In trying to get the termios2 interface actually implemented in glibc, the question came up if we will ever care about baud rates in excess of 4 Gbps, even in the relatively remote future. If this is something we care about *at all*, I would like to suggest that rather than defining yet another kernel interface, we steal some bits from the MSB of the speed fields, alternatively one of the c_cc bytes (all likearchitectures seem to have c_cc[18] free) or some field, if we can find them, in c_cflags, to indicate an exponent. With 5 bits from the top of the speed fields, the current values would be identical up to 248 Gbps, and values up to ~288 Pbps would be encodable ±2 ppb. In the short term, all we would have to do in the kernel would be erroring out on baud rates higher than 0x0fffffff (2^28-1 due to implicit one aliasing rhe first bit of a 5-bit exponent – less than 2^27 are functionally denorms.) However, I'd like to put the glibc infrastructure for this now if this is something we may ever be interested in. Thoughts? -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
