Re: [Qemu-devel] [PATCH] block/raw-posix.c: add BLKDISCARD support

[Stefan Hajnoczi]

On Fri, Nov 11, 2011 at 8:56 PM, e-t172 <address@hidden> wrote:
> +static int hdev_co_discard(BlockDriverState *bs, int64_t sector_num,
> +                        int nb_sectors)
> +{
> +    BDRVRawState *s = bs->opaque;
> +    int fd = s->fd;
> +    uint64_t range[2];
> +
> +    range[0] = sector_num << 9;
> +    range[1] = nb_sectors << 9;
> +    if (ioctl(fd, BLKDISCARD, &range)) {
> +        return -errno;
> +    }
> +    return 0;
> +}

Is ioctl(BLKDISCARD) guaranteed non-blocking?  I think we need to use
paio_ioctl() here instead to do this asynchronously.

Let's also be careful about Linux-specific ioctls.  This code should
not poke an unsupported ioctl() on OSes which do not support
BLKDISCARD.  We definitely need a plan when #if !defined(__linux__).

Stefan