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Re: [Qemu-devel] [PULL for-2.1 13/24] qemu-img create: add 'nocow' optio
From: |
Chun Yan Liu |
Subject: |
Re: [Qemu-devel] [PULL for-2.1 13/24] qemu-img create: add 'nocow' option |
Date: |
Tue, 01 Jul 2014 22:34:41 -0600 |
>>> On 7/2/2014 at 11:10 AM, in message <address@hidden>, Eric Blake
<address@hidden> wrote:
> 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/)
>
http://thread.gmane.org/gmane.comp.emulators.qemu/284536
-Chunyan
> --
> Eric Blake eblake redhat com +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>
- [Qemu-devel] [PULL for-2.1 03/24] dataplane: bail out on unsupported transport, (continued)
- [Qemu-devel] [PULL for-2.1 03/24] dataplane: bail out on unsupported transport, Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 06/24] virtio-blk: use aliases instead of duplicate qdev properties, Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 07/24] virtio-blk: drop virtio_blk_set_conf(), Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 08/24] virtio: fix virtio-blk child refcount in transports, Stefan Hajnoczi, 2014/07/01
- [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
- [Qemu-devel] [PULL for-2.1 14/24] iotests: Simplify qemu-iotests-quick.sh, Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 15/24] iotests: Add qemu tests to quick group, Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 17/24] block: make 'top' argument to block-commit optional, Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 16/24] iotests: Add more tests to quick group, Stefan Hajnoczi, 2014/07/01
- [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
- [Qemu-devel] [PULL for-2.1 20/24] qapi: Change back sector-count to sectors-count in quorum QAPI events., Stefan Hajnoczi, 2014/07/01
- [Qemu-devel] [PULL for-2.1 21/24] block: add QAPI command to allow live backing file change, Stefan Hajnoczi, 2014/07/01