如何在C中为非内核应用程序指定内核头文件的路径？

Question

I need to transfer fixp_t typed number (defined at <linux/fixp-arith.h> , originally s16 ) from kernel module to client app using ioctl . Data types are very important, if variable size will differ - results can be very dangerous.

If i include <linux/fixp-arith.h> in both kernel and client app source code, client app fails to compile, because it can't find linux headers.

From other hand, gcc -I/usr/src/linux-headers-3.16.0-4-common/include/ app.c -o app does not work, because <linux/types.h> re-defines existing types and compilation fails.

From other hand, i am scared to specify any data type by myself, because on every arch s16 , and so fixp_t may be different.

How is it possible to workaround this?

Answer 1

From the gcc man page:

-I dir Add the directory dir to the list of directories to be searched for header files.

So, to add the directory you would use:

-I /usr/src/linux-headers-3.16.0-4-common/include/

However, I don't think user space programs are supposed to include kernel headers. If your kernel module has a user space API, then that API should be declared in a header that is separate from the kernel headers and that relies only on standard header files.

Answer 2

Define your own ioctl using what you want.
The specific header will be crafted so that can be included in both app and kernel.
Kernel modules, compiled against kernel headers, will do the correct conversion.