Re: "Enhanced" MD code avaible for review

[Jamie Lokier <jamie@shareable.org>]

Jeff Garzik wrote:
> I'll probably have to illustrate with code, but basically, read/write 
> can be completely ignorant of 32/64-bit architecture, endianness, it can 
> even be network-transparent.  ioctls just can't do that.

Apart from the network transparency, yes they can.

Ioctl is no different from read/write/read-modify-write except
the additional command argument.

You can write architecture-specific ioctls which take and return
structs -- and you can do the same with read/write.  This is what
Andi is thinking of as dangerous: the read/write case is then much
harder to emulate.

Or, you can write architecture-independent read/write, which use fixed
formats, which you seem to have in mind.  That works fine with ioctls too.

It isn't commonly done, because people prefer the convenience of a
struct.  But it does work.  It's slightly easier in the driver to
implement commands this way using an ioctl, because you don't have to
check the read/write length.  It's about the same to use from
userspace: both read/write and ioctl methods using an
architecture-independent data format require the program to lay out
the command bytes and then issue one system call.

-- Jamie