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Re: Implement mode_select for atapi tape drives - round 4

On Sun, 9 Aug 2009, David Laight wrote:

On Sun, Aug 09, 2009 at 09:47:29PM +0200, Manuel Bouyer wrote:

I don't get it. If the hardware (scsi devices in this case) defines
a structure like e.g
struct foo {
        int8_t data1;
        int32_t data2;
        int8_t data3
        int32_t data4;
the software on the host side will have to do misaligned accesses whatever
we do, isn't it ? How do we avoid the compiler from padding the members
without __packed ?

For data2 use __attribute__((__aligned__(1)))
and for data4 __attribute__((__aligned__(2)))

Everything in the particular structures that started this discussion are uint8_t so alignment should be a concern here. Unless, of course, the compiler is allowed to force an array of uint8_t to start on a "nice" boundary.

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