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From: Jeff Cody <jcody@redhat.com>
To: Fam Zheng <famz@redhat.com>
Cc: kwolf@redhat.com, benoit.canet@irqsave.net, rjones@redhat.com,
	qemu-devel@nongnu.org, armbru@redhat.com, imain@redhat.com,
	stefanha@redhat.com, pbonzini@redhat.com
Subject: Re: [Qemu-devel] [PATCH v14 09/14] stream: Use bdrv_drop_intermediate and drop close_unused_images
Date: Wed, 19 Feb 2014 16:23:05 -0500	[thread overview]
Message-ID: <20140219212305.GB9677@localhost.localdomain> (raw)
In-Reply-To: <1392817351-22148-10-git-send-email-famz@redhat.com>

On Wed, Feb 19, 2014 at 09:42:26PM +0800, Fam Zheng wrote:
> This reuses the new bdrv_drop_intermediate.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  block/stream.c | 30 +-----------------------------
>  1 file changed, 1 insertion(+), 29 deletions(-)
> 
> diff --git a/block/stream.c b/block/stream.c
> index dd0b4ac..9cdcf0e 100644
> --- a/block/stream.c
> +++ b/block/stream.c
> @@ -51,34 +51,6 @@ static int coroutine_fn stream_populate(BlockDriverState *bs,
>      return bdrv_co_copy_on_readv(bs, sector_num, nb_sectors, &qiov);
>  }
>  
> -static void close_unused_images(BlockDriverState *top, BlockDriverState *base,
> -                                const char *base_id)
> -{
> -    BlockDriverState *intermediate;
> -    intermediate = top->backing_hd;
> -
> -    /* Must assign before bdrv_delete() to prevent traversing dangling pointer
> -     * while we delete backing image instances.
> -     */
> -    top->backing_hd = base;
> -
> -    while (intermediate) {
> -        BlockDriverState *unused;
> -
> -        /* reached base */
> -        if (intermediate == base) {
> -            break;
> -        }
> -
> -        unused = intermediate;
> -        intermediate = intermediate->backing_hd;
> -        unused->backing_hd = NULL;
> -        bdrv_unref(unused);
> -    }
> -
> -    bdrv_refresh_limits(top);
> -}
> -
>  static void coroutine_fn stream_run(void *opaque)
>  {
>      StreamBlockJob *s = opaque;
> @@ -192,7 +164,7 @@ wait:
>              }
>          }


>          ret = bdrv_change_backing_file(bs, base_id, base_fmt);

This is redundant if bdrv_drop_intermediate() is used, and can be
removed.

> -        close_unused_images(bs, base, base_id);
> +        bdrv_drop_intermediate(bs, bs->backing_hd, base);

Previously, if base == NULL and base_id == NULL, that meant that we
were streaming from the very first backing file all the way up to the
active layer.  When close_unused_images() was called with base ==
NULL, the BDS chain was flattened and the active layer became all that
was left.

By calling bdrv_drop_intermediate() with base == NULL, we get the same
behavior, so that is OK.

What about if base != NULL here?  It still works OK, but now 'base' is
really 'bs->backing_hd'.  But I don't think we care anymore in this
function, or in the streaming block job, so I think it is OK.



>      }
>  
>      qemu_vfree(buf);
> -- 
> 1.8.5.4
> 
> 

  reply	other threads:[~2014-02-19 21:25 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-02-19 13:42 [Qemu-devel] [PATCH v14 00/14] Drop in_use from BlockDriverState and enable point-in-time snapshot exporting over NBD Fam Zheng
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 01/14] block: Add BlockOpType enum Fam Zheng
2014-02-19 15:25   ` Benoît Canet
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 02/14] block: Introduce op_blockers to BlockDriverState Fam Zheng
2014-02-19 15:26   ` Benoît Canet
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 03/14] block: Replace in_use with operation blocker Fam Zheng
2014-02-19 15:26   ` Benoît Canet
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 04/14] block: Move op_blocker check from block_job_create to its caller Fam Zheng
2014-02-19 15:28   ` Benoît Canet
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 05/14] block: Add bdrv_set_backing_hd() Fam Zheng
2014-02-19 15:27   ` Benoît Canet
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 06/14] block: Add backing_blocker in BlockDriverState Fam Zheng
2014-02-19 15:32   ` Benoît Canet
2014-02-19 21:17   ` Jeff Cody
2014-02-20  5:01     ` Fam Zheng
2014-02-20  5:08       ` Jeff Cody
2014-02-20  8:28         ` Fam Zheng
2014-02-20 11:59           ` Jeff Cody
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 07/14] block: Parse "backing" option to reference existing BDS Fam Zheng
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 08/14] block: Support dropping active in bdrv_drop_intermediate Fam Zheng
2014-02-19 15:34   ` Benoît Canet
2014-02-19 21:22   ` Jeff Cody
2014-02-19 23:24     ` Jeff Cody
2014-02-20  4:37       ` Fam Zheng
2014-02-20  5:57         ` Jeff Cody
2014-02-20  8:34           ` Fam Zheng
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 09/14] stream: Use bdrv_drop_intermediate and drop close_unused_images Fam Zheng
2014-02-19 21:23   ` Jeff Cody [this message]
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 10/14] qmp: Add command 'blockdev-backup' Fam Zheng
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 11/14] block: Allow backup on referenced named BlockDriverState Fam Zheng
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 12/14] block: Add blockdev-backup to transaction Fam Zheng
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 13/14] qemu-iotests: Test blockdev-backup in 055 Fam Zheng
2014-02-19 13:42 ` [Qemu-devel] [PATCH v14 14/14] qemu-iotests: Image fleecing test case 081 Fam Zheng

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