On Tue, 07/19 17:45, Paolo Bonzini wrote:
>
>
> On 19/07/2016 17:28, Eric Blake wrote:
> >> If I'm reading the NBD proto.md correctly, this is not enough if
> >> NBD_CMD_FLAG_NO_HOLE is specified. We probably need to use a zeroed buffer
> >> with
> >> blk_pwrite, or pass a new flag (BDRV_RED_NO_HOLE) to blk_pwrite_zeroes to
> >> enforce the bdrv_driver_pwritev() branch in bdrv_co_do_pwrite_zeroes().
>
> I agree with Eric's interpretation. It's a bit weird to have the
> direction inverted, but I'm not sure I see the ambiguity. Can you explain?
Write zeroes _means_ "punch hole" on a raw file.
In block/raw-posix.c:handle_aiocb_write_zeroes():
> #ifdef CONFIG_FALLOCATE_PUNCH_HOLE
> if (s->has_discard && s->has_fallocate) {
> int ret = do_fallocate(s->fd,
> FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> aiocb->aio_offset, aiocb->aio_nbytes);
> if (ret == 0) {
> ret = do_fallocate(s->fd, 0, aiocb->aio_offset,
> aiocb->aio_nbytes);
> if (ret == 0 || ret != -ENOTSUP) {
> return ret;
> }
> s->has_fallocate = false;
> } else if (ret != -ENOTSUP) {
> return ret;
> } else {
> s->has_discard = false;
> }
> }
> #endif
And unmap is translated to "punch hole", too.
In block/raw-posix.c:handle_aiocb_discard():
> #ifdef CONFIG_FALLOCATE_PUNCH_HOLE
> ret = do_fallocate(s->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> aiocb->aio_offset, aiocb->aio_nbytes);
> #endif
So I agree that NBD_CMD_FLAG_NO_HOLE is a poorly named flag, because there is
always going to be a hole event if it's set.
Fam
