Re: [Xen-devel] [PATCH] blkif: add indirect descriptors interface to public headers

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.11.13 at 15:12, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> On 12/11/13 13:46, Paul Durrant wrote:
>>> +    uint64_t       id;           /* private guest value, echoed in resp  */
>>> +    blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
>>> +    blkif_vdev_t   handle;       /* same as for read/write requests      */
>>> +    grant_ref_t
>>> indirect_grefs[BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST];
>>> +#ifdef __i386__
>>> +    uint64_t       pad;          /* Make it 64 byte aligned on i386      */
>>> +#endif
> 
> This last field looks a bit odd though.  Why is it needed?

On 64-bit there's a 32 bit hole before "id" and another one at the
end of the structure. In order for the structure size to be as
specified in the comment, both these holes need to be accounted
for.

>>> +};
>>> +typedef struct blkif_request_indirect blkif_request_indirect_t;
>>> +
>>> +struct blkif_request_segment_aligned {
>>> +    grant_ref_t gref;            /* reference to I/O buffer frame        */
>>> +    /* @first_sect: first sector in frame to transfer (inclusive).   */
>>> +    /* @last_sect: last sector in frame to transfer (inclusive).     */
>>> +    uint8_t     first_sect, last_sect;
> 
> Missing uint8_t padding here?

Note that there are _two_ uint8_t-s.

Jan


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