Is bool a native C type?
bool exists in the current C - C99, but not in C89/90.
In C99 the native type is actually called _Bool, while bool is a standard library macro defined in stdbool.h (which expectedly resolves to _Bool). Objects of type _Bool hold either 0 or 1, while true and false are also macros from stdbool.h.
Note, BTW, that this implies that C preprocessor will interpret #if true as #if 0 unless stdbool.h is included. Meanwhile, C++ preprocessor is required to natively recognize true as a language literal.
C99 added a builtin _Bool data type (see Wikipedia for details), and if you #include <stdbool.h>, it provides bool as a macro to _Bool.
You asked about the Linux kernel in particular. It assumes the presence of _Bool and provides a bool typedef itself in include/linux/types.h.
C99 has it in stdbool.h, but in C90 it must be defined as a typedef or enum:
typedef int bool;#define TRUE 1#define FALSE 0bool f = FALSE;if (f) { ... }Alternatively:
typedef enum { FALSE, TRUE } boolean;boolean b = FALSE;if (b) { ... }