Am 06.05.2019 um 11:50 hat Stefano Garzarella geschrieben: > On Fri, May 03, 2019 at 01:21:23PM -0400, Jason Dillaman wrote: > > On Fri, May 3, 2019 at 12:30 PM Stefano Garzarella <sgarz...@redhat.com> > > wrote: > > > > > > RBD APIs don't allow us to write more than the size set with > > > rbd_create() or rbd_resize(). > > > In order to support growing images (eg. qcow2), we resize the > > > image before write operations that exceed the current size. > > > > > > Signed-off-by: Stefano Garzarella <sgarz...@redhat.com> > > > --- > > > v2: > > > - use bs->total_sectors instead of adding a new field [Kevin] > > > - resize the image only during write operation [Kevin] > > > for read operation, the bdrv_aligned_preadv() already handles reads > > > that exceed the length returned by bdrv_getlength(), so IMHO we can > > > avoid to handle it in the rbd driver > > > --- > > > block/rbd.c | 14 +++++++++++++- > > > 1 file changed, 13 insertions(+), 1 deletion(-) > > > > > > diff --git a/block/rbd.c b/block/rbd.c > > > index 0c549c9935..613e8f4982 100644 > > > --- a/block/rbd.c > > > +++ b/block/rbd.c > > > @@ -934,13 +934,25 @@ static BlockAIOCB *rbd_start_aio(BlockDriverState > > > *bs, > > > } > > > > > > switch (cmd) { > > > - case RBD_AIO_WRITE: > > > + case RBD_AIO_WRITE: { > > > + /* > > > + * RBD APIs don't allow us to write more than actual size, so in > > > order > > > + * to support growing images, we resize the image before write > > > + * operations that exceed the current size. > > > + */ > > > + if (off + size > bs->total_sectors * BDRV_SECTOR_SIZE) { > > > > When will "bs->total_sectors" be refreshed to represent the correct > > current size? You wouldn't want a future write whose extent was > > greater than the original image size but less then a previous IO that > > expanded the image to attempt to shrink the image. > > > > Good point! > IIUC it can happen, because in the bdrv_aligned_pwritev() we do these > steps: > 1. call bdrv_driver_pwritev() that invokes "drv->bdrv_aio_pwritev" and > then it waits calling "qemu_coroutine_yield()" > 2. call bdrv_co_write_req_finish() that updates the "bs->total_sectors" > > Between steps 1 and 2, maybe another request can be executed, then the > issue that you described can occur. > > The solutions that I have in mind are: > a. Add a variable in the BDRVRBDState to track the latest resize.
This would work and be relatively simple. > b. Call rbd_get_size() before the rbd_resize() to be sure to avoid to shrink > the image. I'm not sure if rbd_get_size() involves network traffic or other significant complexity. If so, I'd definitely avoid it. > c. Updates the "bs->total_sectors" after the rbd_resize(), but I'm not > sure it is allowed. > > @Jason, @Kevin Do you have any advice? We need to make sure to run everything that bdrv_co_write_req_finish() does for resizing an image: bs->total_sectors = end_sector; bdrv_parent_cb_resize(bs); bdrv_dirty_bitmap_truncate(bs, end_sector << BDRV_SECTOR_BITS); Just duplicating that code wouldn't be good; if something is added, we'd probably forget updating rbd, too. So I think your solution c would at least involve refactoring the above code into a separate function that can be called from rbd. But solution a might actually be the simplest. In this case, sorry for giving you bad advice in v1 of the patch. Kevin