qemu/block/copy-before-write.c
Kevin Wolf 9102f2ebdb copy-before-write: Fix open with child in iothread
The AioContext lock must not be held for bdrv_open_child(), but it is
necessary for the following operations, in particular those using nested
event loops in coroutine wrappers.

Temporarily dropping the main AioContext lock is not necessary because
we know we run in the main thread.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230525124713.401149-9-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2023-05-30 17:29:35 +02:00

575 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/dirty-bitmap.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 int coroutine_fn GRAPH_RDLOCK
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 GRAPH_RDLOCK
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 GRAPH_RDLOCK
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 GRAPH_RDLOCK
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 GRAPH_RDLOCK 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 int coroutine_fn GRAPH_RDLOCK
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 GRAPH_RDLOCK
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 GRAPH_RDLOCK
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;
AioContext *ctx;
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;
}
ctx = bdrv_get_aio_context(bs);
aio_context_acquire(ctx);
if (opts->bitmap) {
bitmap = block_dirty_bitmap_lookup(opts->bitmap->node,
opts->bitmap->name, NULL, errp);
if (!bitmap) {
ret = -EINVAL;
goto out;
}
}
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: ");
ret = -EINVAL;
goto out;
}
cluster_size = block_copy_cluster_size(s->bcs);
s->done_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
if (!s->done_bitmap) {
ret = -EINVAL;
goto out;
}
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) {
ret = -EINVAL;
goto out;
}
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);
ret = 0;
out:
aio_context_release(ctx);
return ret;
}
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)
{
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);