Re: [Qemu-devel] [PATCH v12 07/17] qmp: Add support of "dirty-bitmap" sync mode for drive-backup

[John Snow <jsnow@redhat.com>]

On 02/11/2015 12:47 PM, Max Reitz wrote:
> On 2015-02-09 at 20:35, John Snow wrote:
>> For "dirty-bitmap" sync mode, the block job will iterate through the
>> given dirty bitmap to decide if a sector needs backup (backup all the
>> dirty clusters and skip clean ones), just as allocation conditions of
>> "top" sync mode.
>>
>> Signed-off-by: Fam Zheng <famz@redhat.com>
>> Signed-off-by: John Snow <jsnow@redhat.com>
>> ---
>>   block.c                   |   9 +++
>>   block/backup.c            | 149
>> +++++++++++++++++++++++++++++++++++++++-------
>>   block/mirror.c            |   4 ++
>>   blockdev.c                |  18 +++++-
>>   hmp.c                     |   3 +-
>>   include/block/block.h     |   1 +
>>   include/block/block_int.h |   2 +
>>   qapi/block-core.json      |  13 ++--
>>   qmp-commands.hx           |   7 ++-
>>   9 files changed, 172 insertions(+), 34 deletions(-)
>>
>> diff --git a/block.c b/block.c
>> index 8d84ace..e93fceb 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -5648,6 +5648,15 @@ static void bdrv_reset_dirty(BlockDriverState
>> *bs, int64_t cur_sector,
>>       }
>>   }
>> +/**
>> + * Advance an HBitmapIter to an arbitrary offset.
>> + */
>> +void bdrv_set_dirty_iter(HBitmapIter *hbi, int64_t offset)
>> +{
>> +    assert(hbi->hb);
>> +    hbitmap_iter_init(hbi, hbi->hb, offset);
>> +}
>> +
>>   int64_t bdrv_get_dirty_count(BlockDriverState *bs, BdrvDirtyBitmap
>> *bitmap)
>>   {
>>       return hbitmap_count(bitmap->bitmap);
>> diff --git a/block/backup.c b/block/backup.c
>> index 1c535b1..bf8c0e7 100644
>> --- a/block/backup.c
>> +++ b/block/backup.c
>> @@ -37,6 +37,8 @@ typedef struct CowRequest {
>>   typedef struct BackupBlockJob {
>>       BlockJob common;
>>       BlockDriverState *target;
>> +    /* bitmap for sync=dirty-bitmap */
>> +    BdrvDirtyBitmap *sync_bitmap;
>>       MirrorSyncMode sync_mode;
>>       RateLimit limit;
>>       BlockdevOnError on_source_error;
>> @@ -242,6 +244,31 @@ static void backup_complete(BlockJob *job, void
>> *opaque)
>>       g_free(data);
>>   }
>> +static bool coroutine_fn yield_and_check(BackupBlockJob *job)
>> +{
>> +    if (block_job_is_cancelled(&job->common)) {
>> +        return true;
>> +    }
>> +
>> +    /* 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, QEMU_CLOCK_REALTIME, delay_ns);
>> +    } else {
>> +        block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, 0);
>> +    }
>> +
>> +    if (block_job_is_cancelled(&job->common)) {
>> +        return true;
>> +    }
>> +
>> +    return false;
>> +}
>> +
>>   static void coroutine_fn backup_run(void *opaque)
>>   {
>>       BackupBlockJob *job = opaque;
>> @@ -254,13 +281,13 @@ static void coroutine_fn backup_run(void *opaque)
>>       };
>>       int64_t start, end;
>>       int ret = 0;
>> +    bool error_is_read;
>>       QLIST_INIT(&job->inflight_reqs);
>>       qemu_co_rwlock_init(&job->flush_rwlock);
>>       start = 0;
>> -    end = DIV_ROUND_UP(job->common.len / BDRV_SECTOR_SIZE,
>> -                       BACKUP_SECTORS_PER_CLUSTER);
>> +    end = DIV_ROUND_UP(job->common.len, BACKUP_CLUSTER_SIZE);
>>       job->bitmap = hbitmap_alloc(end, 0);
>> @@ -278,28 +305,61 @@ static void coroutine_fn backup_run(void *opaque)
>>               qemu_coroutine_yield();
>>               job->common.busy = true;
>>           }
>> +    } else if (job->sync_mode == MIRROR_SYNC_MODE_DIRTY_BITMAP) {
>> +        /* Dirty Bitmap sync has a slightly different iteration
>> method */
>> +        HBitmapIter hbi;
>> +        int64_t sector;
>> +        int64_t cluster;
>> +        int64_t last_cluster = -1;
>> +        bool polyrhythmic;
>> +
>> +        bdrv_dirty_iter_init(bs, job->sync_bitmap, &hbi);
>> +        /* Does the granularity happen to match our backup cluster
>> size? */
>> +        polyrhythmic =
>> (bdrv_dirty_bitmap_granularity(job->sync_bitmap) !=
>> +                        BACKUP_CLUSTER_SIZE);
>> +
>> +        /* Find the next dirty /sector/ and copy that /cluster/ */
>> +        while ((sector = hbitmap_iter_next(&hbi)) != -1) {
>> +            if (yield_and_check(job)) {
>> +                goto leave;
>> +            }
>> +            cluster = sector / BACKUP_SECTORS_PER_CLUSTER;
>> +
>> +            /* Play some catchup with the progress meter */
>> +            if (cluster != last_cluster + 1) {
>> +                job->common.offset += ((cluster - last_cluster - 1) *
>> +                                       BACKUP_CLUSTER_SIZE);
>> +            }
>
> I guess the "- 1" in the calculation comes from backup_do_cow()
> modifying job->common.offset, too. How about simply overwriting it like
> "job->common.offset = cluster * BACKUP_CLUSTER_SIZE"? And it may be a
> good idea to move this update above yield_and_check() because that's the
> progress we have actually done up to that point (and I imagine
> yield_and_check() is the point where the caller might check the progress).
>

Yes: If the last cluster we wrote out was 2, and we're on 4 now, we only 
need to make up for #3, because #4 will be handled in the usual ways.

I don't know how wise this was, but I wanted to only "fake" progress 
updates for clusters I *know* I skipped in incremental backups, so I 
wanted to make sure the math worked out. Just overwriting the progress 
seemed like cheating a little, I guess ...

It was kind of just a "testing thing" to just do the additions and see 
if the math checked out in the end. You may notice that unlike Fam's 
iotests, I leave the progress checks enabled for my tests.

Putting it above the cancellation check does make sense, though. I 
didn't test cancellations as well as I ought have.

>> +
>> +            do {
>> +                ret = backup_do_cow(bs, cluster *
>> BACKUP_SECTORS_PER_CLUSTER,
>> +                                    BACKUP_SECTORS_PER_CLUSTER,
>> &error_is_read);
>> +                if ((ret < 0) &&
>> +                    backup_error_action(job, error_is_read, -ret) ==
>> +                    BLOCK_ERROR_ACTION_REPORT) {
>> +                    goto leave;
>> +                }
>> +            } while (ret < 0);
>> +
>> +            /* Advance (or rewind) our iterator if we need to. */
>> +            if (polyrhythmic) {
>> +                bdrv_set_dirty_iter(&hbi,
>> +                                    (cluster + 1) *
>> BACKUP_SECTORS_PER_CLUSTER);
>> +            }
>> +
>> +            last_cluster = cluster;
>> +        }
>> +
>> +        /* Play some final catchup with the progress meter */
>> +        if (last_cluster + 1 < end) {
>> +            job->common.offset += ((end - last_cluster - 1) *
>> +                                   BACKUP_CLUSTER_SIZE);
>> +        }
>> +
>
> Superfluous empty line.
>
>>       } else {
>>           /* Both FULL and TOP SYNC_MODE's require copying.. */
>>           for (; start < end; start++) {
>> -            bool error_is_read;
>> -
>> -            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, QEMU_CLOCK_REALTIME,
>> delay_ns);
>> -            } else {
>> -                block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME,
>> 0);
>> -            }
>> -
>> -            if (block_job_is_cancelled(&job->common)) {
>> +            if (yield_and_check(job)) {
>>                   break;
>>               }
>> @@ -351,12 +411,26 @@ static void coroutine_fn backup_run(void *opaque)
>>           }
>>       }
>> +leave:
>>       notifier_with_return_remove(&before_write);
>>       /* wait until pending backup_do_cow() calls have completed */
>>       qemu_co_rwlock_wrlock(&job->flush_rwlock);
>>       qemu_co_rwlock_unlock(&job->flush_rwlock);
>> +    if (job->sync_bitmap) {
>> +        BdrvDirtyBitmap *bm;
>> +        if (ret < 0) {
>> +            /* Merge the successor back into the parent, delete
>> nothing. */
>> +            bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
>> +            assert(bm);
>> +            bdrv_enable_dirty_bitmap(job->sync_bitmap);
>> +        } else {
>> +            /* Everything is fine, delete this bitmap and install the
>> backup. */
>> +            bm = bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL);
>> +            assert(bm);
>> +        }
>> +    }
>>       hbitmap_free(job->bitmap);
>>       bdrv_iostatus_disable(target);
>> @@ -369,6 +443,7 @@ static void coroutine_fn backup_run(void *opaque)
>>   void backup_start(BlockDriverState *bs, BlockDriverState *target,
>>                     int64_t speed, MirrorSyncMode sync_mode,
>> +                  BdrvDirtyBitmap *sync_bitmap,
>>                     BlockdevOnError on_source_error,
>>                     BlockdevOnError on_target_error,
>>                     BlockCompletionFunc *cb, void *opaque,
>> @@ -412,17 +487,37 @@ void backup_start(BlockDriverState *bs,
>> BlockDriverState *target,
>>           return;
>>       }
>> +    if (sync_mode == MIRROR_SYNC_MODE_DIRTY_BITMAP) {
>> +        if (!sync_bitmap) {
>> +            error_setg(errp, "must provide a valid bitmap name for "
>> +                             "\"dirty-bitmap\" sync mode");
>> +            return;
>> +        }
>> +
>> +        /* Create a new bitmap, and freeze/disable this one. */
>> +        if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp)
>> < 0) {
>> +            return;
>> +        }
>> +
>
> Another superfluous empty line.
>
>> +    } else if (sync_bitmap) {
>> +        error_setg(errp,
>> +                   "a sync_bitmap was provided to backup_run, "
>> +                   "but received an incompatible sync_mode (%s)",
>> +                   MirrorSyncMode_lookup[sync_mode]);
>> +        return;
>> +    }
>> +
>>       len = bdrv_getlength(bs);
>>       if (len < 0) {
>>           error_setg_errno(errp, -len, "unable to get length for '%s'",
>>                            bdrv_get_device_name(bs));
>> -        return;
>> +        goto error;
>>       }
>>       BackupBlockJob *job = block_job_create(&backup_job_driver, bs,
>> speed,
>>                                              cb, opaque, errp);
>>       if (!job) {
>> -        return;
>> +        goto error;
>>       }
>>       bdrv_op_block_all(target, job->common.blocker);
>> @@ -431,7 +526,15 @@ void backup_start(BlockDriverState *bs,
>> BlockDriverState *target,
>>       job->on_target_error = on_target_error;
>>       job->target = target;
>>       job->sync_mode = sync_mode;
>> +    job->sync_bitmap = sync_mode == MIRROR_SYNC_MODE_DIRTY_BITMAP ?
>> +                       sync_bitmap : NULL;
>>       job->common.len = len;
>>       job->common.co = qemu_coroutine_create(backup_run);
>>       qemu_coroutine_enter(job->common.co, job);
>> +    return;
>> +
>> + error:
>> +    if (sync_bitmap) {
>> +        bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
>> +    }
>>   }
>> diff --git a/block/mirror.c b/block/mirror.c
>> index 77bd1ed..271dbf3 100644
>> --- a/block/mirror.c
>> +++ b/block/mirror.c
>> @@ -718,6 +718,10 @@ void mirror_start(BlockDriverState *bs,
>> BlockDriverState *target,
>>       bool is_none_mode;
>>       BlockDriverState *base;
>> +    if (mode == MIRROR_SYNC_MODE_DIRTY_BITMAP) {
>> +        error_setg(errp, "Sync mode 'dirty-bitmap' not supported");
>> +        return;
>> +    }
>>       is_none_mode = mode == MIRROR_SYNC_MODE_NONE;
>>       base = mode == MIRROR_SYNC_MODE_TOP ? bs->backing_hd : NULL;
>>       mirror_start_job(bs, target, replaces,
>> diff --git a/blockdev.c b/blockdev.c
>> index 826d0c1..3f41e82 100644
>> --- a/blockdev.c
>> +++ b/blockdev.c
>> @@ -1569,6 +1569,7 @@ static void
>> drive_backup_prepare(BlkTransactionState *common, Error **errp)
>>                        backup->sync,
>>                        backup->has_mode, backup->mode,
>>                        backup->has_speed, backup->speed,
>> +                     backup->has_bitmap, backup->bitmap,
>>                        backup->has_on_source_error,
>> backup->on_source_error,
>>                        backup->has_on_target_error,
>> backup->on_target_error,
>>                        &local_err);
>> @@ -2429,6 +2430,7 @@ void qmp_drive_backup(const char *device, const
>> char *target,
>>                         enum MirrorSyncMode sync,
>>                         bool has_mode, enum NewImageMode mode,
>>                         bool has_speed, int64_t speed,
>> +                      bool has_bitmap, const char *bitmap,
>>                         bool has_on_source_error, BlockdevOnError
>> on_source_error,
>>                         bool has_on_target_error, BlockdevOnError
>> on_target_error,
>>                         Error **errp)
>> @@ -2436,6 +2438,7 @@ void qmp_drive_backup(const char *device, const
>> char *target,
>>       BlockDriverState *bs;
>>       BlockDriverState *target_bs;
>>       BlockDriverState *source = NULL;
>> +    BdrvDirtyBitmap *bmap = NULL;
>>       AioContext *aio_context;
>>       BlockDriver *drv = NULL;
>>       Error *local_err = NULL;
>> @@ -2534,7 +2537,16 @@ void qmp_drive_backup(const char *device, const
>> char *target,
>>       bdrv_set_aio_context(target_bs, aio_context);
>> -    backup_start(bs, target_bs, speed, sync, on_source_error,
>> on_target_error,
>> +    if (has_bitmap) {
>> +        bmap = bdrv_find_dirty_bitmap(bs, bitmap);
>> +        if (!bmap) {
>> +            error_setg(errp, "Bitmap '%s' could not be found", bitmap);
>> +            goto out;
>> +        }
>> +    }
>> +
>> +    backup_start(bs, target_bs, speed, sync, bmap,
>> +                 on_source_error, on_target_error,
>>                    block_job_cb, bs, &local_err);
>>       if (local_err != NULL) {
>>           bdrv_unref(target_bs);
>> @@ -2592,8 +2604,8 @@ void qmp_blockdev_backup(const char *device,
>> const char *target,
>>       bdrv_ref(target_bs);
>>       bdrv_set_aio_context(target_bs, aio_context);
>> -    backup_start(bs, target_bs, speed, sync, on_source_error,
>> on_target_error,
>> -                 block_job_cb, bs, &local_err);
>> +    backup_start(bs, target_bs, speed, sync, NULL, on_source_error,
>> +                 on_target_error, block_job_cb, bs, &local_err);
>>       if (local_err != NULL) {
>>           bdrv_unref(target_bs);
>>           error_propagate(errp, local_err);
>> diff --git a/hmp.c b/hmp.c
>> index b47f331..015499f 100644
>> --- a/hmp.c
>> +++ b/hmp.c
>> @@ -1027,7 +1027,8 @@ void hmp_drive_backup(Monitor *mon, const QDict
>> *qdict)
>>       qmp_drive_backup(device, filename, !!format, format,
>>                        full ? MIRROR_SYNC_MODE_FULL :
>> MIRROR_SYNC_MODE_TOP,
>> -                     true, mode, false, 0, false, 0, false, 0, &err);
>> +                     true, mode, false, 0, false, NULL,
>> +                     false, 0, false, 0, &err);
>>       hmp_handle_error(mon, &err);
>>   }
>> diff --git a/include/block/block.h b/include/block/block.h
>> index b2d84d6..8589e77 100644
>> --- a/include/block/block.h
>> +++ b/include/block/block.h
>> @@ -469,6 +469,7 @@ void bdrv_reset_dirty_bitmap(BlockDriverState *bs,
>> BdrvDirtyBitmap *bitmap,
>>                                int64_t cur_sector, int nr_sectors);
>>   void bdrv_dirty_iter_init(BlockDriverState *bs,
>>                             BdrvDirtyBitmap *bitmap, struct
>> HBitmapIter *hbi);
>> +void bdrv_set_dirty_iter(struct HBitmapIter *hbi, int64_t offset);
>>   int64_t bdrv_get_dirty_count(BlockDriverState *bs, BdrvDirtyBitmap
>> *bitmap);
>>   void bdrv_enable_copy_on_read(BlockDriverState *bs);
>> diff --git a/include/block/block_int.h b/include/block/block_int.h
>> index 7ad1950..2233790 100644
>> --- a/include/block/block_int.h
>> +++ b/include/block/block_int.h
>> @@ -588,6 +588,7 @@ void mirror_start(BlockDriverState *bs,
>> BlockDriverState *target,
>>    * @target: Block device to write to.
>>    * @speed: The maximum speed, in bytes per second, or 0 for unlimited.
>>    * @sync_mode: What parts of the disk image should be copied to the
>> destination.
>> + * @sync_bitmap: The dirty bitmap if sync_mode is
>> MIRROR_SYNC_MODE_DIRTY_BITMAP.
>>    * @on_source_error: The action to take upon error reading from the
>> source.
>>    * @on_target_error: The action to take upon error writing to the
>> target.
>>    * @cb: Completion function for the job.
>> @@ -598,6 +599,7 @@ void mirror_start(BlockDriverState *bs,
>> BlockDriverState *target,
>>    */
>>   void backup_start(BlockDriverState *bs, BlockDriverState *target,
>>                     int64_t speed, MirrorSyncMode sync_mode,
>> +                  BdrvDirtyBitmap *sync_bitmap,
>>                     BlockdevOnError on_source_error,
>>                     BlockdevOnError on_target_error,
>>                     BlockCompletionFunc *cb, void *opaque,
>> diff --git a/qapi/block-core.json b/qapi/block-core.json
>> index 940eff7..9c5a99c 100644
>> --- a/qapi/block-core.json
>> +++ b/qapi/block-core.json
>> @@ -508,10 +508,12 @@
>>   #
>>   # @none: only copy data written from now on
>>   #
>> +# @dirty-bitmap: only copy data described by the dirty bitmap. Since:
>> 2.3
>> +#
>>   # Since: 1.3
>>   ##
>>   { 'enum': 'MirrorSyncMode',
>> -  'data': ['top', 'full', 'none'] }
>> +  'data': ['top', 'full', 'none', 'dirty-bitmap'] }
>>   ##
>>   # @BlockJobType:
>> @@ -686,14 +688,17 @@
>>   #          probe if @mode is 'existing', else the format of the source
>>   #
>>   # @sync: what parts of the disk image should be copied to the
>> destination
>> -#        (all the disk, only the sectors allocated in the topmost
>> image, or
>> -#        only new I/O).
>> +#        (all the disk, only the sectors allocated in the topmost
>> image, from a
>> +#        dirty bitmap, or only new I/O).
>>   #
>>   # @mode: #optional whether and how QEMU should create a new image,
>> default is
>>   #        'absolute-paths'.
>>   #
>>   # @speed: #optional the maximum speed, in bytes per second
>>   #
>> +# @bitmap: #optional the name of dirty bitmap if sync is "dirty-bitmap"
>> +#          (Since 2.3)
>> +#
>>   # @on-source-error: #optional the action to take on an error on the
>> source,
>>   #                   default 'report'.  'stop' and 'enospc' can only
>> be used
>>   #                   if the block device supports io-status (see
>> BlockInfo).
>> @@ -711,7 +716,7 @@
>>   { 'type': 'DriveBackup',
>>     'data': { 'device': 'str', 'target': 'str', '*format': 'str',
>>               'sync': 'MirrorSyncMode', '*mode': 'NewImageMode',
>> -            '*speed': 'int',
>> +            '*speed': 'int', '*bitmap': 'str',
>>               '*on-source-error': 'BlockdevOnError',
>>               '*on-target-error': 'BlockdevOnError' } }
>> diff --git a/qmp-commands.hx b/qmp-commands.hx
>> index ce7782f..5aa3845 100644
>> --- a/qmp-commands.hx
>> +++ b/qmp-commands.hx
>> @@ -1048,7 +1048,7 @@ EQMP
>>       {
>>           .name       = "drive-backup",
>>           .args_type  =
>> "sync:s,device:B,target:s,speed:i?,mode:s?,format:s?,"
>> -                      "on-source-error:s?,on-target-error:s?",
>> +                      "bitmap:s?,on-source-error:s?,on-target-error:s?",
>>           .mhandler.cmd_new = qmp_marshal_input_drive_backup,
>>       },
>> @@ -1075,8 +1075,9 @@ Arguments:
>>               (json-string, optional)
>>   - "sync": what parts of the disk image should be copied to the
>> destination;
>>     possibilities include "full" for all the disk, "top" for only the
>> sectors
>> -  allocated in the topmost image, or "none" to only replicate new I/O
>> -  (MirrorSyncMode).
>> +  allocated in the topmost image, "dirty-bitmap" for only the dirty
>> sectors in
>> +  the bitmap, or "none" to only replicate new I/O (MirrorSyncMode).
>> +- "bitmap": dirty bitmap name for sync==dirty-bitmap
>>   - "mode": whether and how QEMU should create a new image
>>             (NewImageMode, optional, default 'absolute-paths')
>>   - "speed": the maximum speed, in bytes per second (json-int, optional)
>
> Looks good to me in general, now I need to find out what the successor
> bitmap is used for; but I guess I'll find that out by reviewing the rest
> of this series.
>
> Max

-- 
—js