qemu/block/stream.c
Paolo Bonzini fa4478d5c8 block: wait for job callback in block_job_cancel_sync
The limitation on not having I/O after cancellation cannot really be
kept.  Even streaming has a very small race window where you could
cancel a job and have it report completion.  If this window is hit,
bdrv_change_backing_file() will yield and possibly cause accesses to
dangling pointers etc.

So, let's just assume that we cannot know exactly what will happen
after the coroutine has set busy to false.  We can set a very lax
condition:

- if we cancel the job, the coroutine won't set it to false again
(and hence will not call co_sleep_ns again).

- block_job_cancel_sync will wait for the coroutine to exit, which
pretty much ensures no race.

Instead, we track the coroutine that executes the job and put very
strict conditions on what to do while it is quiescent (busy = false).
First of all, the coroutine must never set busy = false while the job
has been cancelled.  Second, the coroutine can be reentered arbitrarily
while it is quiescent, so you cannot really do anything but co_sleep_ns at
that time.  This condition is obeyed by the block_job_sleep_ns function.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2012-05-10 10:32:12 +02:00

288 lines
7.7 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 "trace.h"
#include "block_int.h"
enum {
/*
* Size of data buffer for populating the image file. This should be large
* enough to process multiple clusters in a single call, so that populating
* contiguous regions of the image is efficient.
*/
STREAM_BUFFER_SIZE = 512 * 1024, /* in bytes */
};
#define SLICE_TIME 100000000ULL /* ns */
typedef struct {
int64_t next_slice_time;
uint64_t slice_quota;
uint64_t dispatched;
} RateLimit;
static int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
{
int64_t delay_ns = 0;
int64_t now = qemu_get_clock_ns(rt_clock);
if (limit->next_slice_time < now) {
limit->next_slice_time = now + SLICE_TIME;
limit->dispatched = 0;
}
if (limit->dispatched + n > limit->slice_quota) {
delay_ns = limit->next_slice_time - now;
} else {
limit->dispatched += n;
}
return delay_ns;
}
static void ratelimit_set_speed(RateLimit *limit, uint64_t speed)
{
limit->slice_quota = speed / (1000000000ULL / SLICE_TIME);
}
typedef struct StreamBlockJob {
BlockJob common;
RateLimit limit;
BlockDriverState *base;
char backing_file_id[1024];
} StreamBlockJob;
static int coroutine_fn stream_populate(BlockDriverState *bs,
int64_t sector_num, int nb_sectors,
void *buf)
{
struct iovec iov = {
.iov_base = buf,
.iov_len = nb_sectors * BDRV_SECTOR_SIZE,
};
QEMUIOVector qiov;
qemu_iovec_init_external(&qiov, &iov, 1);
/* Copy-on-read the unallocated clusters */
return bdrv_co_copy_on_readv(bs, sector_num, nb_sectors, &qiov);
}
static void close_unused_images(BlockDriverState *top, BlockDriverState *base,
const char *base_id)
{
BlockDriverState *intermediate;
intermediate = top->backing_hd;
while (intermediate) {
BlockDriverState *unused;
/* reached base */
if (intermediate == base) {
break;
}
unused = intermediate;
intermediate = intermediate->backing_hd;
unused->backing_hd = NULL;
bdrv_delete(unused);
}
top->backing_hd = base;
}
/*
* Given an image chain: [BASE] -> [INTER1] -> [INTER2] -> [TOP]
*
* Return true if the given sector is allocated in top.
* Return false if the given sector is allocated in intermediate images.
* Return true otherwise.
*
* 'pnum' is set to the number of sectors (including and immediately following
* the specified sector) that are known to be in the same
* allocated/unallocated state.
*
*/
static int coroutine_fn is_allocated_base(BlockDriverState *top,
BlockDriverState *base,
int64_t sector_num,
int nb_sectors, int *pnum)
{
BlockDriverState *intermediate;
int ret, n;
ret = bdrv_co_is_allocated(top, sector_num, nb_sectors, &n);
if (ret) {
*pnum = n;
return ret;
}
/*
* Is the unallocated chunk [sector_num, n] also
* unallocated between base and top?
*/
intermediate = top->backing_hd;
while (intermediate) {
int pnum_inter;
/* reached base */
if (intermediate == base) {
*pnum = n;
return 1;
}
ret = bdrv_co_is_allocated(intermediate, sector_num, nb_sectors,
&pnum_inter);
if (ret < 0) {
return ret;
} else if (ret) {
*pnum = pnum_inter;
return 0;
}
/*
* [sector_num, nb_sectors] is unallocated on top but intermediate
* might have
*
* [sector_num+x, nr_sectors] allocated.
*/
if (n > pnum_inter) {
n = pnum_inter;
}
intermediate = intermediate->backing_hd;
}
return 1;
}
static void coroutine_fn stream_run(void *opaque)
{
StreamBlockJob *s = opaque;
BlockDriverState *bs = s->common.bs;
BlockDriverState *base = s->base;
int64_t sector_num, end;
int ret = 0;
int n;
void *buf;
s->common.len = bdrv_getlength(bs);
if (s->common.len < 0) {
block_job_complete(&s->common, s->common.len);
return;
}
end = s->common.len >> BDRV_SECTOR_BITS;
buf = qemu_blockalign(bs, STREAM_BUFFER_SIZE);
/* 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 (!base) {
bdrv_enable_copy_on_read(bs);
}
for (sector_num = 0; sector_num < end; sector_num += n) {
uint64_t delay_ns = 0;
wait:
/* Note that even when no rate limit is applied we need to yield
* with no pending I/O here so that qemu_aio_flush() returns.
*/
block_job_sleep_ns(&s->common, rt_clock, delay_ns);
if (block_job_is_cancelled(&s->common)) {
break;
}
if (base) {
ret = is_allocated_base(bs, base, sector_num,
STREAM_BUFFER_SIZE / BDRV_SECTOR_SIZE, &n);
} else {
ret = bdrv_co_is_allocated(bs, sector_num,
STREAM_BUFFER_SIZE / BDRV_SECTOR_SIZE,
&n);
}
trace_stream_one_iteration(s, sector_num, n, ret);
if (ret == 0) {
if (s->common.speed) {
delay_ns = ratelimit_calculate_delay(&s->limit, n);
if (delay_ns > 0) {
goto wait;
}
}
ret = stream_populate(bs, sector_num, n, buf);
}
if (ret < 0) {
break;
}
ret = 0;
/* Publish progress */
s->common.offset += n * BDRV_SECTOR_SIZE;
}
if (!base) {
bdrv_disable_copy_on_read(bs);
}
if (!block_job_is_cancelled(&s->common) && sector_num == end && ret == 0) {
const char *base_id = NULL;
if (base) {
base_id = s->backing_file_id;
}
ret = bdrv_change_backing_file(bs, base_id, NULL);
close_unused_images(bs, base, base_id);
}
qemu_vfree(buf);
block_job_complete(&s->common, ret);
}
static void stream_set_speed(BlockJob *job, int64_t speed, Error **errp)
{
StreamBlockJob *s = container_of(job, StreamBlockJob, common);
if (speed < 0) {
error_set(errp, QERR_INVALID_PARAMETER, "speed");
return;
}
ratelimit_set_speed(&s->limit, speed / BDRV_SECTOR_SIZE);
}
static BlockJobType stream_job_type = {
.instance_size = sizeof(StreamBlockJob),
.job_type = "stream",
.set_speed = stream_set_speed,
};
void stream_start(BlockDriverState *bs, BlockDriverState *base,
const char *base_id, int64_t speed,
BlockDriverCompletionFunc *cb,
void *opaque, Error **errp)
{
StreamBlockJob *s;
s = block_job_create(&stream_job_type, bs, speed, cb, opaque, errp);
if (!s) {
return;
}
s->base = base;
if (base_id) {
pstrcpy(s->backing_file_id, sizeof(s->backing_file_id), base_id);
}
s->common.co = qemu_coroutine_create(stream_run);
trace_stream_start(bs, base, s, s->common.co, opaque);
qemu_coroutine_enter(s->common.co, s);
}