On Mon, Nov 14, 2011 at 10:58:16AM +0100, Kevin Wolf wrote: > Am 12.11.2011 11:25, schrieb Avi Kivity: > > On 11/11/2011 12:15 PM, Kevin Wolf wrote: > >> Am 10.11.2011 22:30, schrieb Anthony Liguori: > >>> Live migration with qcow2 or any other image format is just not going to work > >>> right now even with proper clustered storage. I think doing a block level flush > >>> cache interface and letting block devices decide how to do it is the best approach. > >> > >> I would really prefer reusing the existing open/close code. It means > >> less (duplicated) code, is existing code that is well tested and doesn't > >> make migration much of a special case. > >> > >> If you want to avoid reopening the file on the OS level, we can reopen > >> only the topmost layer (i.e. the format, but not the protocol) for now > >> and in 1.1 we can use bdrv_reopen(). > > > > Intuitively I dislike _reopen style interfaces. If the second open > > yields different results from the first, does it invalidate any > > computations in between? > > Not sure what results and what computation you mean, but let me clarify > a bit about bdrv_reopen: > > The main purpose of bdrv_reopen() is to change flags, for example toggle > O_SYNC during runtime in order to allow the guest to toggle WCE. This > doesn't necessarily mean a close()/open() sequence if there are other > means to change the flags, like fcntl() (or even using other protocols > than files). > > The idea here was to extend this to invalidate all caches if some > specific flag is set. As you don't change any other flag, this will > usually not be a reopen on a lower level. > > If we need to use open() though, and it fails (this is really the only > "different" result that comes to mind) then bdrv_reopen() would fail and > the old fd would stay in use. Migration would have to fail, but I don't > think this case is ever needed for reopening after migration. > > > What's wrong with just delaying the open? > > Nothing, except that with today's code it's harder to do. > > Kevin It seems cleaner, though, doesn't it? -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
