1============================================= 2Exporting kernel headers for use by userspace 3============================================= 4 5The "make headers_install" command exports the kernel's header files in a 6form suitable for use by userspace programs. 7 8The linux kernel's exported header files describe the API for user space 9programs attempting to use kernel services. These kernel header files are 10used by the system's C library (such as glibc or uClibc) to define available 11system calls, as well as constants and structures to be used with these 12system calls. The C library's header files include the kernel header files 13from the "linux" subdirectory. The system's libc headers are usually 14installed at the default location /usr/include and the kernel headers in 15subdirectories under that (most notably /usr/include/linux and 16/usr/include/asm). 17 18Kernel headers are backwards compatible, but not forwards compatible. This 19means that a program built against a C library using older kernel headers 20should run on a newer kernel (although it may not have access to new 21features), but a program built against newer kernel headers may not work on an 22older kernel. 23 24The "make headers_install" command can be run in the top level directory of the 25kernel source code (or using a standard out-of-tree build). It takes two 26optional arguments:: 27 28 make headers_install ARCH=i386 INSTALL_HDR_PATH=/usr 29 30ARCH indicates which architecture to produce headers for, and defaults to the 31current architecture. The linux/asm directory of the exported kernel headers 32is platform-specific, to see a complete list of supported architectures use 33the command:: 34 35 ls -d include/asm-* | sed 's/.*-//' 36 37INSTALL_HDR_PATH indicates where to install the headers. It defaults to 38"./usr". 39 40An 'include' directory is automatically created inside INSTALL_HDR_PATH and 41headers are installed in 'INSTALL_HDR_PATH/include'. 42 43The kernel header export infrastructure is maintained by David Woodhouse 44<dwmw2@infradead.org>. 45