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xemu/block/backup.c
John Snow 111049a4ec blockjob: refactor backup_start as backup_job_create 
Refactor backup_start as backup_job_create, which only creates the job,
but does not automatically start it. The old interface, 'backup_start',
is not kept in favor of limiting the number of nearly-identical interfaces
that would have to be edited to keep up with QAPI changes in the future.

Callers that wish to synchronously start the backup_block_job can
instead just call block_job_start immediately after calling
backup_job_create.

Transactions are updated to use the new interface, calling block_job_start
only during the .commit phase, which helps prevent race conditions where
jobs may finish before we even finish building the transaction. This may
happen, for instance, during empty block backup jobs.

Reported-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 1478587839-9834-6-git-send-email-jsnow@redhat.com
Signed-off-by: Jeff Cody <jcody@redhat.com>
2016-11-14 22:47:34 -05:00

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/*
* QEMU backup
*
* Copyright (C) 2013 Proxmox Server Solutions
*
* Authors:
* Dietmar Maurer (dietmar@proxmox.com)
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "trace.h"
#include "block/block.h"
#include "block/block_int.h"
#include "block/blockjob_int.h"
#include "block/block_backup.h"
#include "qapi/error.h"
#include "qapi/qmp/qerror.h"
#include "qemu/ratelimit.h"
#include "qemu/cutils.h"
#include "sysemu/block-backend.h"
#include "qemu/bitmap.h"
#define BACKUP_CLUSTER_SIZE_DEFAULT (1 << 16)
#define SLICE_TIME 100000000ULL /* ns */
typedef struct BackupBlockJob {
BlockJob common;
BlockBackend *target;
/* bitmap for sync=incremental */
BdrvDirtyBitmap *sync_bitmap;
MirrorSyncMode sync_mode;
RateLimit limit;
BlockdevOnError on_source_error;
BlockdevOnError on_target_error;
CoRwlock flush_rwlock;
uint64_t sectors_read;
unsigned long *done_bitmap;
int64_t cluster_size;
bool compress;
NotifierWithReturn before_write;
QLIST_HEAD(, CowRequest) inflight_reqs;
} BackupBlockJob;
/* Size of a cluster in sectors, instead of bytes. */
static inline int64_t cluster_size_sectors(BackupBlockJob *job)
{
return job->cluster_size / BDRV_SECTOR_SIZE;
}
/* See if in-flight requests overlap and wait for them to complete */
static void coroutine_fn wait_for_overlapping_requests(BackupBlockJob *job,
int64_t start,
int64_t end)
{
CowRequest *req;
bool retry;
do {
retry = false;
QLIST_FOREACH(req, &job->inflight_reqs, list) {
if (end > req->start && start < req->end) {
qemu_co_queue_wait(&req->wait_queue);
retry = true;
break;
}
}
} while (retry);
}
/* Keep track of an in-flight request */
static void cow_request_begin(CowRequest *req, BackupBlockJob *job,
int64_t start, int64_t end)
{
req->start = start;
req->end = end;
qemu_co_queue_init(&req->wait_queue);
QLIST_INSERT_HEAD(&job->inflight_reqs, req, list);
}
/* Forget about a completed request */
static void cow_request_end(CowRequest *req)
{
QLIST_REMOVE(req, list);
qemu_co_queue_restart_all(&req->wait_queue);
}
static int coroutine_fn backup_do_cow(BackupBlockJob *job,
int64_t sector_num, int nb_sectors,
bool *error_is_read,
bool is_write_notifier)
{
BlockBackend *blk = job->common.blk;
CowRequest cow_request;
struct iovec iov;
QEMUIOVector bounce_qiov;
void *bounce_buffer = NULL;
int ret = 0;
int64_t sectors_per_cluster = cluster_size_sectors(job);
int64_t start, end;
int n;
qemu_co_rwlock_rdlock(&job->flush_rwlock);
start = sector_num / sectors_per_cluster;
end = DIV_ROUND_UP(sector_num + nb_sectors, sectors_per_cluster);
trace_backup_do_cow_enter(job, start, sector_num, nb_sectors);
wait_for_overlapping_requests(job, start, end);
cow_request_begin(&cow_request, job, start, end);
for (; start < end; start++) {
if (test_bit(start, job->done_bitmap)) {
trace_backup_do_cow_skip(job, start);
continue; /* already copied */
}
trace_backup_do_cow_process(job, start);
n = MIN(sectors_per_cluster,
job->common.len / BDRV_SECTOR_SIZE -
start * sectors_per_cluster);
if (!bounce_buffer) {
bounce_buffer = blk_blockalign(blk, job->cluster_size);
}
iov.iov_base = bounce_buffer;
iov.iov_len = n * BDRV_SECTOR_SIZE;
qemu_iovec_init_external(&bounce_qiov, &iov, 1);
ret = blk_co_preadv(blk, start * job->cluster_size,
bounce_qiov.size, &bounce_qiov,
is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0);
if (ret < 0) {
trace_backup_do_cow_read_fail(job, start, ret);
if (error_is_read) {
*error_is_read = true;
}
goto out;
}
if (buffer_is_zero(iov.iov_base, iov.iov_len)) {
ret = blk_co_pwrite_zeroes(job->target, start * job->cluster_size,
bounce_qiov.size, BDRV_REQ_MAY_UNMAP);
} else {
ret = blk_co_pwritev(job->target, start * job->cluster_size,
bounce_qiov.size, &bounce_qiov,
job->compress ? BDRV_REQ_WRITE_COMPRESSED : 0);
}
if (ret < 0) {
trace_backup_do_cow_write_fail(job, start, ret);
if (error_is_read) {
*error_is_read = false;
}
goto out;
}
set_bit(start, job->done_bitmap);
/* Publish progress, guest I/O counts as progress too. Note that the
* offset field is an opaque progress value, it is not a disk offset.
*/
job->sectors_read += n;
job->common.offset += n * BDRV_SECTOR_SIZE;
}
out:
if (bounce_buffer) {
qemu_vfree(bounce_buffer);
}
cow_request_end(&cow_request);
trace_backup_do_cow_return(job, sector_num, nb_sectors, ret);
qemu_co_rwlock_unlock(&job->flush_rwlock);
return ret;
}
static int coroutine_fn backup_before_write_notify(
NotifierWithReturn *notifier,
void *opaque)
{
BackupBlockJob *job = container_of(notifier, BackupBlockJob, before_write);
BdrvTrackedRequest *req = opaque;
int64_t sector_num = req->offset >> BDRV_SECTOR_BITS;
int nb_sectors = req->bytes >> BDRV_SECTOR_BITS;
assert(req->bs == blk_bs(job->common.blk));
assert((req->offset & (BDRV_SECTOR_SIZE - 1)) == 0);
assert((req->bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
return backup_do_cow(job, sector_num, nb_sectors, NULL, true);
}
static void backup_set_speed(BlockJob *job, int64_t speed, Error **errp)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common);
if (speed < 0) {
error_setg(errp, QERR_INVALID_PARAMETER, "speed");
return;
}
ratelimit_set_speed(&s->limit, speed / BDRV_SECTOR_SIZE, SLICE_TIME);
}
static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
{
BdrvDirtyBitmap *bm;
BlockDriverState *bs = blk_bs(job->common.blk);
if (ret < 0 || block_job_is_cancelled(&job->common)) {
/* Merge the successor back into the parent, delete nothing. */
bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
assert(bm);
} else {
/* Everything is fine, delete this bitmap and install the backup. */
bm = bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL);
assert(bm);
}
}
static void backup_commit(BlockJob *job)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common);
if (s->sync_bitmap) {
backup_cleanup_sync_bitmap(s, 0);
}
}
static void backup_abort(BlockJob *job)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common);
if (s->sync_bitmap) {
backup_cleanup_sync_bitmap(s, -1);
}
}
static void backup_clean(BlockJob *job)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common);
assert(s->target);
blk_unref(s->target);
s->target = NULL;
}
static void backup_attached_aio_context(BlockJob *job, AioContext *aio_context)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common);
blk_set_aio_context(s->target, aio_context);
}
void backup_do_checkpoint(BlockJob *job, Error **errp)
{
BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
int64_t len;
assert(job->driver->job_type == BLOCK_JOB_TYPE_BACKUP);
if (backup_job->sync_mode != MIRROR_SYNC_MODE_NONE) {
error_setg(errp, "The backup job only supports block checkpoint in"
" sync=none mode");
return;
}
len = DIV_ROUND_UP(backup_job->common.len, backup_job->cluster_size);
bitmap_zero(backup_job->done_bitmap, len);
}
void backup_wait_for_overlapping_requests(BlockJob *job, int64_t sector_num,
int nb_sectors)
{
BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
int64_t sectors_per_cluster = cluster_size_sectors(backup_job);
int64_t start, end;
assert(job->driver->job_type == BLOCK_JOB_TYPE_BACKUP);
start = sector_num / sectors_per_cluster;
end = DIV_ROUND_UP(sector_num + nb_sectors, sectors_per_cluster);
wait_for_overlapping_requests(backup_job, start, end);
}
void backup_cow_request_begin(CowRequest *req, BlockJob *job,
int64_t sector_num,
int nb_sectors)
{
BackupBlockJob *backup_job = container_of(job, BackupBlockJob, common);
int64_t sectors_per_cluster = cluster_size_sectors(backup_job);
int64_t start, end;
assert(job->driver->job_type == BLOCK_JOB_TYPE_BACKUP);
start = sector_num / sectors_per_cluster;
end = DIV_ROUND_UP(sector_num + nb_sectors, sectors_per_cluster);
cow_request_begin(req, backup_job, start, end);
}
void backup_cow_request_end(CowRequest *req)
{
cow_request_end(req);
}
static void backup_drain(BlockJob *job)
{
BackupBlockJob *s = container_of(job, BackupBlockJob, common);
/* Need to keep a reference in case blk_drain triggers execution
* of backup_complete...
*/
if (s->target) {
BlockBackend *target = s->target;
blk_ref(target);
blk_drain(target);
blk_unref(target);
}
}
static BlockErrorAction backup_error_action(BackupBlockJob *job,
bool read, int error)
{
if (read) {
return block_job_error_action(&job->common, job->on_source_error,
true, error);
} else {
return block_job_error_action(&job->common, job->on_target_error,
false, error);
}
}
typedef struct {
int ret;
} BackupCompleteData;
static void backup_complete(BlockJob *job, void *opaque)
{
BackupCompleteData *data = opaque;
block_job_completed(job, data->ret);
g_free(data);
}
static bool coroutine_fn yield_and_check(BackupBlockJob *job)
{
if (block_job_is_cancelled(&job->common)) {
return true;
}
/* we need to yield so that bdrv_drain_all() returns.
* (without, VM does not reboot)
*/
if (job->common.speed) {
uint64_t delay_ns = ratelimit_calculate_delay(&job->limit,
job->sectors_read);
job->sectors_read = 0;
block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, delay_ns);
} else {
block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, 0);
}
if (block_job_is_cancelled(&job->common)) {
return true;
}
return false;
}
static int coroutine_fn backup_run_incremental(BackupBlockJob *job)
{
bool error_is_read;
int ret = 0;
int clusters_per_iter;
uint32_t granularity;
int64_t sector;
int64_t cluster;
int64_t end;
int64_t last_cluster = -1;
int64_t sectors_per_cluster = cluster_size_sectors(job);
BdrvDirtyBitmapIter *dbi;
granularity = bdrv_dirty_bitmap_granularity(job->sync_bitmap);
clusters_per_iter = MAX((granularity / job->cluster_size), 1);
dbi = bdrv_dirty_iter_new(job->sync_bitmap, 0);
/* Find the next dirty sector(s) */
while ((sector = bdrv_dirty_iter_next(dbi)) != -1) {
cluster = sector / sectors_per_cluster;
/* Fake progress updates for any clusters we skipped */
if (cluster != last_cluster + 1) {
job->common.offset += ((cluster - last_cluster - 1) *
job->cluster_size);
}
for (end = cluster + clusters_per_iter; cluster < end; cluster++) {
do {
if (yield_and_check(job)) {
goto out;
}
ret = backup_do_cow(job, cluster * sectors_per_cluster,
sectors_per_cluster, &error_is_read,
false);
if ((ret < 0) &&
backup_error_action(job, error_is_read, -ret) ==
BLOCK_ERROR_ACTION_REPORT) {
goto out;
}
} while (ret < 0);
}
/* If the bitmap granularity is smaller than the backup granularity,
* we need to advance the iterator pointer to the next cluster. */
if (granularity < job->cluster_size) {
bdrv_set_dirty_iter(dbi, cluster * sectors_per_cluster);
}
last_cluster = cluster - 1;
}
/* Play some final catchup with the progress meter */
end = DIV_ROUND_UP(job->common.len, job->cluster_size);
if (last_cluster + 1 < end) {
job->common.offset += ((end - last_cluster - 1) * job->cluster_size);
}
out:
bdrv_dirty_iter_free(dbi);
return ret;
}
static void coroutine_fn backup_run(void *opaque)
{
BackupBlockJob *job = opaque;
BackupCompleteData *data;
BlockDriverState *bs = blk_bs(job->common.blk);
int64_t start, end;
int64_t sectors_per_cluster = cluster_size_sectors(job);
int ret = 0;
QLIST_INIT(&job->inflight_reqs);
qemu_co_rwlock_init(&job->flush_rwlock);
start = 0;
end = DIV_ROUND_UP(job->common.len, job->cluster_size);
job->done_bitmap = bitmap_new(end);
job->before_write.notify = backup_before_write_notify;
bdrv_add_before_write_notifier(bs, &job->before_write);
if (job->sync_mode == MIRROR_SYNC_MODE_NONE) {
while (!block_job_is_cancelled(&job->common)) {
/* Yield until the job is cancelled. We just let our before_write
* notify callback service CoW requests. */
block_job_yield(&job->common);
}
} else if (job->sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
ret = backup_run_incremental(job);
} else {
/* Both FULL and TOP SYNC_MODE's require copying.. */
for (; start < end; start++) {
bool error_is_read;
if (yield_and_check(job)) {
break;
}
if (job->sync_mode == MIRROR_SYNC_MODE_TOP) {
int i, n;
int alloced = 0;
/* Check to see if these blocks are already in the
* backing file. */
for (i = 0; i < sectors_per_cluster;) {
/* bdrv_is_allocated() only returns true/false based
* on the first set of sectors it comes across that
* are are all in the same state.
* For that reason we must verify each sector in the
* backup cluster length. We end up copying more than
* needed but at some point that is always the case. */
alloced =
bdrv_is_allocated(bs,
start * sectors_per_cluster + i,
sectors_per_cluster - i, &n);
i += n;
if (alloced == 1 || n == 0) {
break;
}
}
/* If the above loop never found any sectors that are in
* the topmost image, skip this backup. */
if (alloced == 0) {
continue;
}
}
/* FULL sync mode we copy the whole drive. */
ret = backup_do_cow(job, start * sectors_per_cluster,
sectors_per_cluster, &error_is_read, false);
if (ret < 0) {
/* Depending on error action, fail now or retry cluster */
BlockErrorAction action =
backup_error_action(job, error_is_read, -ret);
if (action == BLOCK_ERROR_ACTION_REPORT) {
break;
} else {
start--;
continue;
}
}
}
}
notifier_with_return_remove(&job->before_write);
/* wait until pending backup_do_cow() calls have completed */
qemu_co_rwlock_wrlock(&job->flush_rwlock);
qemu_co_rwlock_unlock(&job->flush_rwlock);
g_free(job->done_bitmap);
data = g_malloc(sizeof(*data));
data->ret = ret;
block_job_defer_to_main_loop(&job->common, backup_complete, data);
}
static const BlockJobDriver backup_job_driver = {
.instance_size = sizeof(BackupBlockJob),
.job_type = BLOCK_JOB_TYPE_BACKUP,
.start = backup_run,
.set_speed = backup_set_speed,
.commit = backup_commit,
.abort = backup_abort,
.clean = backup_clean,
.attached_aio_context = backup_attached_aio_context,
.drain = backup_drain,
};
BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
BlockDriverState *target, int64_t speed,
MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
bool compress,
BlockdevOnError on_source_error,
BlockdevOnError on_target_error,
int creation_flags,
BlockCompletionFunc *cb, void *opaque,
BlockJobTxn *txn, Error **errp)
{
int64_t len;
BlockDriverInfo bdi;
BackupBlockJob *job = NULL;
int ret;
assert(bs);
assert(target);
if (bs == target) {
error_setg(errp, "Source and target cannot be the same");
return NULL;
}
if (!bdrv_is_inserted(bs)) {
error_setg(errp, "Device is not inserted: %s",
bdrv_get_device_name(bs));
return NULL;
}
if (!bdrv_is_inserted(target)) {
error_setg(errp, "Device is not inserted: %s",
bdrv_get_device_name(target));
return NULL;
}
if (compress && target->drv->bdrv_co_pwritev_compressed == NULL) {
error_setg(errp, "Compression is not supported for this drive %s",
bdrv_get_device_name(target));
return NULL;
}
if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_BACKUP_SOURCE, errp)) {
return NULL;
}
if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_BACKUP_TARGET, errp)) {
return NULL;
}
if (sync_mode == MIRROR_SYNC_MODE_INCREMENTAL) {
if (!sync_bitmap) {
error_setg(errp, "must provide a valid bitmap name for "
"\"incremental\" sync mode");
return NULL;
}
/* Create a new bitmap, and freeze/disable this one. */
if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
return NULL;
}
} else if (sync_bitmap) {
error_setg(errp,
"a sync_bitmap was provided to backup_run, "
"but received an incompatible sync_mode (%s)",
MirrorSyncMode_lookup[sync_mode]);
return NULL;
}
len = bdrv_getlength(bs);
if (len < 0) {
error_setg_errno(errp, -len, "unable to get length for '%s'",
bdrv_get_device_name(bs));
goto error;
}
job = block_job_create(job_id, &backup_job_driver, bs, speed,
creation_flags, cb, opaque, errp);
if (!job) {
goto error;
}
job->target = blk_new();
blk_insert_bs(job->target, target);
job->on_source_error = on_source_error;
job->on_target_error = on_target_error;
job->sync_mode = sync_mode;
job->sync_bitmap = sync_mode == MIRROR_SYNC_MODE_INCREMENTAL ?
sync_bitmap : NULL;
job->compress = compress;
/* If there is no backing file on the target, we cannot rely on COW if our
* backup cluster size is smaller than the target cluster size. Even for
* targets with a backing file, try to avoid COW if possible. */
ret = bdrv_get_info(target, &bdi);
if (ret < 0 && !target->backing) {
error_setg_errno(errp, -ret,
"Couldn't determine the cluster size of the target image, "
"which has no backing file");
error_append_hint(errp,
"Aborting, since this may create an unusable destination image\n");
goto error;
} else if (ret < 0 && target->backing) {
/* Not fatal; just trudge on ahead. */
job->cluster_size = BACKUP_CLUSTER_SIZE_DEFAULT;
} else {
job->cluster_size = MAX(BACKUP_CLUSTER_SIZE_DEFAULT, bdi.cluster_size);
}
block_job_add_bdrv(&job->common, target);
job->common.len = len;
block_job_txn_add_job(txn, &job->common);
return &job->common;
error:
if (sync_bitmap) {
bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
}
if (job) {
backup_clean(&job->common);
block_job_unref(&job->common);
}
return NULL;
}
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