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[Qemu-devel] bdrv_flush for qemu block drivers nbd, rbd and sheepdog
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] bdrv_flush for qemu block drivers nbd, rbd and sheepdog |
Date: |
Thu, 21 Oct 2010 16:07:28 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.12) Gecko/20100907 Fedora/3.0.7-1.fc12 Thunderbird/3.0.7 |
Hi all,
I'm currently looking into adding a return value to qemu's bdrv_flush
function and I noticed that your block drivers (nbd, rbd and sheepdog)
don't implement bdrv_flush at all. bdrv_flush is going to return
-ENOTSUP for any block driver not implementing this, effectively
breaking these three drivers for anything but cache=unsafe.
Is there a specific reason why your drivers don't implement this? I
think I remember that one of the drivers always provides
cache=writethough semantics. It would be okay to silently "upgrade" to
cache=writethrough, so in this case I'd just need to add an empty
bdrv_flush implementation.
Otherwise, we really cannot allow any option except cache=unsafe because
that's the semantics provided by the driver.
In any case, I think it would be a good idea to implement a real
bdrv_flush function to allow the write-back cache modes cache=off and
cache=writeback in order to improve performance over writethrough.
Is this possible with your protocols, or can the protocol be changed to
consider this? Any hints on how to proceed?
Kevin
- [Qemu-devel] bdrv_flush for qemu block drivers nbd, rbd and sheepdog,
Kevin Wolf <=
- Re: [Qemu-devel] bdrv_flush for qemu block drivers nbd, rbd and sheepdog, Anthony Liguori, 2010/10/21
- Re: [Qemu-devel] bdrv_flush for qemu block drivers nbd, rbd and sheepdog, Laurent Vivier, 2010/10/21
- Re: [Qemu-devel] bdrv_flush for qemu block drivers nbd, rbd and sheepdog, Kevin Wolf, 2010/10/22
- Re: [Qemu-devel] bdrv_flush for qemu block drivers nbd, rbd and sheepdog, Anthony Liguori, 2010/10/22
- Re: [Qemu-devel] bdrv_flush for qemu block drivers nbd, rbd and sheepdog, Kevin Wolf, 2010/10/22
- Re: [Qemu-devel] bdrv_flush for qemu block drivers nbd, rbd and sheepdog, Anthony Liguori, 2010/10/22
- Re: [Qemu-devel] bdrv_flush for qemu block drivers nbd, rbd and sheepdog, Kevin Wolf, 2010/10/22
- Re: [Qemu-devel] bdrv_flush for qemu block drivers nbd, rbd and sheepdog, Anthony Liguori, 2010/10/22
Re: [Qemu-devel] bdrv_flush for qemu block drivers nbd, rbd and sheepdog, MORITA Kazutaka, 2010/10/22