it's in C. as it was explained to me once, the compiler team asked the kernel team if they would be fine fixing C support at C89 and the kernel team said "sure"

it's in C. as it was explained to me once, the compiler team asked the kernel team if they would be fine fixing C support at C89 and the kernel team said "sure". being the largest and most important consumer of the compiler (at the time, possibly still today) that was that. the kernel team is also pretty slow to adapt new C compilers and you can see this by watching the lag in compiler versions released in the driver development kit vs those released with visual studio.