qemu/block/stream.c
Chen Qun 35c9453592 block/stream: Remove redundant statement in stream_run()
Clang static code analyzer show warning:
  block/stream.c:186:9: warning: Value stored to 'ret' is never read
        ret = 0;
        ^     ~
Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Chen Qun <kuhn.chenqun@huawei.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200302130715.29440-3-kuhn.chenqun@huawei.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
2020-03-09 15:59:31 +01:00

281 lines
8.4 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 *bottom;
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->bottom);
}
}
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 *base = backing_bs(s->bottom);
Error *local_err = NULL;
int ret = 0;
bdrv_unfreeze_backing_chain(bs, s->bottom);
s->chain_frozen = false;
if (bs->backing) {
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(bs, base, &local_err);
ret = bdrv_change_backing_file(bs, base_id, base_fmt);
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);
bool enable_cor = !backing_bs(s->bottom);
int64_t len;
int64_t offset = 0;
uint64_t delay_ns = 0;
int error = 0;
int64_t n = 0; /* bytes */
if (bs == s->bottom) {
/* 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(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(backing_bs(bs), s->bottom, 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 *bottom = bdrv_find_overlay(bs, base);
if (bdrv_freeze_backing_chain(bs, bottom, 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.
*/
base = backing_bs(bottom);
for (iter = backing_bs(bs); iter && iter != base; iter = backing_bs(iter)) {
block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
basic_flags, &error_abort);
}
s->bottom = bottom;
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, bottom);
}