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Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver |
Date: |
Tue, 21 May 2013 18:03:01 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6 |
Il 21/05/2013 17:54, Dietmar Maurer ha scritto:
>>>> Hmm, right. But do we need the bitmap at all? We can just use
>>>>> bdrv_is_allocated like bdrv_co_do_readv does.
>>> If a write occur, we read and backup that cluster immediately (out of
>>> order). So I am quite sure we need the bitmap.
>>
>> This is the same as how copy-on-read happens during image streaming, and it
>> doesn't use a bitmap.
>
> But a read does not modify the content.
Copy-on-read modifies the topmost image even without changing the
content, just like copy-before-write modifies the backup image.
But writes to the backup copy are serialized anyway via
wait_for_overlapping_requests, so there is no problem here.
Paolo
- Re: [Qemu-devel] [PATCH v3 3/8] block: add drive-backup QMP command, (continued)
- [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver, Stefan Hajnoczi, 2013/05/15
- Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver, Wenchao Xia, 2013/05/15
- Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver, Paolo Bonzini, 2013/05/20
- Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver, Stefan Hajnoczi, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver, Paolo Bonzini, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver, Dietmar Maurer, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver, Paolo Bonzini, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver, Dietmar Maurer, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver, Dietmar Maurer, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver, Dietmar Maurer, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver, Paolo Bonzini, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 2/8] block: add basic backup support to block driver, Stefan Hajnoczi, 2013/05/22
[Qemu-devel] [PATCH v3 7/8] blockdev: add Abort transaction, Stefan Hajnoczi, 2013/05/15
Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Wenchao Xia, 2013/05/16