->target: this will
* break generic block-status-above logic, that will go to
* copy-before-write filtered child in this case.
*/
assert(ret & BDRV_BLOCK_ALLOCATED);
}
cbw_snapshot_read_unlock(bs, req);
return ret;
}
static int coroutine_fn cbw_co_pdiscard_snapshot(BlockDriverState *bs,
int64_t offset, int64_t bytes)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
WITH_QEMU_LOCK_GUARD(&s->lock) {
bdrv_reset_dirty_bitmap(s->access_bitmap, offset, bytes);
}
block_copy_reset(s->bcs, offset, bytes);
return bdrv_co_pdiscard(s->target, offset, bytes);
}
static void cbw_refresh_filename(BlockDriverState *bs)
{
pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
bs->file->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 (!QLIST_EMPTY(&bs->parents)) {
if (perm & BLK_PERM_WRITE) {
*nperm = *nperm | BLK_PERM_CONSISTENT_READ;
}
*nshared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
}
}
}
static BlockdevOptions *cbw_parse_options(QDict *options, Error **errp)
{
BlockdevOptions *opts = NULL;
Visitor *v = NULL;
qdict_put_str(options, "driver", "copy-before-write");
v = qobject_input_visitor_new_flat_confused(options, errp);
if (!v) {
goto out;
}
visit_type_BlockdevOptions(v, NULL, &opts, errp);
if (!opts) {
goto out;
}
/*
* Delete options which we are going to parse through BlockdevOptions
* object for original options.
*/
qdict_extract_subqdict(options, NULL, "bitmap");
qdict_del(options, "on-cbw-error");
qdict_del(options, "cbw-timeout");
out:
visit_free(v);
qdict_del(options, "driver");
return opts;
}
static int cbw_open(BlockDriverState *bs, QDict *options, int flags,
Error **errp)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
BdrvDirtyBitmap *bitmap = NULL;
int64_t cluster_size;
g_autoptr(BlockdevOptions) full_opts = NULL;
BlockdevOptionsCbw *opts;
int ret;
full_opts = cbw_parse_options(options, errp);
if (!full_opts) {
return -EINVAL;
}
assert(full_opts->driver == BLOCKDEV_DRIVER_COPY_BEFORE_WRITE);
opts = &full_opts->u.copy_before_write;
ret = bdrv_open_file_child(NULL, options, "file", bs, errp);
if (ret < 0) {
return ret;
}
s->target = bdrv_open_child(NULL, options, "target", bs, &child_of_bds,
BDRV_CHILD_DATA, false, errp);
if (!s->target) {
return -EINVAL;
}
if (opts->has_bitmap) {
bitmap = block_dirty_bitmap_lookup(opts->bitmap->node,
opts->bitmap->name, NULL, errp);
if (!bitmap) {
return -EINVAL;
}
}
s->on_cbw_error = opts->has_on_cbw_error ? opts->on_cbw_error :
ON_CBW_ERROR_BREAK_GUEST_WRITE;
s->cbw_timeout_ns = opts->has_cbw_timeout ?
opts->cbw_timeout * NANOSECONDS_PER_SECOND : 0;
bs->total_sectors = bs->file->bs->total_sectors;
bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
(BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
bs->file->bs->supported_zero_flags);
s->bcs = block_copy_state_new(bs->file, s->target, bitmap, errp);
if (!s->bcs) {
error_prepend(errp, "Cannot create block-copy-state: ");
return -EINVAL;
}
cluster_size = block_copy_cluster_size(s->bcs);
s->done_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
if (!s->done_bitmap) {
return -EINVAL;
}
bdrv_disable_dirty_bitmap(s->done_bitmap);
/* s->access_bitmap starts equal to bcs bitmap */
s->access_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
if (!s->access_bitmap) {
return -EINVAL;
}
bdrv_disable_dirty_bitmap(s->access_bitmap);
bdrv_dirty_bitmap_merge_internal(s->access_bitmap,
block_copy_dirty_bitmap(s->bcs), NULL,
true);
qemu_co_mutex_init(&s->lock);
QLIST_INIT(&s->frozen_read_reqs);
return 0;
}
static void cbw_close(BlockDriverState *bs)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
bdrv_release_dirty_bitmap(s->access_bitmap);
bdrv_release_dirty_bitmap(s->done_bitmap);
block_copy_state_free(s->bcs);
s->bcs = NULL;
}
BlockDriver bdrv_cbw_filter = {
.format_name = "copy-before-write",
.instance_size = sizeof(BDRVCopyBeforeWriteState),
.bdrv_open = cbw_open,
.bdrv_close = cbw_close,
.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_co_preadv_snapshot = cbw_co_preadv_snapshot,
.bdrv_co_pdiscard_snapshot = cbw_co_pdiscard_snapshot,
.bdrv_co_snapshot_block_status = cbw_co_snapshot_block_status,
.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,
BlockCopyState **bcs,
Error **errp)
{
ERRP_GUARD();
BDRVCopyBeforeWriteState *state;
BlockDriverState *top;
QDict *opts;
assert(source->total_sectors == target->total_sectors);
GLOBAL_STATE_CODE();
opts = qdict_new();
qdict_put_str(opts, "driver", "copy-before-write");
if (filter_node_name) {
qdict_put_str(opts, "node-name", filter_node_name);
}
qdict_put_str(opts, "file", bdrv_get_node_name(source));
qdict_put_str(opts, "target", bdrv_get_node_name(target));
top = bdrv_insert_node(source, opts, BDRV_O_RDWR, errp);
if (!top) {
return NULL;
}
state = top->opaque;
*bcs = state->bcs;
return top;
}
void bdrv_cbw_drop(BlockDriverState *bs)
{
GLOBAL_STATE_CODE();
bdrv_drop_filter(bs, &error_abort);
bdrv_unref(bs);
}
static void cbw_init(void)
{
bdrv_register(&bdrv_cbw_filter);
}
block_init(cbw_init);