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Re: [Qemu-devel] [PATCH 08/15] qmp: add block_stream command
From: |
Marcelo Tosatti |
Subject: |
Re: [Qemu-devel] [PATCH 08/15] qmp: add block_stream command |
Date: |
Thu, 28 Jul 2011 12:53:41 -0300 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, Jul 27, 2011 at 02:44:48PM +0100, Stefan Hajnoczi wrote:
> For leaf images with copy-on-read semantics, the stream command allows
> the user to populate the image file by copying data from the backing
> file while the guest is running. Once all blocks have been streamed,
> the dependency on the original backing file is removed. Therefore,
> stream commands can be used to implement post-copy live block migration
> and rapid deployment.
>
> The command synopsis is:
>
> block_stream
> ------------
>
> Copy data from a backing file into a block device.
>
> The block streaming operation is performed in the background until the
> entire backing file has been copied. This command returns immediately
> once streaming has started. The status of ongoing block streaming
> operations can be checked with query-block-jobs. The operation can be
> stopped before it has completed using the block_job_cancel command.
>
> If a base file is specified then sectors are not copied from that base
> file and its backing chain. When streaming completes the image file
> will have the base file as its backing file. This can be used to stream
> a subset of the backing file chain instead of flattening the entire
> image.
>
> On successful completion the image file is updated to drop the backing
> file.
>
> Arguments:
>
> - device: device name (json-string)
> - base: common backing file (json-string, optional)
>
> Errors:
>
> DeviceInUse: streaming is already active on this device
> DeviceNotFound: device name is invalid
> NotSupported: image streaming is not supported by this device
>
> Events:
>
> On completion the BLOCK_JOB_COMPLETED event is raised with the following
> fields:
>
> - type: job type ("stream" for image streaming, json-string)
> - device: device name (json-string)
> - end: maximum progress value (json-int)
> - position: current progress value (json-int)
> - speed: rate limit, bytes per second (json-int)
> - error: error message (json-string, only on error)
>
> The completion event is raised both on success and on failure. On
> success position is equal to end. On failure position and end can be
> used to indicate at which point the operation failed.
>
> On failure the error field contains a human-readable error message.
> There are no semantics other than that streaming has failed and clients
> should not try to interpret the error string.
>
> Examples:
>
> -> { "execute": "block_stream", "arguments": { "device": "virtio0" } }
> <- { "return": {} }
>
> Signed-off-by: Adam Litke <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
> blockdev.c | 133
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> blockdev.h | 1 +
> hmp-commands.hx | 14 ++++++
> monitor.c | 3 +
> monitor.h | 1 +
> qerror.c | 8 +++
> qerror.h | 6 +++
> qmp-commands.hx | 64 ++++++++++++++++++++++++++
> 8 files changed, 230 insertions(+), 0 deletions(-)
>
> diff --git a/blockdev.c b/blockdev.c
> index b337732..cd5e49c 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -16,6 +16,7 @@
> #include "sysemu.h"
> #include "hw/qdev.h"
> #include "block_int.h"
> +#include "qjson.h"
>
> static QTAILQ_HEAD(drivelist, DriveInfo) drives =
> QTAILQ_HEAD_INITIALIZER(drives);
>
> @@ -50,6 +51,131 @@ static const int if_max_devs[IF_COUNT] = {
> [IF_SCSI] = 7,
> };
>
> +typedef struct StreamState {
> + int64_t offset; /* current position in block device */
> + BlockDriverState *bs;
> + QEMUTimer *timer;
> + QLIST_ENTRY(StreamState) list;
> +} StreamState;
> +
> +static QLIST_HEAD(, StreamState) block_streams =
> + QLIST_HEAD_INITIALIZER(block_streams);
> +
> +static QObject *stream_get_qobject(StreamState *s)
> +{
> + const char *name = bdrv_get_device_name(s->bs);
> + int64_t len = bdrv_getlength(s->bs);
> +
> + return qobject_from_jsonf("{ 'device': %s, 'type': 'stream', "
> + "'offset': %" PRId64 ", 'len': %" PRId64 ", "
> + "'speed': %" PRId64 " }",
> + name, s->offset, len, (int64_t)0);
> +}
> +
> +static void stream_mon_event(StreamState *s, int ret)
> +{
> + QObject *data = stream_get_qobject(s);
> +
> + if (ret < 0) {
> + QDict *qdict = qobject_to_qdict(data);
> +
> + qdict_put(qdict, "error", qstring_from_str(strerror(-ret)));
> + }
> +
> + monitor_protocol_event(QEVENT_BLOCK_JOB_COMPLETED, data);
> + qobject_decref(data);
> +}
> +
> +static void stream_free(StreamState *s)
> +{
> + QLIST_REMOVE(s, list);
> +
> + qemu_del_timer(s->timer);
> + qemu_free_timer(s->timer);
> + qemu_free(s);
> +}
> +
> +static void stream_complete(StreamState *s, int ret)
> +{
> + stream_mon_event(s, ret);
> + stream_free(s);
> +}
> +
> +static void stream_cb(void *opaque, int nb_sectors)
> +{
> + StreamState *s = opaque;
> +
> + if (nb_sectors < 0) {
> + stream_complete(s, nb_sectors);
> + return;
> + }
> +
> + s->offset += nb_sectors * BDRV_SECTOR_SIZE;
> +
> + if (s->offset == bdrv_getlength(s->bs)) {
> + bdrv_change_backing_file(s->bs, NULL, NULL);
> + stream_complete(s, 0);
> + } else {
> + qemu_mod_timer(s->timer, qemu_get_clock_ns(rt_clock));
> + }
> +}
> +
> +/* We can't call bdrv_aio_stream() directly from the callback because that
> + * makes qemu_aio_flush() not complete until the streaming is completed.
> + * By delaying with a timer, we give qemu_aio_flush() a chance to complete.
> + */
> +static void stream_next_iteration(void *opaque)
> +{
> + StreamState *s = opaque;
> +
> + bdrv_aio_copy_backing(s->bs, s->offset / BDRV_SECTOR_SIZE, stream_cb, s);
> +}
The plan is to replace format specific code with the generic
implementation in the future?
> +
> +static StreamState *stream_find(const char *device)
> +{
> + StreamState *s;
> +
> + QLIST_FOREACH(s, &block_streams, list) {
> + if (strcmp(bdrv_get_device_name(s->bs), device) == 0) {
> + return s;
> + }
> + }
> + return NULL;
> +}
> +
> +static StreamState *stream_start(const char *device)
> +{
> + StreamState *s;
> + BlockDriverAIOCB *acb;
> + BlockDriverState *bs;
> +
> + s = stream_find(device);
> + if (s) {
> + qerror_report(QERR_DEVICE_IN_USE, device);
> + return NULL;
> + }
> +
> + bs = bdrv_find(device);
> + if (!bs) {
> + qerror_report(QERR_DEVICE_NOT_FOUND, device);
> + return NULL;
> + }
> +
> + s = qemu_mallocz(sizeof(*s));
> + s->bs = bs;
> + s->timer = qemu_new_timer_ns(rt_clock, stream_next_iteration, s);
> + QLIST_INSERT_HEAD(&block_streams, s, list);
Should increase refcount with drive_get_ref().
- [Qemu-devel] [PATCH 05/15] qed: add support for copy-on-read, (continued)
- [Qemu-devel] [PATCH 05/15] qed: add support for copy-on-read, Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 03/15] qed: extract qed_start_allocating_write(), Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 10/15] qmp: add query-block-jobs command, Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 09/15] qmp: add block_job_cancel command, Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 06/15] qed: avoid deadlock on emulated synchronous I/O, Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 02/15] qed: replace is_write with flags field, Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 04/15] qed: make qed_aio_write_alloc() reusable, Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 11/15] qmp: add block_job_set_speed command, Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 07/15] block: add bdrv_aio_copy_backing(), Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 08/15] qmp: add block_stream command, Stefan Hajnoczi, 2011/07/27
- Re: [Qemu-devel] [PATCH 08/15] qmp: add block_stream command,
Marcelo Tosatti <=
- [Qemu-devel] [PATCH 01/15] block: add -drive copy-on-read=on|off, Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 13/15] qed: intelligent streaming implementation, Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 12/15] block: add -drive stream=on|off, Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 15/15] tests: add image streaming QMP interface tests, Stefan Hajnoczi, 2011/07/27
- [Qemu-devel] [PATCH 14/15] trace: trace bdrv_aio_readv/writev error paths, Stefan Hajnoczi, 2011/07/27