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Re: [Qemu-devel] [PATCH v2 10/11] blockdev: Block device IO during block
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v2 10/11] blockdev: Block device IO during blockdev-backup transaction |
Date: |
Wed, 13 May 2015 14:21:12 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 |
On 13/05/2015 19:28, Fam Zheng wrote:
> + state->bs = bs;
> + error_setg(&state->blocker, "blockdev-backup in progress");
> + bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, state->blocker);
> +
> qmp_blockdev_backup(backup->device, backup->target,
> backup->sync,
> backup->has_speed, backup->speed,
> @@ -1696,7 +1701,6 @@ static void blockdev_backup_prepare(BlkTransactionState
> *common, Error **errp)
> return;
> }
>
> - state->bs = bs;
I don't understand this. Jobs could pause/resume themselves by adding a
DEVICE_IO notifier on the targets.
However, block backups is the one job that cannot do this, because I/O
on the source triggers I/O on the target.
So if we consider this idea worthwhile, and decide that pausing device
I/O on the target should pause the block job, the backup job actually
has to prevent *adding a DEVICE_IO blocker* on the target. This
"meta-block" is not possible in your design, which is a pity because on
the surface it looked nicer than mine.
FWIW, my original idea was:
- bdrv_pause checks if there is an operation blocker for PAUSE. if it
is there, it fails
- otherwise, bdrv_pause invokes a notifier list if this is the outermost
call. if not the outermost call, it does nothing
- bdrv_resume does the same, but does not need a blocker
- drive-backup should block PAUSE on its target
Also, should the blockers (either DEVICE_IO in your design, or PAUSE in
mine) be included in bdrv_op_block_all. I would say no in your case;
here is the proof:
- block-backup doesn't like DEVICE_IO blockers on the target
- block-backup calls bdrv_op_block_all on the target
- hence, bdrv_op_block_all shouldn't block DEVICE_IO
block_job_create is another suspicious caller of bdrv_op_block_all. It
probably shouldn't block neither PAUSE nor DEVICE_IO.
Paolo
- Re: [Qemu-devel] [PATCH v2 05/11] virtio-blk: Don't handle output when there is "device IO" op blocker, (continued)
- [Qemu-devel] [PATCH v2 06/11] nbd-server: Clear "can_read" when "device io" blocker is set, Fam Zheng, 2015/05/13
- [Qemu-devel] [PATCH v2 07/11] blockdev: Block device IO during internal snapshot transaction, Fam Zheng, 2015/05/13
- [Qemu-devel] [PATCH v2 09/11] blockdev: Block device IO during drive-backup transaction, Fam Zheng, 2015/05/13
- [Qemu-devel] [PATCH v2 08/11] blockdev: Block device IO during external snapshot transaction, Fam Zheng, 2015/05/13
- [Qemu-devel] [PATCH v2 10/11] blockdev: Block device IO during blockdev-backup transaction, Fam Zheng, 2015/05/13
- Re: [Qemu-devel] [PATCH v2 10/11] blockdev: Block device IO during blockdev-backup transaction,
Paolo Bonzini <=
[Qemu-devel] [PATCH v2 11/11] block: Block "device IO" during bdrv_drain and bdrv_drain_all, Fam Zheng, 2015/05/13
- Re: [Qemu-devel] [PATCH v2 11/11] block: Block "device IO" during bdrv_drain and bdrv_drain_all, Paolo Bonzini, 2015/05/13
- Re: [Qemu-devel] [PATCH v2 11/11] block: Block "device IO" during bdrv_drain and bdrv_drain_all, Fam Zheng, 2015/05/13
- Re: [Qemu-devel] [PATCH v2 11/11] block: Block "device IO" during bdrv_drain and bdrv_drain_all, Paolo Bonzini, 2015/05/13
- Re: [Qemu-devel] [PATCH v2 11/11] block: Block "device IO" during bdrv_drain and bdrv_drain_all, Fam Zheng, 2015/05/13
- Re: [Qemu-devel] [PATCH v2 11/11] block: Block "device IO" during bdrv_drain and bdrv_drain_all, Paolo Bonzini, 2015/05/13
- Re: [Qemu-devel] [PATCH v2 11/11] block: Block "device IO" during bdrv_drain and bdrv_drain_all, Fam Zheng, 2015/05/13