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Hah! I'd never noticed that it was actually defined that way on many systems (including GNU); POSIX says it should be declared as char sa_data[]; So thank

Hah! I'd never noticed that it was actually defined that way on many systems (including GNU); POSIX says it should be declared as char sa_data[]; So thanks for that! However, I don't think your suggestion as to the reasoning passes muster; (1) the socket interface originated in BSD, where longer filenames already existed, and (2) for AF_UNIX sockets, the data is the full path including directories, not just the base filename. My guess is that sockaddr was originally defined as 16 bytes (2 bytes type, 14 bytes data) just because someone thought it was a nice round number, and that GNU and other systems have kept the "14" to establish a minimum size for the struct, and that in order to avoid breaking historical code that uses sockaddr instead of sockaddr_storage.

LukeShu 6y ago
Looks like "someone" was Bill Joy in November 1981: https://github.com/dspinellis/unix-history-repo/commit/3573c034bb533247ae46756dc370f6edec04d287 https://github.com/dspinellis/unix-history-repo/commit/3573c... And we have a better clue as to why: there was a separate "sockaddri" that allowed for indirect references for address sizes > 14 bytes. So the sa_data[14] comes from 16 bytes being the maximum amount of data that Bill Joy was willing to pass around by value instead of by reference. (Actually, that was probably modeled after the older `struct in_addr`, but the headers for that are missing--so I can't tell. Perhaps it was a design decision carried forward from someone else; perhaps someone from BBN?)