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A regression is the kernel not giving the same result with the same user space

lkml.iu.edu

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Re: A regression is the kernel not giving the same result with the same user space

#101

Post by jacobush »

caf wrote: post #70
piker wrote: post #38

Earlier quoted context omitted.

Interesting. > Behavioral changes happen, and maybe we don't even support some feature any more. There's a number of fields in /proc/ /stat that are printed out as zeroes, simply because they don't even exist in the kernel any more, or because showing them was a mistake (typically an information leak). But the numbers got replaced by zeroes, so that the code that used to parse the fields still works. The user might n…

If your code had actually broken with the change to a zero (for example it didn't just report 0 of some resource in use in the log, but spawned an unlimited amount of threads until it crashed or something) then you could have reported it as a kernel regression, and it would have been fixed in another way.

True but there is more to it. Linus’s ambition is to also not break the unknown app in the basement, behind the leopard.

Re: A regression is the kernel not giving the same result with the same user space

#102

Post by eternalban »

pjmlp wrote: post #22
jordigh wrote: post #4

Mercurial, made by another (in my opinion) much more well-spoken kernel hacker, is what really introduced me to the concept that you do not break interface for downstream users, no matter how wrongly you may think they are using the interface. It’s an attitude that is difficult to convey because software developers always want to have the freedom to “improve” their own software, even at the possible cost of breaking…

Rich Hickey has a wonderful talk about it. "Spec-ulation" - https://www.youtube.com/watch?v=oyLBGkS5ICk Which I fully agree with, basically there are no major, minor, patch level changes, in reality every change is a possible breaking changes, because we don't control what downstream is doing with our software.

> there are no major, minor, patch level changes, in reality every change is a possible breaking changes

It is "possible" that my blowing my nose will disturb butterflies in China.

Internal to the organization that produces the software, they are highly meaningful. Extended to user base that reads the documentation, it remains equally meaningful.

Downstream that resists information and can not be controlled is on its own. Good luck.

Re: A regression is the kernel not giving the same result with the same user space

#103

Post by bryanlarsen »

delroth wrote: post #45
wolfwyrd wrote: post #43

Earlier quoted context omitted.

It's laid out further in the thread [1]. The key quote comes from Thorsten: > All that afaics doesn't matter. If a new kernel breaks things for people > (that especially includes people that do not update their userland) > then it's a kernel regression, even if the root of the problem is in > usersland. Linus (CCed) said that often enough [1] http://lkml.iu.edu/hypermail/linux/kernel/1710.3/02487.html

Does that mean the kernel is not allowed to change version number anymore because I could write an app that segfaults if it sees Linux >= 4.14?

Windows contains code like "If SimCity is running, allow it to use memory after it's been freed"[1]

So yes, if you had a significantly deployed app that segfaults because the version number >= 4.14, Linux probably would seriously consider workarounds for your app.

1: https://www.joelonsoftware.com/2004/06/13/how-microsoft-lost...

Re: A regression is the kernel not giving the same result with the same user space

#104

Post by [deleted] »

jordigh wrote: post #4

Mercurial, made by another (in my opinion) much more well-spoken kernel hacker, is what really introduced me to the concept that you do not break interface for downstream users, no matter how wrongly you may think they are using the interface. It’s an attitude that is difficult to convey because software developers always want to have the freedom to “improve” their own software, even at the possible cost of breaking…

[deleted]

Re: A regression is the kernel not giving the same result with the same user space

#105

Post by _jal »

delroth wrote: post #78
Ntrails wrote: post #57

Earlier quoted context omitted.

You're just being disingenuous, what does that help? It's clearly an error on the part of the kernel if the owner of said kernel has specific expectations of behaviour on upgrade with respect to user spaces and those are not being met.

It is just as disingenuous as saying "details don't matter". bonzini's comment was saying a line needs to be drawn, and I agree with that. It's pretty clear the line needs to not include "breaking on version number updates", less clear what it also needs to not include.

No, in fact, it is pretty obvious, at least to people doing kernel dev.

The contract in this case is that there will always be a version number, and anyone who expects it not to change is an idiot or just being obtuse.

Re: A regression is the kernel not giving the same result with the same user space

#106

Post by snuxoll »

rkangel wrote: post #60
fdej wrote: post #29

Earlier quoted context omitted.

If only compiler developers had this attitude.

I think Rust has done this quite well, managing to have the best of both worlds. Unstable features are only available on the nightly build and need specifically enabling (and their interface may change). Once a feature is considered stable it is carefully maintained. They do have some breaking changes, but they're not common and for unusual edge cases: https://killercup.github.io/bitrust/ This explains the Rust appro…

Rust also has yet to develop a stable ABI, I know they’re hard at work on so many things so I don’t say this as some snide remark - but until this is the case and Rust supports proper dynamic linking there’s whole domains of tasks I’m not comfortable using it for.

Re: A regression is the kernel not giving the same result with the same user space

#107

Post by [deleted] »

hyperpape wrote: post #74
chii wrote: post #49

Earlier quoted context omitted.

> If my application depends on some of those zero'd fields, it seems like that has potential to cause serious debugging problems, as opposed to just causing an error on the parse. if your app didn't used to handle the 'zero' case (assuming zero was a "valid" value for said field), then the app was poorly written and would'be been broken in the first place. However, if the app _did_ handle the 'zero' case, then the ap…

There are many cases where continuing with invalid data is much worse than a parse error. Perhaps that's less likely in this case (hopefully your credit card payment doesn't depend on the values in /proc/ /stat), but as a rule, silently continuing with meaningless data is scary.

[deleted]

Re: A regression is the kernel not giving the same result with the same user space

#108

Post by steveklabnik »

snuxoll wrote: post #106
rkangel wrote: post #60

Earlier quoted context omitted.

I think Rust has done this quite well, managing to have the best of both worlds. Unstable features are only available on the nightly build and need specifically enabling (and their interface may change). Once a feature is considered stable it is carefully maintained. They do have some breaking changes, but they're not common and for unusual edge cases: https://killercup.github.io/bitrust/ This explains the Rust appro…

Rust also has yet to develop a stable ABI, I know they’re hard at work on so many things so I don’t say this as some snide remark - but until this is the case and Rust supports proper dynamic linking there’s whole domains of tasks I’m not comfortable using it for.

I can assure you we’re not actively working on a stable ABI.

Re: A regression is the kernel not giving the same result with the same user space

#109

Post by andyjohnson0 »

dingo_bat wrote: post #81

I'm always eager to read Linus's rants. I wish more of my coworkers were like him. I hate the environment where nobody reacts strongly to anything! If somebody fucks up hard and refuses to own up, I (or whoever's in charge) should be able to shout at them. It's only natural.

I disagree. To me he usually comes across as an asshole, albeit an extremely smart and accomplished one. A working environment where the person at the top can be relied upon to react to human failings with an aggressive, sweary [1] rant is not somewhere I ever want to work.

[1] I'm aware that use of profanity in everyday speech is common in Finland. I don't mind swearing per se, but I find its over-use a bit tedious.

Re: A regression is the kernel not giving the same result with the same user space

#110

Post by vetinari »

magicalhippo wrote: post #92
mikeash wrote: post #71

Earlier quoted context omitted.

Python 3 is a similar language with a similar name to Python 2. It shouldn’t be considered an update, nor applied as one.

Yet the Python 3 executable has the same name as the Python 2 executable...

Only on Arch and Windows... All other Linux distribution have python3 and macOS binary is also python3.
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