qemu/block/stream.c

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/*
* Image streaming
*
* Copyright IBM, Corp. 2011
*
* Authors:
* Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
*
* This work is licensed under the terms of the GNU LGPL, version 2 or later.
* See the COPYING.LIB file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "trace.h"
#include "block/block_int.h"
#include "block/blockjob_int.h"
2016-03-14 11:01:28 +03:00
#include "qapi/error.h"
#include "qapi/qmp/qerror.h"
#include "qemu/ratelimit.h"
#include "sysemu/block-backend.h"
enum {
/*
* Maximum chunk size to feed to copy-on-read. This should be
* large enough to process multiple clusters in a single call, so
* that populating contiguous regions of the image is efficient.
*/
STREAM_CHUNK = 512 * 1024, /* in bytes */
};
typedef struct StreamBlockJob {
BlockJob common;
BlockDriverState *base_overlay; /* COW overlay (stream from this) */
BlockDriverState *above_base; /* Node directly above the base */
BlockdevOnError on_error;
char *backing_file_str;
bool bs_read_only;
bool chain_frozen;
} StreamBlockJob;
static int coroutine_fn stream_populate(BlockBackend *blk,
int64_t offset, uint64_t bytes)
{
assert(bytes < SIZE_MAX);
return blk_co_preadv(blk, offset, bytes, NULL,
BDRV_REQ_COPY_ON_READ | BDRV_REQ_PREFETCH);
}
static void stream_abort(Job *job)
{
StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
if (s->chain_frozen) {
BlockJob *bjob = &s->common;
bdrv_unfreeze_backing_chain(blk_bs(bjob->blk), s->above_base);
}
}
static int stream_prepare(Job *job)
{
StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
BlockJob *bjob = &s->common;
BlockDriverState *bs = blk_bs(bjob->blk);
BlockDriverState *unfiltered_bs = bdrv_skip_filters(bs);
BlockDriverState *base = bdrv_filter_or_cow_bs(s->above_base);
Error *local_err = NULL;
int ret = 0;
bdrv_unfreeze_backing_chain(bs, s->above_base);
s->chain_frozen = false;
if (bdrv_cow_child(unfiltered_bs)) {
const char *base_id = NULL, *base_fmt = NULL;
if (base) {
base_id = s->backing_file_str;
if (base->drv) {
base_fmt = base->drv->format_name;
}
}
bdrv_set_backing_hd(unfiltered_bs, base, &local_err);
ret = bdrv_change_backing_file(unfiltered_bs, base_id, base_fmt, false);
if (local_err) {
error_report_err(local_err);
return -EPERM;
}
}
return ret;
}
static void stream_clean(Job *job)
{
StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
BlockJob *bjob = &s->common;
BlockDriverState *bs = blk_bs(bjob->blk);
/* Reopen the image back in read-only mode if necessary */
if (s->bs_read_only) {
/* Give up write permissions before making it read-only */
blk_set_perm(bjob->blk, 0, BLK_PERM_ALL, &error_abort);
bdrv_reopen_set_read_only(bs, true, NULL);
}
g_free(s->backing_file_str);
}
static int coroutine_fn stream_run(Job *job, Error **errp)
{
StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
BlockBackend *blk = s->common.blk;
BlockDriverState *bs = blk_bs(blk);
BlockDriverState *unfiltered_bs = bdrv_skip_filters(bs);
bool enable_cor = !bdrv_cow_child(s->base_overlay);
int64_t len;
int64_t offset = 0;
Improve block job rate limiting for small bandwidth values ratelimit_calculate_delay() previously reset the accounting every time slice, no matter how much data had been processed before. This had (at least) two consequences: 1. The minimum speed is rather large, e.g. 5 MiB/s for commit and stream. Not sure if there are real-world use cases where this would be a problem. Mirroring and backup over a slow link (e.g. DSL) would come to mind, though. 2. Tests for block job operations (e.g. cancel) were rather racy All block jobs currently use a time slice of 100ms. That's a reasonable value to get smooth output during regular operation. However this also meant that the state of block jobs changed every 100ms, no matter how low the configured limit was. On busy hosts, qemu often transferred additional chunks until the test case had a chance to cancel the job. Fix the block job rate limit code to delay for more than one time slice to address the above issues. To make it easier to handle oversized chunks we switch the semantics from returning a delay _before_ the current request to a delay _after_ the current request. If necessary, this delay consists of multiple time slice units. Since the mirror job sends multiple chunks in one go even if the rate limit was exceeded in between, we need to keep track of the start of the current time slice so we can correctly re-compute the delay for the updated amount of data. The minimum bandwidth now is 1 data unit per time slice. The block jobs are currently passing the amount of data transferred in sectors and using 100ms time slices, so this translates to 5120 bytes/second. With chunk sizes usually being O(512KiB), tests have plenty of time (O(100s)) to operate on block jobs. The chance of a race condition now is fairly remote, except possibly on insanely loaded systems. Signed-off-by: Sascha Silbe <silbe@linux.vnet.ibm.com> Message-id: 1467127721-9564-2-git-send-email-silbe@linux.vnet.ibm.com Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2016-06-28 18:28:41 +03:00
uint64_t delay_ns = 0;
int error = 0;
int64_t n = 0; /* bytes */
if (unfiltered_bs == s->base_overlay) {
/* Nothing to stream */
return 0;
}
len = bdrv_getlength(bs);
if (len < 0) {
return len;
}
job_progress_set_remaining(&s->common.job, len);
/* Turn on copy-on-read for the whole block device so that guest read
* requests help us make progress. Only do this when copying the entire
* backing chain since the copy-on-read operation does not take base into
* account.
*/
if (enable_cor) {
bdrv_enable_copy_on_read(bs);
}
for ( ; offset < len; offset += n) {
bool copy;
int ret;
/* Note that even when no rate limit is applied we need to yield
* with no pending I/O here so that bdrv_drain_all() returns.
*/
job_sleep_ns(&s->common.job, delay_ns);
if (job_is_cancelled(&s->common.job)) {
break;
}
copy = false;
ret = bdrv_is_allocated(unfiltered_bs, offset, STREAM_CHUNK, &n);
if (ret == 1) {
/* Allocated in the top, no need to copy. */
} else if (ret >= 0) {
/* Copy if allocated in the intermediate images. Limit to the
* known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE). */
ret = bdrv_is_allocated_above(bdrv_cow_bs(unfiltered_bs),
s->base_overlay, true,
offset, n, &n);
/* Finish early if end of backing file has been reached */
if (ret == 0 && n == 0) {
n = len - offset;
}
copy = (ret == 1);
}
trace_stream_one_iteration(s, offset, n, ret);
if (copy) {
ret = stream_populate(blk, offset, n);
}
if (ret < 0) {
BlockErrorAction action =
block_job_error_action(&s->common, s->on_error, true, -ret);
if (action == BLOCK_ERROR_ACTION_STOP) {
n = 0;
continue;
}
if (error == 0) {
error = ret;
}
if (action == BLOCK_ERROR_ACTION_REPORT) {
break;
}
}
/* Publish progress */
job_progress_update(&s->common.job, n);
if (copy) {
delay_ns = block_job_ratelimit_get_delay(&s->common, n);
} else {
delay_ns = 0;
Improve block job rate limiting for small bandwidth values ratelimit_calculate_delay() previously reset the accounting every time slice, no matter how much data had been processed before. This had (at least) two consequences: 1. The minimum speed is rather large, e.g. 5 MiB/s for commit and stream. Not sure if there are real-world use cases where this would be a problem. Mirroring and backup over a slow link (e.g. DSL) would come to mind, though. 2. Tests for block job operations (e.g. cancel) were rather racy All block jobs currently use a time slice of 100ms. That's a reasonable value to get smooth output during regular operation. However this also meant that the state of block jobs changed every 100ms, no matter how low the configured limit was. On busy hosts, qemu often transferred additional chunks until the test case had a chance to cancel the job. Fix the block job rate limit code to delay for more than one time slice to address the above issues. To make it easier to handle oversized chunks we switch the semantics from returning a delay _before_ the current request to a delay _after_ the current request. If necessary, this delay consists of multiple time slice units. Since the mirror job sends multiple chunks in one go even if the rate limit was exceeded in between, we need to keep track of the start of the current time slice so we can correctly re-compute the delay for the updated amount of data. The minimum bandwidth now is 1 data unit per time slice. The block jobs are currently passing the amount of data transferred in sectors and using 100ms time slices, so this translates to 5120 bytes/second. With chunk sizes usually being O(512KiB), tests have plenty of time (O(100s)) to operate on block jobs. The chance of a race condition now is fairly remote, except possibly on insanely loaded systems. Signed-off-by: Sascha Silbe <silbe@linux.vnet.ibm.com> Message-id: 1467127721-9564-2-git-send-email-silbe@linux.vnet.ibm.com Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
2016-06-28 18:28:41 +03:00
}
}
if (enable_cor) {
bdrv_disable_copy_on_read(bs);
}
/* Do not remove the backing file if an error was there but ignored. */
return error;
}
static const BlockJobDriver stream_job_driver = {
.job_driver = {
.instance_size = sizeof(StreamBlockJob),
.job_type = JOB_TYPE_STREAM,
.free = block_job_free,
.run = stream_run,
.prepare = stream_prepare,
.abort = stream_abort,
.clean = stream_clean,
.user_resume = block_job_user_resume,
},
};
void stream_start(const char *job_id, BlockDriverState *bs,
BlockDriverState *base, const char *backing_file_str,
int creation_flags, int64_t speed,
BlockdevOnError on_error, Error **errp)
{
StreamBlockJob *s;
BlockDriverState *iter;
bool bs_read_only;
int basic_flags = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
BlockDriverState *base_overlay = bdrv_find_overlay(bs, base);
BlockDriverState *above_base;
if (!base_overlay) {
error_setg(errp, "'%s' is not in the backing chain of '%s'",
base->node_name, bs->node_name);
return;
}
/*
* Find the node directly above @base. @base_overlay is a COW overlay, so
* it must have a bdrv_cow_child(), but it is the immediate overlay of
* @base, so between the two there can only be filters.
*/
above_base = base_overlay;
if (bdrv_cow_bs(above_base) != base) {
above_base = bdrv_cow_bs(above_base);
while (bdrv_filter_bs(above_base) != base) {
above_base = bdrv_filter_bs(above_base);
}
}
if (bdrv_freeze_backing_chain(bs, above_base, errp) < 0) {
return;
}
/* Make sure that the image is opened in read-write mode */
bs_read_only = bdrv_is_read_only(bs);
if (bs_read_only) {
if (bdrv_reopen_set_read_only(bs, false, errp) != 0) {
bs_read_only = false;
goto fail;
}
}
/* Prevent concurrent jobs trying to modify the graph structure here, we
* already have our own plans. Also don't allow resize as the image size is
* queried only at the job start and then cached. */
s = block_job_create(job_id, &stream_job_driver, NULL, bs,
basic_flags | BLK_PERM_GRAPH_MOD,
basic_flags | BLK_PERM_WRITE,
speed, creation_flags, NULL, NULL, errp);
if (!s) {
goto fail;
}
/* Block all intermediate nodes between bs and base, because they will
* disappear from the chain after this operation. The streaming job reads
* every block only once, assuming that it doesn't change, so forbid writes
* and resizes. Reassign the base node pointer because the backing BS of the
* bottom node might change after the call to bdrv_reopen_set_read_only()
* due to parallel block jobs running.
* above_base node might change after the call to
* bdrv_reopen_set_read_only() due to parallel block jobs running.
*/
base = bdrv_filter_or_cow_bs(above_base);
for (iter = bdrv_filter_or_cow_bs(bs); iter != base;
iter = bdrv_filter_or_cow_bs(iter))
{
block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
basic_flags, &error_abort);
}
s->base_overlay = base_overlay;
s->above_base = above_base;
s->backing_file_str = g_strdup(backing_file_str);
s->bs_read_only = bs_read_only;
s->chain_frozen = true;
s->on_error = on_error;
trace_stream_start(bs, base, s);
job_start(&s->common.job);
return;
fail:
if (bs_read_only) {
bdrv_reopen_set_read_only(bs, true, NULL);
}
bdrv_unfreeze_backing_chain(bs, above_base);
}