linux-kernel - Re: [PATCH v4 1/1] virt: acrn: Mark the uuid field as unused

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Date:   Wed, 16 Nov 2022 12:42:16 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, Fei Li <fei1.li@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v4 1/1] virt: acrn: Mark the uuid field as unused

On Wed, Nov 16, 2022 at 11:22:54AM +0200, Andy Shevchenko wrote:
> After the commits for userspace (see Link tags below) the uuid field is
> not being used in the ACRN code. Update kernel to reflect these changes.
> I.e. we do the following:
> - adding a comment explaining that it's not used anymore
> - replacing the specific type by a raw buffer
> - updating the example code accordingly
> 
> The advertised field confused users and actually never been used. So
> the wrong part here is that kernel puts something which userspace never
> used and hence this may confuse a reader of this code.
> 
> Link: https://github.com/projectacrn/acrn-hypervisor/commit/da0d24326ed6
> Link: https://github.com/projectacrn/acrn-hypervisor/commit/bb0327e70097
> Fixes: 5b06931d7f8b ("sample/acrn: Introduce a sample of HSM ioctl interface usage")
> Fixes: 9c5137aedd11 ("virt: acrn: Introduce VM management interfaces")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Acked-by: Rafael J. Wysocki <rafael@...nel.org>
> ---
> v4: added tag (Rafael), Cc'ed to Greg (missing in the previous version
>     by some reason)
> v3: converted to Link tags (Rafael), explained what was wrong (Rafael)
> v2: added tag (Fei)
> 
>  include/uapi/linux/acrn.h | 5 ++---
>  samples/acrn/vm-sample.c  | 3 ---
>  2 files changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/include/uapi/linux/acrn.h b/include/uapi/linux/acrn.h
> index ccf47ed92500..04fa83647ae5 100644
> --- a/include/uapi/linux/acrn.h
> +++ b/include/uapi/linux/acrn.h
> @@ -12,7 +12,6 @@
>  #define _UAPI_ACRN_H
>  
>  #include <linux/types.h>
> -#include <linux/uuid.h>
>  
>  #define ACRN_IO_REQUEST_MAX		16
>  
> @@ -186,7 +185,7 @@ struct acrn_ioreq_notify {
>   * @reserved0:		Reserved and must be 0
>   * @vcpu_num:		Number of vCPU in the VM. Return from hypervisor.
>   * @reserved1:		Reserved and must be 0
> - * @uuid:		UUID of the VM. Pass to hypervisor directly.
> + * @uuid:		Reserved (used to be UUID of the VM)

If it's reserved, then don't you need to check for 0?

>   * @vm_flag:		Flag of the VM creating. Pass to hypervisor directly.
>   * @ioreq_buf:		Service VM GPA of I/O request buffer. Pass to
>   *			hypervisor directly.
> @@ -198,7 +197,7 @@ struct acrn_vm_creation {
>  	__u16	reserved0;
>  	__u16	vcpu_num;
>  	__u16	reserved1;
> -	guid_t	uuid;
> +	__u8	uuid[16];

You just changed the type here, so what is that going to break in
userspace that depended on this being of a structure type and now it's
an array?

And no other kernel changes needed?  Shouldn't you warn if this field is
set?

thanks,

greg k-h