FreeBSD Manual Pages
KLD(4) Kernel Interfaces Manual KLD(4) NAME kld -- dynamic kernel linker facility DESCRIPTION The LKM (Loadable Kernel Modules) facility has been deprecated in FreeBSD 3.0 and above in favor of the kld interface. This interface, like its predecessor, allows the system administrator to dynamically add and remove functionality from a running system. This ability also helps software developers to develop new parts of the kernel without constantly rebooting to test their changes. Various types of modules can be loaded into the system. There are sev- eral defined module types, listed below, which can be added to the sys- tem in a predefined way. In addition, there is a generic type, for which the module itself handles loading and unloading. The FreeBSD system makes extensive use of loadable kernel modules, and provides loadable versions of most file systems, the NFS client and server, all the screen-savers, and the Linux emulator. kld modules are placed by default in the /boot/kernel directory along with their match- ing kernel. The kld interface is used through the kldload(8), kldunload(8) and kldstat(8) programs. The kldload(8) program can load either a.out(5) or ELF formatted load- able modules. The kldunload(8) program unloads any given loaded mod- ule, if no other module is dependent upon the given module. The kldstat(8) program is used to check the status of the modules currently loaded into the system. Kernel modules may only be loaded or unloaded if the system security level kern.securelevel is less than one. MODULE TYPES Device Driver modules New block and character device drivers may be loaded into the system with kld. Device nodes for the loaded drivers are automatically cre- ated when a module is loaded and destroyed when it is unloaded by devfs(5). You can specify userland programs that will run when new de- vices become available as a result of loading modules, or existing de- vices go away when modules are unloaded, by configuring devd(8). FILES /boot/kernel directory containing module binaries built for the kernel also residing in the direc- tory. /usr/include/sys/module.h file containing definitions required to com- pile a kld module /usr/share/examples/kld example source code implementing a sample kld module SEE ALSO kldfind(2), kldfirstmod(2), kldload(2), kldnext(2), kldstat(2), kldunload(2), devfs(5), devd(8), kldload(8), kldstat(8), kldunload(8), sysctl(8) HISTORY The kld facility appeared in FreeBSD 3.0 and was designed as a replace- ment for the lkm facility, which was similar in functionality to the loadable kernel modules facility provided by SunOS 4.1.3. AUTHORS The kld facility was originally implemented by Doug Rabson <dfr@FreeBSD.org>. BUGS If a module B, is dependent on another module A, but is not compiled with module A as a dependency, then kldload(8) fails to load module B, even if module A is already present in the system. If multiple modules are dependent on module A, and are compiled with module A as a dependency, then kldload(8) loads an instance of module A when any of the modules are loaded. If a custom entry point is used for a module, and the module is com- piled as an `ELF' binary, then kldload(8) fails to execute the entry point. kldload(8) points the user to read dmesg(8) for any error encountered while loading a module. When system internal interfaces change, old modules often cannot detect this, and such modules when loaded will often cause crashes or mysteri- ous failures. FreeBSD 14.3 January 13, 2014 KLD(4)
NAME | DESCRIPTION | MODULE TYPES | FILES | SEE ALSO | HISTORY | AUTHORS | BUGS
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