From Linus Torvalds <> Date Fri, 3 Aug 2018 09:37:35 -0700 Subject Re: LVM snapshot broke between 4.14 and 4.16 [ Dammit. I haven't had to shout and curse at people for a while, but

this is ABSOLUTELY THE MOST IMPORTANT THING IN THE UNIVERSE WHEN IT

COMES TO SOFTWARE DEVELOPMENT ]



On Fri, Aug 3, 2018 at 6:31 AM Zdenek Kabelac <zkabelac@redhat.com> wrote:

>

> IMHO (as the author of fixing lvm2 patch) user should not be upgrading kernels

> and keep running older lvm2 user-land tool (and there are very good reasons

> for this).



Yeah, HELL NO!



Guess what? You're wrong. YOU ARE MISSING THE #1 KERNEL RULE.



We do not regress, and we do not regress exactly because your are 100% wrong.



And the reason you state for your opinion is in fact exactly *WHY* you

are wrong.



Your "good reasons" are pure and utter garbage.



The whole point of "we do not regress" is so that people can upgrade

the kernel and never have to worry about it.



> Kernel had a bug which has been fixed



That is *ENTIRELY* immaterial.



Guys, whether something was buggy or not DOES NOT MATTER.



Why?



Bugs happen. That's a fact of life. Arguing that "we had to break

something because we were fixing a bug" is completely insane. We fix

tens of bugs every single day, thinking that "fixing a bug" means that

we can break something is simply NOT TRUE.



So bugs simply aren't even relevant to the discussion. They happen,

they get found, they get fixed, and it has nothing to do with "we

break users".



Because the only thing that matters IS THE USER.



How hard is that to understand?



Anybody who uses "but it was buggy" as an argument is entirely missing

the point. As far as the USER was concerned, it wasn't buggy - it

worked for him/her.



Maybe it worked *because* the user had taken the bug into account,

maybe it worked because the user didn't notice - again, it doesn't

matter. It worked for the user.



Breaking a user workflow for a "bug" is absolutely the WORST reason

for breakage you can imagine.



It's basically saying "I took something that worked, and I broke it,

but now it's better". Do you not see how f*cking insane that statement

is?



And without users, your program is not a program, it's a pointless

piece of code that you might as well throw away.



Seriously. This is *why* the #1 rule for kernel development is "we

don't break users". Because "I fixed a bug" is absolutely NOT AN

ARGUMENT if that bug fix broke a user setup. You actually introduced a

MUCH BIGGER bug by "fixing" something that the user clearly didn't

even care about.



And dammit, we upgrade the kernel ALL THE TIME without upgrading any

other programs at all. It is absolutely required, because flag-days

and dependencies are horribly bad.



And it is also required simply because I as a kernel developer do not

upgrade random other tools that I don't even care about as I develop

the kernel, and I want any of my users to feel safe doing the same

time.



So no. Your rule is COMPLETELY wrong. If you cannot upgrade a kernel

without upgrading some other random binary, then we have a problem.



Linus



