[Qemu-block] Is the use of bdrv_getlength() in handle_aiocb_write_zeroes() kosher?

[Markus Armbruster]

Denis, you added this in commit d50d822:

#ifdef CONFIG_FALLOCATE
    if (s->has_fallocate && aiocb->aio_offset >= bdrv_getlength(aiocb->bs)) {
        int ret = do_fallocate(s->fd, 0, aiocb->aio_offset, aiocb->aio_nbytes);
        if (ret == 0 || ret != -ENOTSUP) {
            return ret;
        }
        s->has_fallocate = false;
    }
#endif

bdrv_getlength() can fail.  Does it do the right thing then?  For what
it's worth, the comparison of its value is signed.