Date: Wed, 19 Jan 2011 15:26:34 -0800 From: mdf@FreeBSD.org To: Alfred Perlstein <alfred@freebsd.org> Cc: FreeBSD Arch <freebsd-arch@freebsd.org> Subject: Re: Weed-whacking sysctl(8) Message-ID: <AANLkTik49QK0hcFxuPPB9iikSxRoRbpw19r=U6HS7SN2@mail.gmail.com> In-Reply-To: <20110119205445.GX21872@elvis.mu.org> References: <AANLkTimMsy9J5Ohj0pifZ%2B9L4_mFq5z2FwUhG8y5%2B3Kh@mail.gmail.com> <20110119205445.GX21872@elvis.mu.org>
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On Wed, Jan 19, 2011 at 12:54 PM, Alfred Perlstein <alfred@freebsd.org> wro= te: > * mdf@FreeBSD.org <mdf@FreeBSD.org> [110119 12:28] wrote: >> 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'd say that it's not great to break either system. > > The reason is that either the syscall or cmd line utility can be > the basis of numerous system monitoring tools. > > By breaking either interface we discourage people from using it. > > I apologize for coming in so late, but why is CTLTYPE_KELVIN such > an awful thing? Mostly because it's relatively unused, and except for three acpi_thermal instances it's read-only. I wasn't able to find any tools in the tree that knew what format these are in, and as someone else pointed out the units aren't part of any documentation either. > Also, not to digress, but it sounds like there's a rototilling of > the KPI going on here as well that might break 3rd parties who do > their own monitoring software. So far I don't believe I have changed any KPI except for if someone had a custom handler for a QUAD. I would like to do so at some point as 99% of SYSCTL set-up uses OID_AUTO, and it should be 100% but for some legacy code. > Overall it's not a big thing, but when you consider all the changes > like this that go on, it can add up to a discouraging target to > track. > > Honestly I don't have a strong opinion on this and feel free to use > your best judgement and as well as what other people bring to the > table, I just wanted to bring the software churn issue up and > leave the question, "is there a way to do this with minimal 3rd party > breakage". Existing uses of the standard SYSCTL_[ADD_]FOO can be made backwards compatible for a release or so, with minimal effort on my part. It makes the tree a little uglier for a while, though. I was involved with a FreeBSD merge at $WORK from 6.1 to stable/7 and there was a decent bit of change in there. For my part, I preferred a nice clean compile-break to something that still compiled but wasn't the right way to do things going forward. Thanks, matthew
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