re: Implement mode_select for atapi tape drives - round 4

[Paul Goyette <paul%whooppee.com@localhost>]

On Mon, 10 Aug 2009, matthew green wrote:

>   > +        u_int select_len;
>   > +        struct select {
>   > +                struct scsi_mode_parameter_header_6 header;
>   > +                struct scsi_general_block_descriptor blk_desc;
>   > +                u_char sense_data[MAX_PAGE_0_SIZE];
>   > +        } select;
>   > +        struct scsipi_periph *periph = st->sc_periph;
>   > +
>   > +        select_len = sizeof(select.header) + sizeof(select.blk_desc) +
>   > +                     st->page_0_size;
>   >
>   > should select be __packed?
>
>   Yes, it should probably be. I know most hardware structures are not
>   declared __packed in the scsipi code, we've been luky this didn't cause
>   issues for now ...
>
>
> are these structures used heavily?  __packed will significantly
> slow down accesses to and from them.

These specific structures aren't used frequently, but their member 
structures (especially the struct scsi_general_block_descriptor) are 
members of many others which are more frequently used.



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