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Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command |
Date: |
Tue, 21 May 2013 09:31:59 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, May 20, 2013 at 09:23:43AM +0200, Paolo Bonzini wrote:
> Il 20/05/2013 08:24, Stefan Hajnoczi ha scritto:
> >> > You only need to fdatasync() before every guest flush, no?
> > No, you need to set the dirty bit before issuing the write on the
> > host. Otherwise the image data may be modified without setting the
> > appropriate dirty bit. That would allow data modifications to go
> > undetected!
>
> But data modifications can go undetected until the guest flush returns,
> can't they?
You are thinking about it from the guest perspective - if a flush has
not completed yet then there is no guarantee that the write has reached
disk.
But from a host perspective the dirty bitmap should be conservative so
that the backup application can always restore a bit-for-bit identical
copy of the disk image. It would be weird if writes can sneak in
unnoticed.
Stefan
- Re: [Qemu-devel] [PATCH v3 7/8] blockdev: add Abort transaction, (continued)
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Paolo Bonzini, 2013/05/17
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Stefan Hajnoczi, 2013/05/20
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Paolo Bonzini, 2013/05/20
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command,
Stefan Hajnoczi <=
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Paolo Bonzini, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Stefan Hajnoczi, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Paolo Bonzini, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Dietmar Maurer, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Stefan Hajnoczi, 2013/05/22
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Dietmar Maurer, 2013/05/22
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Dietmar Maurer, 2013/05/22
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Stefan Hajnoczi, 2013/05/23
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Dietmar Maurer, 2013/05/23
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Stefan Hajnoczi, 2013/05/24