https://bugzilla.kernel.org/show_bug.cgi?id=178241 Bug ID: 178241 Summary: tcp.7 says SIOCOUTQ counts unsent bytes, but in actually counts unacknowledged bytes Product: Documentation Version: unspecified Hardware: All OS: Linux Status: NEW Severity: normal Priority: P1 Component: man-pages Assignee: documentation_man-pages@xxxxxxxxxxxxxxxxxxxx Reporter: njs@xxxxxxxxx Regression: No tcp.7 says: SIOCOUTQ Returns the amount of unsent data in the socket send queue. [...] I believe that this is incorrect, and that it actually returns the amount of *unacknowledged* data in the socket send queue (i.e., unsent data + data that has been sent, but for which we're still waiting for an ACK). This can be confirmed by looking at the source, which does: 575 answ = tp->write_seq - tp->snd_una; http://lxr.free-electrons.com/source/net/ipv4/tcp.c#L568 here tp->snd_una is the boundary between acknowledged and unacknowledged data. If it were reporting unsent data, it would need to use tp->snd_nxt instead. (The diagram in RFC 793 may help visualize this: https://tools.ietf.org/html/rfc793#page-20) I discovered this while trying to figure out how TCP_NOTSENT_LOWAT works. TCP_NOTSENT_LOWAT makes it so that a socket only becomes writeable if the unsent data is under a certain threshold, yet SIOCOUTQ was reporting that I had more unsent data than that, and yet the socket was still writeable... which makes sense if SIOCOUTQ is not actually reporting the amount of unsent data :-). -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
