qemu/block/stream.c
Max Reitz 67acfd2188 stream: Deal with filters
Because of the (not so recent anymore) changes that make the stream job
independent of the base node and instead track the node above it, we
have to split that "bottom" node into two cases: The bottom COW node,
and the node directly above the base node (which may be an R/W filter
or the bottom COW node).

Signed-off-by: Max Reitz <mreitz@redhat.com>
2020-09-07 12:31:31 +02:00

310 lines
9.6 KiB
C

/*
* 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"
#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;
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;
}
}
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);
}