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This may be a simple question but, I heard that the only rule in working on the kernel is that you don't break "user space". So I was wondering what that means: To break user space and how does it happen?
Edit
It has been pointed out to me that this question is not suited for Stack Over Flow by @lurker so I will move it to Super User as @lurker suggests. (See below)
"Questions about general computing hardware and software are off-topic for Stack Overflow unless they directly involve tools used primarily for programming. You may be able to get help on Super User." – lurker, jww, SilentKiller
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That means anything that impacts the user applications in a way that negatively affects its behavior (causes the program to malfunction).
In a computer operating system, user space is the portion of memory containing unprivileged processes run by a user. It is strictly separated from kernel space, the portion of memory where privileged operating system kernel processes are executed. This separation of user and kernel space is called privilege separation.
User space refers to all of the code in an operating system that lives outside of the kernel.
Windows gives each user-mode application a block of virtual addresses. This is known as the user space of that application. The other large block of addresses, known as system space or kernel space, cannot be directly accessed by the application.
You're referring to Linus Torvald's first rule of kernel development. This note explains it: https://lkml.org/lkml/2012/12/23/75. I.e., when maintaining the kernel, do not do something which breaks user programs/applications. In other words, when making kernel changes, it is very bad to cause problems in the user's application "space". That doesn't literally mean memory. That means anything that impacts the user applications in a way that negatively affects its behavior (causes the program to malfunction). The note I cite also indicates at least one example.
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