Date: Wed, 26 Jan 2011 17:55:09 +0000 From: "Robert N. M. Watson" <rwatson@freebsd.org> To: mdf@FreeBSD.org Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r217830 - head/share/man/man9 Message-ID: <12EB1BEA-F0AF-4B2A-AFEB-9C38C7994FA8@freebsd.org> In-Reply-To: <AANLkTimqyPYah5=yWHVxf3Us4=cBYKGkb0oyAE%2B7R-%2Bt@mail.gmail.com> References: <201101251739.p0PHdqKX044842@svn.freebsd.org> <alpine.BSF.2.00.1101260929430.44308@fledge.watson.org> <AANLkTimqyPYah5=yWHVxf3Us4=cBYKGkb0oyAE%2B7R-%2Bt@mail.gmail.com>
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On 26 Jan 2011, at 17:12, mdf@FreeBSD.org wrote: >> Hmm. Is this description missing mention of how wiring failures are >> handled? (Also, it should probably mention that this call can sleep for >> potentially quite long periods of time, even if sbuf_printf (and friends) >> can't). > > I'm not sure how much to write, since some of the wiring failures are > dealt with by the sysctl subsystem and are not documented. > > The current state of the actual code is that a failure in vslock(9) is > ignored, unless it's ENOMEM in which case sysctl_wire_old_buffer sets > the sysctl_req->validlen to 0, which would behave perhaps slightly > unexpectedly for the user since no data will be copied out. > > Any non-ENOMEM failure from vslock() presumably would also have been a > failure from SYSCTL_OUT and this does get squashed, perhaps > incorrectly. > > I'll think about saving the error code so that sbuf_finish can report > it if nothing else has gone wrong. Yeah, no specific opinions on the right answer, except perhaps that sbuf_new_for_sysctl() failing due to ENOMEM is something worth making it easy to report to the user. I suppose an important question is now often we see this actually failing, and in what circumstances: if there's a moderate chance of it failing on low-memory machines under memory pressure, it suggests we've gone wrong somewhere... One nice thing about the non-wiring model is that it's pretty cheap in the common case, whereas the new code is pretty expensive in the common case. Maybe this doesn't matter too much. Roberthome | help
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