Messages in this thread | | | From | David Howells <> | Subject | [RFC] Splitting kernel headers and deprecating __KERNEL__ | Date | Thu, 25 Nov 2004 15:13:12 +0000 |
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We've been discussing splitting the kernel headers into userspace API headers and kernel internal headers and deprecating the __KERNEL__ macro. This will permit a cleaner interface between the kernel and userspace; and one that's easier to keep up to date.
What we've come up with is this:
(1) Create new directories in the linux sources to shadow existing include directories:
NEW DIRECTORY DIRECTORY SHADOWED ============= ================== include/user/ include/linux/ include/user-*/ include/asm-*/
Note that this doesn't take account of the other directories under include/, but I don't think they're relevant.
(2) Take each file from the shadowed directory. If it has any userspace relevant stuff, then:
(a) Transfer this stuff into a file of the same name in the new directory. So, for example, the syscall number list from include/asm-i386/unistd.h will be transferred to include/user-i386/unistd.h.
(b) Make kernel file #include the user file. So:
[include/asm-i386/unistd.h] ... #include <user-i386/unistd.h> ...
(c) Where a user header file requires something from another header file (such as a type), that file should include a suitable user header file directly:
[include/user-i386/termio.h] ... #include <user/types.h> ...
(d) stdint types should be used where possible.
[include/user-i386/termios.h] struct winsize { uint16_t ws_row; uint16_t ws_col; uint16_t ws_xpixel; uint16_t ws_ypixel; };
(e) These header files should be bounded with __USER_XXXXX_H conditionals:
[include/user-i386/termios.h] #ifndef __USER_I386_TERMIOS_H #define __USER_I386_TERMIOS_H ... #endif /* __USER_I386_TERMIOS_H */
(3) Remove all #if(n)def __KERNEL__ clauses.
(4) Remove the -D__KERNEL__ from the master kernel Makefile.
(5) For userspace use (such as for glibc), the appropriate include/user*/ directories should be selected and installed in /usr/include/ or wherever, and symlinks made. For example, on i386 arch boxes, you might find:
SOURCE INSTALLED AS ====================== ============ include/user/ /usr/include/user/ include/user-i386/ /usr/include/user-i386/ /usr/include/linux -> user /usr/include/asm -> user-i386
(6) On multi-arch archs (such as ppc64 which can also support ppc), you might find:
SOURCE INSTALLED AS ====================== ============ include/user/ /usr/include/user/ include/user-ppc/ /usr/include/user-ppc/ include/user-ppc64/ /usr/include/user-ppc64/ /usr/include/linux -> user /usr/include/asm-ppc -> user-ppc /usr/include/asm-ppc64 -> user-ppc64
And then /usr/include/asm/ might contain files that do arch-size dependent switching between user-ppc and user-ppc64.
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