On Thu, Mar 18, 2010 at 10:49:01AM -0700, Roland Dreier wrote:
> Including this structure is no problem in principle.
>
> > Could we use the bitfield versions of this I posted awhile back? :)
>
> I don't have that patch handy, but bitfields often end up ugly with
> endian stuff, and also some compilers/architecture generate awful code
> for it. What's the advantage over Sean's patch?
It is user space code, the interface should be trivially usable
without a huge hassle to the user. Bitfields can help provide
that. The LE/BE issue is easy to solve, but I admit the solution I
prefer (32 bit byte swap) might not fit very well with Sean's intended
use.
For instance if you want to override the hoplimit to 1:
pr.flowlabel_hoplimit = htonl((ntohl(pr.flowlabel_hoplimit) & (~0xFF)) | 1);
vs
swap32_all(&pr, sizeof(pr);
pr.hopLimit = 1;
swap32_all(&pr, sizeof(ptr));
For this application I don't think the codegen is a concern, and I've
seen that x86 and ppc generate acceptable code for this.. Certainly,
this approach is definately faster than the pack/unpack scheme I've
seen used in many place.
#ifdef BIG_ENDIAN
struct SAPathRecord {
uint32_t rsv0;
uint32_t rsv1;
uint8_t DGID[16];
uint8_t SGID[16];
uint16_t DLID;
uint16_t SLID;
uint32_t rawTraffic:1;
uint32_t rsv2:3;
uint32_t flowLabel:20;
uint32_t hopLimit:8;
uint8_t TClass;
uint8_t reversible:1;
uint8_t numbPath:7;
uint16_t PKey;
uint16_t rsv3:12;
uint16_t SL:4;
uint8_t MTUSelector:2;
uint8_t MTU:6;
uint8_t rateSelector:2;
uint8_t rate:6;
uint8_t packetLifeTimeSelector:2;
uint8_t packetLifeTime:6;
uint8_t preference;
uint16_t rsv4;
uint32_t rsv5;
};
#else
// Must ntohl() every 32 bit word prior to appling this structure
struct SAPathRecord {
uint32_t rsv0;
uint32_t rsv1;
uint8_t DGID[16];
uint8_t SGID[16];
uint16_t SLID;
uint16_t DLID;
uint32_t hopLimit:8;
uint32_t flowLabel:20;
uint32_t rsv2:3;
uint32_t rawTraffic:1;
uint16_t PKey;
uint8_t numbPath:7;
uint8_t reversible:1;
uint8_t TClass;
uint8_t rate:6;
uint8_t rateSelector:2;
uint8_t MTU:6;
uint8_t MTUSelector:2;
uint16_t SL:4;
uint16_t rsv3:12;
uint16_t rsv4;
uint8_t preference;
uint8_t packetLifeTime:6;
uint8_t packetLifeTimeSelector:2;
uint32_t rsv5;
};
#endif
Jason
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