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From: | Paolo Bonzini |
Subject: | Re: [Qemu-devel] [PATCH 0/2] block: Write out internal caches even with cache=unsafe |
Date: | Mon, 24 Oct 2011 09:53:07 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:7.0) Gecko/20110927 Thunderbird/7.0 |
On 10/24/2011 09:37 AM, Kevin Wolf wrote:
Why? cache=unsafe is explicitly allowing to s/data/manure/ on crash.It's surely expected on a host crash, but is it for a qemu crash? cache=unsafe was introduced to avoid fsync() costs, which it still does after this patch.
I think it's not about "why is it there", but rather about "what is it useful for". My interpretation of it is "I do not need the image anymore unless the command exits cleanly": VM installations, qemu-img conversions, BDRV_O_SNAPSHOT (doesn't do it yet, but it could). Even SIGINT and SIGTERM would be excluded from this definition, but they cost nothing so it's nice to include them.
If you do this for raw-posix, you need to do it for all protocols.rbd could use it, too, right. Any other protocol I missed?
NBD could, but it doesn't support flush yet.In general, even if it were useful to implement this, I'm not sure this is the best way to implement it. For example you could simply clear BDRV_O_NO_FLUSH in qcow2_open.
Paolo
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