Re: [Qemu-devel] [RFC PATCH v3 3/6] block/raw-posix: implement bdrv_preallocate

[Stefan Hajnoczi <stefanha@gmail.com>]

On Thu, Dec 19, 2013 at 10:27:38AM +0800, Hu Tao wrote:
> +static int raw_preallocate2(int fd, int64_t offset, int64_t length)
> +{
> +    int ret = -1;
> +
> +    ret = fallocate(fd, 0, offset, length);
> +
> +    /* fallback to posix_fallocate() if fallocate() is not supported */
> +    if (ret < 0 && (errno == ENOSYS || errno == EOPNOTSUPP)) {
> +        ret = posix_fallocate(fd, offset, length);
> +    }
> +
> +    return ret;

Return value semantics differ between the two functions:
 * fallocate - return 0 or -1 with errno set
 * posix_fallocate - return 0 or error number (without using errno!)

Please make it consistent.  Usually in QEMU we return 0 on success and
-errno on failure.