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

Post by mikeash » Thu, Nov 02, 2017, 1:27 PM UTC

acobster wrote: post #62

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…

Minor point, but he puts Python in with software that "almost never breaks" on update. Really? Am I missing something? Maybe he just hasn't tried running Python 3 yet...

Post by sleepychu » Thu, Nov 02, 2017, 1:27 PM UTC

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?

    "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."

Post by hasenj » Thu, Nov 02, 2017, 1:29 PM UTC

chii wrote: post #49

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 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…

Post by dingo_bat » Thu, Nov 02, 2017, 1:33 PM UTC

Cthulhu_ wrote: post #59

orcdork wrote: post #14

In any other kind of social/business arrangement he would be politely but firmly escorted out, possibly by security, for this kind of behavior. Being right or wrong is irrelevant.

Even when he's effectively CEO, visionary, and end-responsible for the business? He's the Big Boss of Linux, there is nobody above him in the chain of command. You're used to traditional businesses when there is no single end-responsible person, and when there is a public face for the company (like Jobs, Gates, etc), there is still a group of faceless shareholders above them that can choose to remove them. Not in thi…

Post by jsjohnst » Thu, Nov 02, 2017, 1:34 PM UTC

piker wrote: post #38

__david__ wrote: post #24

Linus's followup post later on in the thread explains his position in more detail and is a pretty good read: http://lkml.iu.edu/hypermail/linux/kernel/1710.3/02487.html

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…