Re: [Qemu-devel] [PATCH v12 08/17] qmp: add block-dirty-bitmap-clear

[John Snow <jsnow@redhat.com>]

On 02/11/2015 01:28 PM, Max Reitz wrote:
> On 2015-02-09 at 20:35, John Snow wrote:
>> Add bdrv_clear_dirty_bitmap and a matching QMP command,
>> qmp_block_dirty_bitmap_clear that enables a user to reset
>> the bitmap attached to a drive.
>>
>> This allows us to reset a bitmap in the event of a full
>> drive backup.
>>
>> Signed-off-by: John Snow <jsnow@redhat.com>
>> ---
>>   block.c               |  7 +++++++
>>   blockdev.c            | 31 +++++++++++++++++++++++++++++++
>>   include/block/block.h |  1 +
>>   qapi/block-core.json  | 14 ++++++++++++++
>>   qmp-commands.hx       | 24 ++++++++++++++++++++++++
>>   5 files changed, 77 insertions(+)
>>
>> diff --git a/block.c b/block.c
>> index e93fceb..ad33d96 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -62,6 +62,7 @@
>>   struct BdrvDirtyBitmap {
>>       HBitmap *bitmap;
>>       BdrvDirtyBitmap *successor;
>> +    int64_t size;
>>       char *name;
>>       bool disabled;
>>       QLIST_ENTRY(BdrvDirtyBitmap) list;
>> @@ -5422,6 +5423,7 @@ BdrvDirtyBitmap
>> *bdrv_create_dirty_bitmap(BlockDriverState *bs,
>>       }
>>       bitmap = g_new0(BdrvDirtyBitmap, 1);
>>       bitmap->bitmap = hbitmap_alloc(bitmap_size,
>> ffs(sector_granularity) - 1);
>> +    bitmap->size = bitmap_size;
>>       bitmap->name = g_strdup(name);
>>       bitmap->disabled = false;
>>       QLIST_INSERT_HEAD(&bs->dirty_bitmaps, bitmap, list);
>> @@ -5624,6 +5626,11 @@ void bdrv_reset_dirty_bitmap(BlockDriverState
>> *bs, BdrvDirtyBitmap *bitmap,
>>       hbitmap_reset(bitmap->bitmap, cur_sector, nr_sectors);
>>   }
>> +void bdrv_clear_dirty_bitmap(BdrvDirtyBitmap *bitmap)
>> +{
>> +    hbitmap_reset(bitmap->bitmap, 0, bitmap->size);
>> +}
>
> Is it fine to use this function on frozen or disabled bitmaps? The QMP
> interface at least suggests the former isn't, but I think the latter
> shouldn't be either (which may be wrong, though).
>

Bug. This should be prohibited for frozen or disabled bitmaps, yes.

>> +
>>   static void bdrv_set_dirty(BlockDriverState *bs, int64_t cur_sector,
>>                              int nr_sectors)
>>   {
>> diff --git a/blockdev.c b/blockdev.c
>> index 3f41e82..83d0608 100644
>> --- a/blockdev.c
>> +++ b/blockdev.c
>> @@ -2116,6 +2116,37 @@ void qmp_block_dirty_bitmap_disable(const char
>> *node, const char *name,
>>       aio_context_release(aio_context);
>>   }
>> +/**
>> + * Completely clear a bitmap, for the purposes of synchronizing a bitmap
>> + * immediately after a full backup operation.
>> + */
>> +void qmp_block_dirty_bitmap_clear(const char *node, const char *name,
>> +                                  Error **errp)
>> +{
>> +    AioContext *aio_context;
>> +    BdrvDirtyBitmap *bitmap;
>> +    BlockDriverState *bs;
>> +
>> +    bitmap = block_dirty_bitmap_lookup(node, name, &bs, errp);
>> +    if (!bitmap) {
>> +        return;
>> +    }
>> +
>> +    aio_context = bdrv_get_aio_context(bs);
>> +    aio_context_acquire(aio_context);
>> +
>> +    if (bdrv_dirty_bitmap_frozen(bitmap)) {
>> +        error_setg(errp,
>> +                   "Bitmap '%s' is currently frozen and cannot be
>> modified.\n",
>> +                   name);
>> +        goto out;
>> +    }
>> +    bdrv_clear_dirty_bitmap(bitmap);
>> +
>> + out:
>> +    aio_context_release(aio_context);
>> +}
>> +
>>   int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
>>   {
>>       const char *id = qdict_get_str(qdict, "id");
>> diff --git a/include/block/block.h b/include/block/block.h
>> index 8589e77..8916ecd 100644
>> --- a/include/block/block.h
>> +++ b/include/block/block.h
>> @@ -467,6 +467,7 @@ void bdrv_set_dirty_bitmap(BlockDriverState *bs,
>> BdrvDirtyBitmap *bitmap,
>>                              int64_t cur_sector, int nr_sectors);
>>   void bdrv_reset_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap
>> *bitmap,
>>                                int64_t cur_sector, int nr_sectors);
>> +void bdrv_clear_dirty_bitmap(BdrvDirtyBitmap *bitmap);
>>   void bdrv_dirty_iter_init(BlockDriverState *bs,
>>                             BdrvDirtyBitmap *bitmap, struct
>> HBitmapIter *hbi);
>>   void bdrv_set_dirty_iter(struct HBitmapIter *hbi, int64_t offset);
>> diff --git a/qapi/block-core.json b/qapi/block-core.json
>> index 9c5a99c..702b76a 100644
>> --- a/qapi/block-core.json
>> +++ b/qapi/block-core.json
>> @@ -1050,6 +1050,20 @@
>>     'data': 'BlockDirtyBitmap' }
>>   ##
>> +# @block-dirty-bitmap-clear
>> +#
>> +# Clear (reset) a dirty bitmap on the device
>> +#
>> +# Returns: nothing on success
>> +#          If @node is not a valid block device, DeviceNotFound
>> +#          If @name is not found, GenericError with an explanation
>> +#
>> +# Since 2.3
>> +##
>> +{ 'command': 'block-dirty-bitmap-clear',
>> +  'data': 'BlockDirtyBitmap' }
>> +
>> +##
>>   # @block_set_io_throttle:
>>   #
>>   # Change I/O throttle limits for a block drive.
>> diff --git a/qmp-commands.hx b/qmp-commands.hx
>> index 5aa3845..e1d96cd 100644
>> --- a/qmp-commands.hx
>> +++ b/qmp-commands.hx
>> @@ -1264,6 +1264,11 @@ EQMP
>>           .args_type  = "node:B,name:s",
>>           .mhandler.cmd_new =
>> qmp_marshal_input_block_dirty_bitmap_disable,
>>       },
>> +    {
>> +        .name       = "block-dirty-bitmap-clear",
>> +        .args_type  = "node:B,name:s",
>> +        .mhandler.cmd_new = qmp_marshal_input_block_dirty_bitmap_clear,
>> +    },
>>   SQMP
>> @@ -1303,6 +1308,25 @@ Example:
>>                                                         "name":
>> "bitmap0" } }
>>   <- { "return": {} }
>> +block-dirty-bitmap-clear
>> +-------------------------
>
> One dash too many (critical!).
>
> Max
>

Yes.

>> +Since 2.3
>> +
>> +Reset the dirty bitmap associated with a node so that an incremental
>> backup
>> +from this point in time forward will only backup clusters modified
>> after this
>> +clear operation.
>> +
>> +Arguments:
>> +
>> +- "node": device/node on which to remove dirty bitmap (json-string)
>> +- "name": name of the dirty bitmap to remove (json-string)
>> +
>> +Example:
>> +
>> +-> { "execute": "block-dirty-bitmap-clear", "arguments": { "node":
>> "drive0",
>> +                                                           "name":
>> "bitmap0" } }
>> +<- { "return": {} }
>> +
>>   EQMP
>>       {
>
>