Re: [Qemu-devel] [PATCH V2 1/2] Implement sync modes for drive-backup.

[Fam Zheng <famz@redhat.com>]

Great work! The patch looks good for me, I made two trivial style
comments (if you respin, you can check your patches for style problems
by running scripts/checkpatch.pl).

On Fri, 07/05 18:35, Ian Main wrote:
> This patch adds sync-modes to the drive-backup interface and
> implements the FULL, NONE and TOP modes of synchronization.
> 
> FULL performs as before copying the entire contents of the drive
> while preserving the point-in-time using CoW.
> NONE only copies new writes to the target drive.
> TOP copies changes to the topmost drive image and preserves the
> point-in-time using CoW.
> 
> Signed-off-by: Ian Main <imain@redhat.com>
> ---
>  block/backup.c            | 90 +++++++++++++++++++++++++++++++----------------
>  blockdev.c                | 25 ++++++++-----
>  include/block/block_int.h |  4 ++-
>  qapi-schema.json          |  4 +++
>  qmp-commands.hx           |  1 +
>  5 files changed, 85 insertions(+), 39 deletions(-)
> 
> diff --git a/block/backup.c b/block/backup.c
> index 16105d4..e72a5af 100644
> --- a/block/backup.c
> +++ b/block/backup.c
> @@ -37,6 +37,7 @@ typedef struct CowRequest {
>  typedef struct BackupBlockJob {
>      BlockJob common;
>      BlockDriverState *target;
> +    MirrorSyncMode sync_mode;
>      RateLimit limit;
>      BlockdevOnError on_source_error;
>      BlockdevOnError on_target_error;
> @@ -247,40 +248,68 @@ static void coroutine_fn backup_run(void *opaque)
>  
>      bdrv_add_before_write_notifier(bs, &before_write);
>  
> -    for (; start < end; start++) {
> -        bool error_is_read;
> -
> -        if (block_job_is_cancelled(&job->common)) {
> -            break;
> +    if (job->sync_mode == MIRROR_SYNC_MODE_NONE) {
> +        while (!block_job_is_cancelled(&job->common)) {
> +            /* Yield until the job is cancelled.  We just let our before_write
> +             * notify callback service CoW requests. */
> +            job->common.busy = false;
> +            qemu_coroutine_yield();
> +            job->common.busy = true;
>          }
> +    } else {
> +        /* Both FULL and TOP SYNC_MODE's require copying.. */
> +        for (; start < end; start++) {
> +            bool error_is_read;
>  
> -        /* we need to yield so that qemu_aio_flush() returns.
> -         * (without, VM does not reboot)
> -         */
> -        if (job->common.speed) {
> -            uint64_t delay_ns = ratelimit_calculate_delay(
> -                &job->limit, job->sectors_read);
> -            job->sectors_read = 0;
> -            block_job_sleep_ns(&job->common, rt_clock, delay_ns);
> -        } else {
> -            block_job_sleep_ns(&job->common, rt_clock, 0);
> -        }
> +            if (block_job_is_cancelled(&job->common)) {
> +                break;
> +            }
>  
> -        if (block_job_is_cancelled(&job->common)) {
> -            break;
> -        }
> +            /* we need to yield so that qemu_aio_flush() returns.
> +             * (without, VM does not reboot)
> +             */
> +            if (job->common.speed) {
> +                uint64_t delay_ns = ratelimit_calculate_delay(
> +                        &job->limit, job->sectors_read);
> +                job->sectors_read = 0;
> +                block_job_sleep_ns(&job->common, rt_clock, delay_ns);
> +            } else {
> +                block_job_sleep_ns(&job->common, rt_clock, 0);
> +            }
>  
> -        ret = backup_do_cow(bs, start * BACKUP_SECTORS_PER_CLUSTER,
> -                            BACKUP_SECTORS_PER_CLUSTER, &error_is_read);
> -        if (ret < 0) {
> -            /* Depending on error action, fail now or retry cluster */
> -            BlockErrorAction action =
> -                backup_error_action(job, error_is_read, -ret);
> -            if (action == BDRV_ACTION_REPORT) {
> +            if (block_job_is_cancelled(&job->common)) {
>                  break;
> -            } else {
> -                start--;
> -                continue;
> +            }
> +
> +            if (job->sync_mode == MIRROR_SYNC_MODE_TOP) {
> +                int n, alloced;
> +
> +                /* Check to see if these blocks are already in the backing file. */
line over 80 characters
> +
> +                alloced =
> +                    bdrv_co_is_allocated(bs, start * BACKUP_SECTORS_PER_CLUSTER,
> +                                         BACKUP_SECTORS_PER_CLUSTER, &n);
> +                /* The above call returns true if the given sector is in the
> +                 * topmost image.  If that is the case then we must copy it as
> +                 * it has been modified from the original backing file. 
Trailing whitespace.

Thanks

-- 
Fam