Am 09.08.2011 11:22, schrieb supriya kannery: > Kevin Wolf wrote: >> Am 08.08.2011 09:02, schrieb Supriya Kannery: >> >>> On 08/05/2011 09:19 PM, Anthony Liguori wrote: >>> >>>> 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<h...@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. >>>> >>>> >>> We discussed the following so far... >>> 1. How to safely reopen image files >>> 2. Dynamic hostcache change >>> 3. Support for dynamic change of O_DSYNC >>> >>> Since 2 is independent of 1, shall I go ahead implementing >>> hostcache change using fcntl. >>> >>> Implementation for safely reopening image files using "BDRVReopenState" >>> can be done separately as a pre-requisite before implementing 3 >>> >> >> Doing it separately means that we would introduce yet another callback >> that is used just to change O_DIRECT. In the end we want it to use >> bdrv_reopen(), too, so I'm not sure if there is a need for a temporary >> solution. >> >> > Could you please explain "In the end we want it to use bdrv_reopen" at > bit more. > When fcntl() can change O_DIRECT on open fd , is there a need to > "re-open" > the image file? > > Considering the current way of having separate high level commands for > changing block parameters (block_set_hostcache, and may be block_set_flush > in furture), these dynamic requests will be sequential. So wouldn't it > be better to > avoid re-opening of image if possible for individual flag change request > that comes in? >> Actually, once we know what we really want (I haven't seen many comments >> on the BDRVReopenState suggestion yet), it should be pretty easy to >> implement. >> >> Kevin >> > Will work on to get an RFC patch with this proposed BDRVReopenState to > get more > inputs.
Are you still going to prepare an RFC patch implementing bdrv_reopen_prepare/commit/abort using a BDRVReopenState? Or has it even been posted and I just missed it? Kevin
