Am 24.07.2012 13:04, schrieb Paolo Bonzini:
> This patch adds the implementation of a new job that mirrors a disk to
> a new image while letting the guest continue using the old image.
> The target is treated as a "black box" and data is copied from the
> source to the target in the background. This can be used for several
> purposes, including storage migration, continuous replication, and
> observation of the guest I/O in an external program. It is also a
> first step in replacing the inefficient block migration code that is
> part of QEMU.
>
> The job is possibly never-ending, but it is logically structured into
> two phases: 1) copy all data as fast as possible until the target
> first gets in sync with the source; 2) keep target in sync and
> ensure that reopening to the target gets a correct (full) copy
> of the source data.
>
> The second phase is indicated by the progress in "info block-jobs"
> reporting the current offset to be equal to the length of the file.
> When the job is cancelled in the second phase, QEMU will run the
> job until the source is clean and quiescent, then it will report
> successful completion of the job.
>
> In other words, the BLOCK_JOB_CANCELLED event means that the target
> may _not_ be consistent with a past state of the source; the
> BLOCK_JOB_COMPLETED event means that the target is consistent with
> a past state of the source. (Note that it could already happen
> that management lost the race against QEMU and got a completion
> event instead of cancellation).
>
> It is not yet possible to complete the job and switch over to the target
> disk. The next patches will fix this and add many refinements to the
> basic idea introduced here. These include improved error management,
> some tunable knobs and performance optimizations.
>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> block/Makefile.objs | 2 +-
> block/mirror.c | 232
> +++++++++++++++++++++++++++++++++++++++++++++++++++
> block_int.h | 20 +++++
> qapi-schema.json | 17 ++++
> trace-events | 7 ++
> 5 files changed, 277 insertions(+), 1 deletion(-)
> create mode 100644 block/mirror.c
>
> diff --git a/block/Makefile.objs b/block/Makefile.objs
> index c45affc..f1a394a 100644
> --- a/block/Makefile.objs
> +++ b/block/Makefile.objs
> @@ -9,4 +9,4 @@ block-obj-$(CONFIG_LIBISCSI) += iscsi.o
> block-obj-$(CONFIG_CURL) += curl.o
> block-obj-$(CONFIG_RBD) += rbd.o
>
> -common-obj-y += stream.o
> +common-obj-y += stream.o mirror.o
> diff --git a/block/mirror.c b/block/mirror.c
> new file mode 100644
> index 0000000..f7d36f9
> --- /dev/null
> +++ b/block/mirror.c
> @@ -0,0 +1,232 @@
> +/*
> + * Image mirroring
> + *
> + * Copyright Red Hat, Inc. 2012
> + *
> + * Authors:
> + * Paolo Bonzini <pbonz...@redhat.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 "blockjob.h"
> +#include "block_int.h"
> +#include "qemu/ratelimit.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.
> + */
> + BLOCK_SIZE = 512 * BDRV_SECTORS_PER_DIRTY_CHUNK, /* in bytes */
> +};
> +
> +#define SLICE_TIME 100000000ULL /* ns */
> +
> +typedef struct MirrorBlockJob {
> + BlockJob common;
> + RateLimit limit;
> + BlockDriverState *target;
> + MirrorSyncMode mode;
> + int64_t sector_num;
> + uint8_t *buf;
> +} MirrorBlockJob;
> +
> +static int coroutine_fn mirror_iteration(MirrorBlockJob *s)
> +{
> + BlockDriverState *source = s->common.bs;
> + BlockDriverState *target = s->target;
> + QEMUIOVector qiov;
> + int ret, nb_sectors;
> + int64_t end;
> + struct iovec iov;
> +
> + end = s->common.len >> BDRV_SECTOR_BITS;
> + s->sector_num = bdrv_get_next_dirty(source, s->sector_num);
> + nb_sectors = MIN(BDRV_SECTORS_PER_DIRTY_CHUNK, end - s->sector_num);
> + bdrv_reset_dirty(source, s->sector_num, nb_sectors);
> +
> + /* Copy the dirty cluster. */
> + iov.iov_base = s->buf;
> + iov.iov_len = nb_sectors * 512;
> + qemu_iovec_init_external(&qiov, &iov, 1);
> +
> + trace_mirror_one_iteration(s, s->sector_num, nb_sectors);
> + ret = bdrv_co_readv(source, s->sector_num, nb_sectors, &qiov);
> + if (ret < 0) {
> + return ret;
> + }
> + return bdrv_co_writev(target, s->sector_num, nb_sectors, &qiov);
> +}
> +
> +static void coroutine_fn mirror_run(void *opaque)
> +{
> + MirrorBlockJob *s = opaque;
> + BlockDriverState *bs = s->common.bs;
> + int64_t sector_num, end;
> + int ret = 0;
> + int n;
> + bool synced = false;
> +
> + if (block_job_is_cancelled(&s->common)) {
> + goto immediate_exit;
> + }
> +
> + s->common.len = bdrv_getlength(bs);
> + if (s->common.len < 0) {
> + block_job_completed(&s->common, s->common.len);
> + return;
> + }
> +
> + end = s->common.len >> BDRV_SECTOR_BITS;
> + s->buf = qemu_blockalign(bs, BLOCK_SIZE);
> +
> + if (s->mode == MIRROR_SYNC_MODE_FULL || s->mode == MIRROR_SYNC_MODE_TOP)
> {
I think this is the common case, so s->mode != MIRROR_SYNC_MODE_NONE
might describe it better?
> + /* First part, loop on the sectors and initialize the dirty bitmap.
> */
> + BlockDriverState *base;
> + base = s->mode == MIRROR_SYNC_MODE_FULL ? NULL : bs->backing_hd;
> + for (sector_num = 0; sector_num < end; ) {
> + int64_t next = (sector_num | (BDRV_SECTORS_PER_DIRTY_CHUNK - 1))
> + 1;
> + ret = bdrv_co_is_allocated_above(bs, base,
> + sector_num, next - sector_num,
> &n);
> +
> + if (ret < 0) {
> + break;
> + } else if (ret == 1) {
> + bdrv_set_dirty(bs, sector_num, n);
> + sector_num = next;
> + } else {
> + sector_num += n;
> + }
Maybe it would be worth checking for n == 0 and returning an error in
that case. One example where this happens is when asking for the
allocation status after EOF. It shouldn't happen as long as
bdrv_truncate() is forbidden while the job runs, but an extra check
rarely hurts.
> + }
> + }
> +
> + if (ret < 0) {
> + goto immediate_exit;
> + }
Why not do that directly instead of having a break; first just to get here?
> +
> + s->sector_num = -1;
> + for (;;) {
> + uint64_t delay_ns;
> + int64_t cnt;
> + bool should_complete;
> +
> + cnt = bdrv_get_dirty_count(bs);
> + if (cnt != 0) {
> + ret = mirror_iteration(s);
> + if (ret < 0) {
> + break;
goto immediate_exit? It's the same now, but code after the loop may be
added in the future.
> + }
> + cnt = bdrv_get_dirty_count(bs);
> + }
> +
> + if (cnt != 0) {
> + should_complete = false;
> + } else {
> + trace_mirror_before_flush(s);
> + bdrv_flush(s->target);
No error handling?
Kevin
