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Re: [Qemu-block] [Qemu-devel] block-commit & dropping privs
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-block] [Qemu-devel] block-commit & dropping privs |
Date: |
Mon, 30 Mar 2015 17:36:34 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Am 27.03.2015 um 18:12 hat Eric Blake geschrieben:
> On 03/27/2015 09:36 AM, Michael Tokarev wrote:
> > Wonder how to specify cache mode, or should I open these with proper
> > O_DIRECT/O_SYNC/whatever? It looks like it's possible to change O_DIRECT
> > at runtime but not O_SYNC.
> >
> > And the more interesting question is how to do that from shell.
>
> Redirections only get you so far in shell; you may need a wrapper C
> program go get O_DIRECT and/or O_SYNC pre-set. Then again, if you use
> QMP and pass over the Unix socket, you need a C program anyways.
O_DIRECT can be set with fcntl(), so qemu takes care of that. O_SYNC
is completely unused on Linux these days, so that shouldn't be a problem
either. (Other platforms use it as a misguided attempt of approximating
O_DIRECT. We should really error out instead.)
So if I'm not mistaken, just having one read-only and one read-write fd
should be enough for any configuration in practice.
Kevin
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