Re: [Qemu-devel] [RFC PATCH v4 3/4] raw-posix: Add full image preallocation option

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Dec 27, 2013 at 11:05:53AM +0800, Hu Tao wrote:
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index 6f6b8c1..a722d27 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -1160,17 +1160,52 @@ static int64_t raw_get_allocated_file_size(BlockDriverState *bs)
>      return (int64_t)st.st_blocks * 512;
>  }
>  
> +#ifdef __linux__
> +static int raw_preallocate2(int fd, int64_t offset, int64_t length)
> +{
> +    int ret = -1;
> +
> +    ret = fallocate(fd, 0, offset, length);
> +    if (ret < 0) {
> +        ret = -errno;
> +    }
> +
> +    /* fallback to posix_fallocate() if fallocate() is not supported */
> +    if (ret == -ENOSYS || ret == -EOPNOTSUPP) {
> +        ret = posix_fallocate(fd, offset, length);
> +    }
> +
> +    return ret;
> +}

Why is this Linux-specific #ifdef necessary?  glibc will try to use the
fallocate(2) system call, if possible.

Stefan