Constant IOC_SIZEBITS 

pub const IOC_SIZEBITS: usize = 14;

The number of bits used to represent the size of the argument to the ioctl(2) call.

For Alpha (not supported by Rust), MIPS, and PowerPC, this is 13 bits. For all other architectures, this is 14 bits.

For SPARC, this is 14 bits with an overlap on the direction field.

References:

• Alpha: arch/alpha/include/uapi/asm/ioctl.h
• MIPS: arch/mips/include/uapi/asm/ioctl.h
• PowerPC: arch/powerpc/include/uapi/asm/ioctl.h
• All others: include/uapi/asm-generic/ioctl.h