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Re: [Qemu-devel] [PATCH] sheepdog: implement SD_OP_FLUSH_VDI operation
From: |
MORITA Kazutaka |
Subject: |
Re: [Qemu-devel] [PATCH] sheepdog: implement SD_OP_FLUSH_VDI operation |
Date: |
Tue, 24 Apr 2012 01:26:43 +0900 |
User-agent: |
Wanderlust/2.14.0 (Africa) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (Gojō) APEL/10.8 Emacs/22.3 (x86_64-pc-linux-gnu) MULE/5.0 (SAKAKI) |
At Mon, 23 Apr 2012 08:08:46 +0200,
Christoph Hellwig wrote:
>
> On Fri, Apr 20, 2012 at 12:15:36PM -0700, MORITA Kazutaka wrote:
> > His patch sets the SD_FLAG_CMD_CACHE flag for writes only when the
> > user selects cache=writeback or cache=none. If SD_FLAG_CMD_CACHE is
> > not set in the request, Sheepdog servers are forced to flush the cache
> > like FUA commands.
>
> Ok, I missed that part and it thus seems ok. What still sems missing
> is error handling in case the sheepdog cluster doesn't actually support
> the new flag. What happens if cache=none is specified with a cluster
> not actually supporting it? Remember that cache=none is the default for
> many management frontends to qemu.
SD_FLAG_CMD_CACHE is ignored in the older version of Sheepdog, so,
even if we specify cache=writeback or cache=none, the data is written
with O_DSYNC always and cannot be cached in the server's page cache or
volatile disk cache either. I think it is safe.
It seems that there is another version problem with this patch;
bdrv_co_flush_to_disk() results in error with the older Sheepdog which
doesn't support SD_OP_FLUSH_VDI. The simple fix is to increment
SD_PROTO_VER and prevent the newer qemu from connecting to the older
Sheepdog cluster, I think.
Thanks,
Kazutaka
- [Qemu-devel] [PATCH v4 UPDATE] sheepdog: implement SD_OP_FLUSH_VDI operation, (continued)
- [Qemu-devel] [PATCH v4 UPDATE] sheepdog: implement SD_OP_FLUSH_VDI operation, Liu Yuan, 2012/04/03
- Re: [Qemu-devel] [PATCH v4 UPDATE] sheepdog: implement SD_OP_FLUSH_VDI operation, MORITA Kazutaka, 2012/04/03
- Re: [Qemu-devel] [PATCH v4 UPDATE] sheepdog: implement SD_OP_FLUSH_VDI operation, Kevin Wolf, 2012/04/03
- [Qemu-devel] [PATCH v5] sheepdog: implement SD_OP_FLUSH_VDI operation, Liu Yuan, 2012/04/03
- Re: [Qemu-devel] [PATCH v5] sheepdog: implement SD_OP_FLUSH_VDI operation, Kevin Wolf, 2012/04/04
- Re: [Qemu-devel] [PATCH v5] sheepdog: implement SD_OP_FLUSH_VDI operation, Liu Yuan, 2012/04/04
- Re: [Qemu-devel] [PATCH v5] sheepdog: implement SD_OP_FLUSH_VDI operation, Kevin Wolf, 2012/04/04
Re: [Qemu-devel] [PATCH] sheepdog: implement SD_OP_FLUSH_VDI operation, Christoph Hellwig, 2012/04/20