Re: [Qemu-devel] Safely reopening image files by stashing fds

[Anthony Liguori <anthony@codemonkey.ws>]

On 08/05/2011 10:43 AM, Kevin Wolf wrote:
> Am 05.08.2011 17:24, schrieb Stefan Hajnoczi:
>> On Fri, Aug 5, 2011 at 3:28 PM, Christoph Hellwig<hch@lst.de>  wrote:
>>> On Fri, Aug 05, 2011 at 02:12:48PM +0100, Daniel P. Berrange wrote:
>>>>> Because you cannot change O_DIRECT on an open fd :(.  This is why
>>>>> we're going through this pain.
>>>>
>>>> Hmm, I remember hearing that before, but looking at the current fcntl()
>>>> manpage, it claims you *can* change O_DIRECT using SET_FL. Perhaps this
>>>> is a newish feature, but it'd be nicer to use it if possible ?
>>>
>>> It's been there since day 1 of O_DIRECT support.
>>
>> Sorry, my bad.  So for Linux we could just use fcntl for
>> block_set_hostcache and not bother with reopening.  However, we will
>> need to reopen should we wish to support changing O_DSYNC.
>
> We do wish to support that.
>
> Anthony thinks that allowing the guest to toggle WCE is a prerequisite
> for making cache=writeback the default. And this is something that I
> definitely want to do for 1.0.

Indeed.

Regards,

Anthony Liguori

> Kevin
>