bionic (4) kld.4freebsd.gz

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 several defined module types, listed
     below, which can be added to the system 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 iBCS2 and Linux emulators.  kld
     modules are placed by default in the /boot/kernel directory along with their matching 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 loadable modules.  The kldunload(8)
     program unloads any given loaded module, 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 created when a module is loaded and destroyed when it is unloaded by devfs(5).
     You can specify userland programs that will run when new devices become available as a result of loading
     modules, or existing devices 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
                                directory.
     /usr/include/sys/module.h  file containing definitions required to compile 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 replacement 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 compiled 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 mysterious failures.