Messages in this thread | | | Date | Mon, 18 Oct 2010 16:23:15 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH 1/2] x86: Cleanup TIF value gaps in shift range |
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On 10/18/2010 03:00 PM, David Rientjes wrote: >> >> YES IT IS. In fact, it is completely and totally bananas bonkers. >> >> By not pushing for a proper maintainable ABI, you will have an >> indefinite forward compatibility problem, and when predictably it >> breaks, you'll complain. This is, however, backwards -- the right thing >> would have been to say "I need this, this isn't available, I should add >> a maintainable API and push it upstream", and perhaps add log parsing as >> a backwards-compatibility solution. > > The problem is deciding what should be an ABI and what shouldn't an ABI > when it isn't clear. It would be great if everything that is logged or > shown to userspace would be part of an ABI and would be available no > matter how much information is emitted to the log. That's not scalable, > so we have to decide what userspace may depend on and design ABIs that > provide that information in an extendable way that won't break or become > obsoleted in the foreseeable future. > > Since we can't do that for everything and we have no idea what users will > find to parse from the dmesg, I'm advocating that if a change is proposed, > like was in this case with ti->flags, and someone has a usecase where the > information isn't available in any other way, that they speak up and come > up with a maintainable solution so that we've identified the parties > involved and can change that log message if necessary. I only think that > should be done, though, when there is a compelling reason for the change. > > I think that was done in this case by suggesting an alternative (printing, > at minimum, "M" when a thread has TIF_MEMDIE set instead of the raw flag > bits), but I don't think the change itself was compelling enough that it > has to be done. That doesn't mean doing the change I suggested wasn't > still appropriate, but at least it was known as a prerequisite before > something like this should be merged.
Note: I have already said we shouldn't change TIF_ flags. The thing I'm objecting to is that in very short order you have made multiple requests for API-type stability for things that are explicitly for human consumption, like dmesg and Sysrq information.
Expecting *anything* in dmesg to remain stable in any way is aggravated insanity and completely unreasonable.
-hpa
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