Date: Wed, 19 Jan 2011 15:20:59 -0800 From: mdf@FreeBSD.org To: jmg@funkthat.com Cc: FreeBSD Arch <freebsd-arch@freebsd.org> Subject: Re: Weed-whacking sysctl(8) Message-ID: <AANLkTikPu3XRaOea-7=qYPehgYx=a9P2gopM=v=BJJDY@mail.gmail.com> In-Reply-To: <20110119214339.GH66284@funkthat.com> References: <AANLkTimMsy9J5Ohj0pifZ%2B9L4_mFq5z2FwUhG8y5%2B3Kh@mail.gmail.com> <20110119214339.GH66284@funkthat.com>
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On Wed, Jan 19, 2011 at 1:43 PM, John-Mark Gurney <jmg@funkthat.com> wrote: > mdf@freebsd.org wrote this message on Wed, Jan 19, 2011 at 12:28 -0800: >> As bde@ mentioned, there's very little actual use of the sysctl format >> strings. =A0I recently changed it so the use is even smaller, but I've >> got a quandary as to how to finish the job. >> >> I agree with Bruce that the formatted structs can just be removed. >> This leaves just the "IK" format, which shows up in just a few files: >> >> sys/dev/acpica/acpi_thermal.c: >> sys/dev/amdtemp/amdtemp.c >> sys/dev/acpi_support/atk0110.c >> sys/dev/coretemp/coretemp.c >> sys/dev/iicbus/max6690.c >> sys/dev/iicbus/ds1775.c >> >> I see two solutions to "IK". =A0The first is to preserve the interface >> as experienced by sysctl(8) users, and add some functions to push a >> string buffer back to userspace, and parse a string in the kernel. >> The second is to preserve the binary interface as experienced by >> sysctl(3) users, and either have the values be dumped in the slightly >> obscure 10ths of Kelvin values, or add a new CTLTYPE_KELVIN so >> sysctl(8) can also keep showing things as it does today. >> >> Given how infrequent the use is CTLTYPE_KELVIN seems a non-starter. >> So who is the worse client to break: those who use sysctl(8) to look >> at temperatures, or those who have a utility to manipulate these >> values using sysctl(3)? > > I've been watching this discussion pretty closely as I recently wrote > a bsnmp module to export sysctl values and ran into the problem of > parsing data exactly how sysctl(8) does it for presentation. > > What about creating a new SYSCTL_KELVIN that is SYSCTL_PROC that > converts that variable in kelvin into 10ths of Kelvin, or as a > floating point value? > > It would break people who were directly parsing sysctl(3) output, but > they were also never quering the type via the undocumented API to get > the correct format and type information in the first place and depending > upon the undocumented type behavior. > > The man pages for acpi_thermal(4), amdtemp(4) and coretemp(4) only > say that the temp is supplied by those sysctl nodes, not the format > nor that they are in the magic 10ths of Kelvin formation. =A0So only > preserving sysctl(8) output would be my vote. =A0(Preserving sysctl(3) > users that properly understands format and/or type would also be best). > > I was about to write a patch to add a function to libc to be able to > get both format string and type, but obviously this has changed a bit > in the last week, and at least the format string part will not be > necessary. IMO it would be nice to have a real API to fetch the type. The sysctl documentation claims it's being thought about, but I think it's said that for several years. :-) The format string was mostly unused and I'd prefer it to die than be used more. Except for the case of "IK" and 4 specially formatted structs, the string provides no new information over the ctltype. Thanks, matthew
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