Re: [Xen-devel] [PATCH RFC] xen-block: correctly definestructures in public headers

[Jan Beulich]

>>> On 03.12.13 at 11:57, Roger Pau Monne <roger.pau@xxxxxxxxxx> wrote:
>  struct blkif_request_rw {
>  	uint8_t        nr_segments;  /* number of segments                   */
>  	blkif_vdev_t   handle;       /* only for read/write requests         */
> -#ifdef CONFIG_X86_64
> -	uint32_t       _pad1;	     /* offsetof(blkif_request,u.rw.id) == 8 */
> -#endif
>  	uint64_t       id;           /* private guest value, echoed in resp  */
>  	blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
>  	struct blkif_request_segment {
> @@ -157,47 +154,36 @@ struct blkif_request_rw {
>  		/* @last_sect: last sector in frame to transfer (inclusive).     */
>  		uint8_t     first_sect, last_sect;
>  	} seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> -} __attribute__((__packed__));
> +};

Removing the packed attribute here and below is not possible
as long as the defined structures get used in struct blkif_request
as the second field after a uint8_t one, and as long as the
individual fields here aren't natively aligned.

Jan

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