On Thu, Jan 18, 2007 at 12:10:55AM -0700, Eric W. Biederman wrote:
> Vivek Goyal <[email protected]> writes:
> >
> > Or how about making physical_dest field also 8bit like logical_dest field.
> > This will work both for 4bit and 8bit physical apic ids at the same time
> > code becomes more intutive and it is easier to know whether IOAPIC is being
> > put in physical or destination logical mode.
>
> Exactly what I was trying to suggest.
>
> Looking closer at the code I think it makes sense to just kill the union and
> stop the discrimination between physical and logical modes and just have a
> dest field in the structure. Roughly as you were suggesting at first.
>
> The reason we aren't bitten by this on a regular basis is the normal code
> path uses logical.logical_dest in both logical and physical modes.
> Which is a little confusing.
>
> Since there really isn't a distinction to be made we should just stop
> trying, which will make maintenance easier :)
>
> Currently there are several non-common case users of physical_dest
> that are probably bitten by this problem under the right
> circumstances.
>
> So I think we should just make the structure:
>
> struct IO_APIC_route_entry {
> __u32 vector : 8,
> delivery_mode : 3, /* 000: FIXED
> * 001: lowest prio
> * 111: ExtINT
> */
> dest_mode : 1, /* 0: physical, 1: logical */
> delivery_status : 1,
> polarity : 1,
> irr : 1,
> trigger : 1, /* 0: edge, 1: level */
> mask : 1, /* 0: enabled, 1: disabled */
> __reserved_2 : 15;
>
> __u32 __reserved_3 : 24,
> __dest : 8;
> } __attribute__ ((packed));
>
> And fixup the users. This should keep us from getting bit by this bug
> in the future. Like when people start introducing support for more
> than 256 cores and the low 24bits start getting used.
>
> Or when someone new starts working on the code and thinks the fact
> the field name says logical we are actually using the apic in logical
> mode.
This makes perfect sense to me. Ben, interested in providing a patch
for this?
Thanks
Vivek
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