Am 08.12.2014 um 14:50 hat Jun Li geschrieben:
> On Mon, 12/08 11:07, Kevin Wolf wrote:
> > Am 05.12.2014 um 16:32 hat Jun Li geschrieben:
> > > Currently, qemu-img can not create qcow2 image format on rbd server.
> > > Analysis
> > > the code as followings:
> > > when create qcow2 format image:
> > > qcow2_create2
> > > bdrv_create_file(filename, opts, &local_err); --> Here will create a 0
> > > size
> > > file(e.g: file1) on rbd server.
> > > ...
> > > ret = bdrv_pwrite(bs, 0, header, cluster_size); --> So here can not
> > > write
> > > qcow2 header into file1 due to the file1's length is 0. Seems
> > > qemu_rbd_aio_writev can not write beyond EOF.
> > > ...
> > >
> > > As above analysis, there are two methods to solve the above bz as
> > > followings:
> > > 1, When create file1, just create a fixed-size file1 on rbd server(not 0
> > > size).
> >
> > This is not a solution. Even if you might be able to create an image
> > successfully, using qcow2 without a backend that allows the image file
> > to grow is bound to fail sooner or later.
> >
> > So yes, you'll want to extend the rbd block driver to grow the file
> > asynchronously when writing beyond EOF.
> >
>
> Hi Kevin,
>
> Although rbd_resize is synchronous, I just want to create a new child-thread
> to realize asynchronous(Maybe just like userspace aio: libaio) rbd_resize.
> Just like following:
>
> qemu_rbd_aio_writev()
> {
> if (BlockDriverState->file->growable == 1) {
> pthread_create(&thread_id, NULL, child_thread, NULL);
> }
>
> rbd_start_aio();
> }
>
> child_thread()
> {
> ...
> rbd_resize();
> rbd_start_aio();
> ...
> }
>
> Currently, seems do not have original asynchronous rbd_resize. Besides, rbd
> block
> driver do not support growable file. So I want to use above method to realize
> asynchronous rbd_resize() in our qemu level.
>
> What's your opinion?
Are you sure that the rbd libraries are thread-safe and can be used in
this way?
Kevin
