Why the Linux Kernel Discourages Using typedef

When developing Linux drivers, developers may encounter a warning: WARNING: do not add new typedefs. Although only a warning, it becomes a required fix for contributions to the kernel repository.

1. Linus Torvalds' Attitude

Linus Torvalds has expressed that he does not want a "typedef culture" to dominate the kernel, but he does not forbid occasional typedefs. He prefers using struct mystruct because it makes the actual type clearer, though it is not mandatory.

Torvalds recommends the struct mystruct style.

Typedefs can obscure the real type, making code harder to understand.

Given the kernel's massive architecture, typedefs defined for one architecture may not be portable to others.

Original source: https://lkml.indiana.edu/hypermail/linux/kernel/0206.1/0402.html

2. Kernel Coding Style Guidelines

The kernel coding style outlines specific situations where typedefs are acceptable:

Completely opaque objects to hide internal implementation.

Explicit integer types (e.g., u8, u16, u32) to avoid confusion between int and long.

Creating new types that match standard C99 types in special cases.

Types intended for use in user space.

Full guidelines: https://www.kernel.org/doc/html/v4.10/process/coding-style.html

3. Personal Viewpoint

For large projects like the Linux kernel, avoiding excessive typedefs helps prevent type proliferation and improves code readability. In small personal projects, developers can use typedefs at will, as the impact on maintainability is minimal.

Community discussions:

Why use typedef frequently in C? https://stackoverflow.com/questions/252780/why-should-we-typedef-a-struct-so-often-in-c

Why does the Linux kernel coding style discourage typedef? https://www.reddit.com/r/C_Programming/comments/dan8vr/why_does_the_linux_kernel_coding_style_guide/