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Re: [Qemu-block] [PATCH v2 01/11] block: Add op blocker type "device IO"
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From: |
Paolo Bonzini |
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Subject: |
Re: [Qemu-block] [PATCH v2 01/11] block: Add op blocker type "device IO" |
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Date: |
Wed, 13 May 2015 17:09:52 +0200 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 |
On 13/05/2015 17:02, Fam Zheng wrote:
>> > For example, SCSI requests can result in many consecutive I/Os:
>> >
>> > (1) FUA requests are split in write+flush
>> >
>> > (2) adapters that do not use QEMUSGList-based I/O only read 128K at a time
>> >
>> > (3) WRITE SAME operations are also split in chunks
>> >
>> > (4) UNMAP operations process one descriptor at a time
> I don't understand the point of these examples. If we don't return -EBUSY
> here,
> the request will sneak into block/io.c and perhaps break qmp transaction
> semantics, if it lands between two backups.
It won't, because after blocking DEVICE_IO you will always drain I/O and
the bdrv_drain will loop until the above are all satisfied.
Paolo
[Qemu-block] [PATCH v2 03/11] block-backend: Add blk_op_blocker_add_notifier, Fam Zheng, 2015/05/13
[Qemu-block] [PATCH v2 02/11] block: Add op blocker notifier list, Fam Zheng, 2015/05/13
[Qemu-block] [PATCH v2 04/11] virtio-blk: Move complete_request to 'ops' structure, Fam Zheng, 2015/05/13
[Qemu-block] [PATCH v2 05/11] virtio-blk: Don't handle output when there is "device IO" op blocker, Fam Zheng, 2015/05/13
[Qemu-block] [PATCH v2 07/11] blockdev: Block device IO during internal snapshot transaction, Fam Zheng, 2015/05/13
[Qemu-block] [PATCH v2 06/11] nbd-server: Clear "can_read" when "device io" blocker is set, Fam Zheng, 2015/05/13
[Qemu-block] [PATCH v2 08/11] blockdev: Block device IO during external snapshot transaction, Fam Zheng, 2015/05/13