Am 02.07.2012 12:57, schrieb Peter Crosthwaite: > On Mon, Jul 2, 2012 at 8:52 PM, Kevin Wolf <kw...@redhat.com> wrote: >> Am 02.07.2012 12:18, schrieb Peter Crosthwaite: >>> On Mon, Jul 2, 2012 at 8:01 PM, Kevin Wolf <kw...@redhat.com> wrote: >>>> Am 02.07.2012 11:42, schrieb Peter Crosthwaite: >>>>> On Mon, Jul 2, 2012 at 7:04 PM, Kevin Wolf <kw...@redhat.com> wrote: >>>>>> Am 02.07.2012 10:57, schrieb Peter Crosthwaite: >>>>>>> No conditional on the qemu_coroutine_create. So it will always create >>>>>>> a new coroutine for its work which will solve my problem. All I need >>>>>>> to do is pump events once at the end of machine model creation. Any my >>>>>>> coroutines will never yield or get queued by block/AIO. Sound like a >>>>>>> solution? >>>>>> >>>>>> If you don't need the read data in your initialisation code, >>>>> >>>>> definately not :) Just as long as the read data is there by the time >>>>> the machine goes live. Whats the current policy with bdrv_read()ing >>>>> from init functions anyway? Several devices in qemu have init >>>>> functions that read the entire storage into a buffer (then the guest >>>>> just talks to the buffer rather than the backing store). >>>> >>>> Reading from block devices during device initialisation breaks >>>> migration, so I'd like to see it go away wherever possible. Reading in >>>> the whole image file doesn't sound like something for which a good >>>> excuse exists, >>> >>> Makes sense for small devices on embedded platforms. You end up with a >>> very simple and clean device model. The approach is totally broken for >>> HDDs but it does make some sense for the little embedded flashes where >>> you can get away with caching the entire device storage in RAM for the >>> lifetime of the system. >> >> It kind of works for read-only devices, it's just ugly there. With >> writeable devices it makes the VM unmigratable. >> > > Isnt it just a simple case of syncing the buffer with the backing > store on pre_save?
Not if the buffer is only read during initialisation, which has long happened on the destination when pre_save runs. So you'd need to either migrate the whole block device content as suggested by PMM (works only for really small devices) or have a reopen in post_load. Both sounds rather hackish to me and likely doesn't work for block devices in general. Kevin
