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From: Markus Armbruster <armbru@redhat.com>
Date: Fri, 04 Aug 2017 14:16:41 +0200
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Subject: [Qemu-devel] Is the use of bdrv_getlength() in
 handle_aiocb_write_zeroes() kosher?
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To: "Denis V. Lunev" <den@openvz.org>
Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Kevin Wolf <kwolf@redhat.com>

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.