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Re: [Qemu-devel] [PULL for-2.1 13/24] qemu-img create: add 'nocow' optio
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PULL for-2.1 13/24] qemu-img create: add 'nocow' option |
Date: |
Tue, 01 Jul 2014 21:10:56 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 |
On 07/01/2014 02:48 AM, Stefan Hajnoczi wrote:
> From: Chunyan Liu <address@hidden>
>
> Add 'nocow' option so that users could have a chance to set NOCOW flag to
> newly created files. It's useful on btrfs file system to enhance performance.
>
> Btrfs has low performance when hosting VM images, even more when the guest
> in those VM are also using btrfs as file system. One way to mitigate this bad
> performance is to turn off COW attributes on VM files. Generally, there are
> two ways to turn off NOCOW on btrfs: a) by mounting fs with nodatacow, then
> all newly created files will be NOCOW. b) per file. Add the NOCOW file
> attribute. It could only be done to empty or new files.
>
> This patch tries the second way, according to the option, it could add NOCOW
> per file.
>
> For most block drivers, since the create file step is in raw-posix.c, so we
> can do setting NOCOW flag ioctl in raw-posix.c only.
>
> But there are some exceptions, like block/vpc.c and block/vdi.c, they are
> creating file by calling qemu_open directly. For them, do the same setting
> NOCOW flag ioctl work in them separately.
>
> [Fixed up 082.out due to the new 'nocow' creation option
> --Stefan]
>
> Signed-off-by: Chunyan Liu <address@hidden>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
I see this is already in qemu.git, so it will need a followup to fix the
user-visible typos (s/trun/turn/, s/Capitabl/Capital/)
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- [Qemu-devel] [PULL for-2.1 05/24] qdev: add qdev_alias_all_properties(), (continued)
- [Qemu-devel] [PULL for-2.1 05/24] qdev: add qdev_alias_all_properties(), Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 03/24] dataplane: bail out on unsupported transport, Stefan Hajnoczi, 2014/07/01
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- [Qemu-devel] [PULL for-2.1 07/24] virtio-blk: drop virtio_blk_set_conf(), Stefan Hajnoczi, 2014/07/01
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- [Qemu-devel] [PULL for-2.1 09/24] virtio-blk: move qdev properties into virtio-blk.c, Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 10/24] virtio-blk: replace x-iothread with iothread link property, Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 11/24] qdev: drop iothread property type, Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 12/24] virtio-blk: remove need for explicit x-data-plane=on option, Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 13/24] qemu-img create: add 'nocow' option, Stefan Hajnoczi, 2014/07/01
- Re: [Qemu-devel] [PULL for-2.1 13/24] qemu-img create: add 'nocow' option,
Eric Blake <=
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- [Qemu-devel] [PULL for-2.1 15/24] iotests: Add qemu tests to quick group, Stefan Hajnoczi, 2014/07/01
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- [Qemu-devel] [PULL for-2.1 18/24] block: simplify bdrv_find_base() and bdrv_find_overlay(), Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 19/24] block/cow: Avoid use of uninitialized cow_bs in error path, Stefan Hajnoczi, 2014/07/01
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