Access TCP Header Flags via accessor MACRO

[rscheff]

Summary

In order to consistently provide access to all
(including reserved) TCP header flag bits,
use the accessor macros TCP_GET/SET_FLAGS, and
expand any uint8_t / char to at least 16 bit
width.

This is in preparation of AccECN (using one of
the reserved flags)

[rscheff]

• fix typo

[rscheff]

Has anyone else an opinion on the accessor macros?

This revision is effectively replacing it all over the place - including where it is not strictly required.

I could also do a change which only makes use of there, where the ECN / AccECN flags are getting accessed, in order to make the change smaller, and if the compiler doesn't emit efficient code (th_x2 and th_flags may not actually be continous in memory, thus requiring a couple bit shifts wherever the macro is in use).

[tuexen]

sys/netinet/tcp.h

77 ↗

(On Diff #102219)

C question: th_x2 is part of a unsigned char. Doesn't shifting it 8 steps to the left basically clear it? In other words: Don't you need to cast it to uint16_t first? Why is this code working?

[glebius]

If we make these static inline functions instead of macros, we would be able to catch with compiler cases when improper type of flags is used.

[rscheff]

• use static inline function instead of macro
• replace all macro references

[rscheff]

@glebius Good hint.

I put the static inline function into tcp_var.h, where similar other functions already live.

All the accesses to th->th_flags should be covered, some function parameters got extended from uint8_t to uint16_t.

sys/netinet/tcp.h

77 ↗

(On Diff #102219)

I guess it would cast it to int automagically. But I added an explicit cast in the inline function now. thx.

[• hselasky]

sys/netinet/tcp_var.h

1262

const struct tcphdr *th ??

[rscheff]

• use const struct for best compiler optimization in tcp_get_flags

[rscheff]

fixed.

[glebius]

sys/netinet/tcp_var.h

1261

Can we return uint16_t from this function? That of course may require changing type of the argument in several calling functions. But if we are on code improving crusade, why not? :)

[rscheff]

• make tcp_get_flags return an uint16_t

[rscheff]

sys/netinet/tcp_var.h

1261

Sure. Where the function parameter definitions matter, I addressed this already; the local "flags" or "thflags" is mostly defined as an int (not a uint16_t). If that shoud be addressed too, I'd probably do this in another diff, though.

[glebius]

sys/netinet/tcp_var.h

1264

The cast should also be uint16_t, as the whole function, its arguments and return type are unsigned. If I'm not missing anything that will also remove any implicit conversions to the return type.

[rscheff]

• fix typecasting oversight