 @@ -1,521 +1,548 @@
-.\"	$NetBSD: module.9,v 1.42.2.3 2018/03/11 00:44:32 pgoyette Exp $
+.\"	$NetBSD: module.9,v 1.42.2.4 2018/03/14 02:47:41 pgoyette Exp $
 .\"
 .\" Copyright (c) 2010 The NetBSD Foundation, Inc.
 .\" All rights reserved.
 .\"
 .\" This code is derived from software contributed to The NetBSD Foundation
 .\" by Andrew Doran.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
 .\" are met:
 .\" 1. Redistributions of source code must retain the above copyright
 .\"    notice, this list of conditions and the following disclaimer.
 .\" 2. Redistributions in binary form must reproduce the above copyright
 .\"    notice, this list of conditions and the following disclaimer in the
 .\"    documentation and/or other materials provided with the distribution.
 .\"
 .\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 .\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 .\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 .\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 .\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 .\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 .\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 .\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 .\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd December 16, 2017
+.Dd March 14, 2018
 .Dt MODULE 9
 .Os
 .Sh NAME
 .Nm module ,
 .Nm module_load ,
 .Nm module_autoload ,
 .Nm module_unload ,
 .Nm module_init_class ,
 .Nm module_hold ,
 .Nm module_rele ,
 .Nm module_find_section
 .Nd kernel module loader
 .Sh SYNOPSIS
 .In sys/module.h
 .Fn MODULE "class" "name" "required"
 .Fn MODULE_WITH_ALIAS "class" "name" "required" "aliases"
 .Ft int
 .Fn module_load "const char *name" "int flags" "prop_dictionary_t props" \
 "modclass_t class"
 .Ft int
 .Fn module_autoload "const char *name" "modclass_t class"
 .Ft int
 .Fn module_unload "const char *name"
 .Ft void
 .Fn module_init_class "modclass_t class"
 .Ft int
 .Fn module_hold "const char *name"
 .Ft void
 .Fn module_rele "const char *"
 .Ft int
 .Fn module_find_section "const char *" "void **" "size_t *"
 .Ft void
 .Fn module_init "void"
 .Ft void
 .Fn module_start_unload_thread "void"
 .Ft void
 .Fn module_builtin_require_force "void"
 .Ft void
 .Fn module_load_vfs_init "void"
 .Sh DESCRIPTION
 Modules are sections of code that can be independently linked and selectively
 loaded into or unloaded from a running kernel.
 This provides a mechanism to update the module without having to relink
 the kernel and reboot.
 Modules can be loaded from within the kernel image, provided by the boot
 loader, or loaded from the file system.
 .Pp
 The
 .Nm
 subsystem includes two data types:
 .Bl -enum -offset indent
 .It
 The
 .Vt module_t
 type provides storage to describe a module.
 .It
 The
 .Vt modinfo_t
 type resides within
 .Vt module_t
 and contains module header info.
 .El
 .Pp
 The module subsystem is protected by the global
 .Va kernconfig_mutex .
 .Sh FUNCTIONS
 .Bl -tag -width abcd
 .It Fn MODULE "class" "name" "required"
 .It Fn MODULE_WITH_ALIASES "class" "name" "required" "aliases"
 The
 .Fn MODULE
-macro creates and initializes a
+and
 .Fn MODULE_WITH_ALIASES
 macros create and initialize a
 .Vt modinfo_t
 structure.
 The
 .Fa class
 argument identifies the class of module, and must be one of the following:
 .Bl -tag -width MODULE_CLASS_SECMODEL -offset indent
 .It Dv MODULE_CLASS_VFS
 The module provide a virtual file system - see
 .Xr vfs 9
 .It Dv MODULE_CLASS_DRIVER
 The module is a device driver - see
 .Xr driver 9
 .It Dv MODULE_CLASS_EXEC
 The module provides an alternate execution environment - see the various
 .Dv COMPAT_xxx
 options in
 .Xr options 4
 .It Dv MODULE_CLASS_SECMODEL
 The module provides a security model - see
 .Xr secmodel 9
 .It Dv MODULE_CLASS_BUFQ
 The module provides a buffer queue strategy - see
 .Xr bufq 9
 .It Dv MODULE_CLASS_MISC
 The module provides miscellaneous kernel services
 .El
 .Pp
 The
 .Fa name
 argument provides the name of the module.
 Loaded modules, including those that are built-in to the kernel, must all
 have unique names.
 .Pp
 The
 .Fa required
 argument is a quoted string containing a comma-separated list of module
 names that are required by this module.
 The list must not contain any white-space.
 When a module is loaded, all of its required modules are auto-loaded and
 initialized before the module itself is loaded.
 Loading of required modules is a recursive operation.
 .Pp
-If there are no required modules, this argument should be specified as
+The
 .Fa aliases
 argument is a pointer to a NULL-terminated constant array of constant
 strings.
 Each string in the array is an alternate name (i.e., an alias) of the
 module.
 Module names and aliases must all be unique; a module cannot be loaded
 if its name or any of its aliases matches the name or an alias of any
 already-loaded module.
 (Module names are displayed by the
 .Xr modstat 8
 utility, with an
 .Dv A
 in the flags column.)
 .Pp
 For example,
 .Bd -literal
 	const char * const my_pets[] = { "dog", "cat", "bird", NULL };
 	MODULE_WITH_ALIASES(MODULE_CLASS_MISC, pets, NULL, &my_pets);
 .Ed
 .Pp
 If there are no required modules or aliases, these argument should be
 specified as
 .Dv NULL .
 .Pp
 In addition to the explicit arguments, the
 .Fn MODULE
 macro creates a reference to the module's
 .Fn modcmd
 function.
 This function is defined as:
 .Bl -tag -width modcmd -offset indent
 .It Ft int
 .Fn xxx_modcmd "modcmd_t cmd" "void *data"
 .El
 .Pp
 (where xxx is the name of the module, from the
 .Dv MODULE
 macro).
 .Pp
 The
 .Fa cmd
 argument requests one of the following operations:
 .Bl -tag -width MODULE_CMD_AUTOUNLOAD -offset indent
 .It Dv MODULE_CMD_INIT
 Perform module-specific initialization when the module is loaded.
 .It Dv MODULE_CMD_FINI
 Perform module-specific clean-up before the module is unloaded.
 .It Dv MODULE_CMD_AUTOUNLOAD
 Notify the module that it is about to be unloaded.
 .It Dv MODULE_CMD_STAT
 Request the module to provide status information (not currently implemented).
 .El
 .Pp
 All modules'
 .Fn modcmd
 functions must implement the
 .Dv MODULE_CMD_INIT
 and
 .Dv MODULE_CMD_FINI
 commands.
 The other commands are optional,
 and should return
 .Er ENOTTY
 if not implemented.
 .Pp
 For the
 .Dv MODULE_CMD_INIT
 command, the
 .Fa data
 argument is used to pass a pointer to the module's
 .Xr prop_dictionary 3 .
 For the
 .Dv MODULE_CMD_STAT
 command, the
 .Fa data
 argument points to a buffer where the status information should be placed.
 .Pp
 The __link_set mechanism is used to enable the
 .Nm
 subsystem to locate the
 .Vt modinfo_t
 structure.
 .It Fn module_load "name" "flags" "props" "class"
 Load a module, link it into the running kernel, and call the module's
 .Fn modcmd
 routine with a
 .Fa cmd
 argument of
 .Dv MODULE_CMD_INIT .
 If the specified module requires other modules, they are loaded first; if
 any required module cannot be loaded or if any of their
 .Fn modcmd
 control routines returns a non-zero status, loading of this module and
 the specific required module will fail.
 The required modules are marked for automatic unloading.
 Thus, if the loading of the module failed, the required modules will
 be automatically unloaded after a short delay.
 .Pp
 The loader will look first for a built-in module with the specified
 .Fa name
 that has not been disabled (see
 .Fn module_unload
 below).
 If a built-in module with that
 .Fa name
 is not found, the list of modules prepared by the boot loader is searched.
 If the named module is still not found, an attempt is made to locate the
 module within the file system, provided it has been mounted by the
 initialization code.
 .Pp
 The
 .Fa flags
 argument can include:
 .Bl -tag -width MODCTL_LOAD_FORCE -offset indent
 .It Dv MODCTL_NO_PROP
 When loading a module from the file system, do not attempt to locate a
 corresponding prop_dictionary file.
 .It Dv MODCTL_LOAD_FORCE
 Force loading of disabled built-in modules and modules built for a
 different version of the operating system.
 .El
 .Pp
 The
 .Fa props
 argument points to an externalized property list which is passed to the
 module's
 .Fn modcmd
 routine.
 If a module is being loaded from the file system, and the
 .Dv MODCTL_NO_PROP
 flag is not set, the system searches for a file with the same name as the
 module file, but with the suffix
 .Dq Pa .plist .
 If this file is found, the prop_dictionary it contains is loaded and
 merged with the prop_dictionary from the
 .Fa props
 argument.
 .Pp
 The
 .Fa class
 argument can be any of:
 .Pp
 .Bl -tag -width MODULE_CLASS_SECMODEL -offset indent -compact
 .It Dv MODULE_CLASS_ANY
 .It Dv MODULE_CLASS_DRIVER
 Device driver
 .It Dv MODULE_CLASS_EXEC
 Executable image handler
 .It Dv MODULE_CLASS_MISC
 Miscellaneous module
 .It Dv MODULE_CLASS_SECMODEL
 Security model (see
 .Xr secmodel 9
 for more details)
 .It Dv MODULE_CLASS_VFS
 Virtual file system
 .El
 .Pp
 If the class is not
 .Dv MODULE_CLASS_ANY ,
 the class of the module being loaded
 must match the requested
 .Fa class .
 Except when verifying a module's class when it is being loaded, module
 classes other than
 .Dv MODULE_CLASS_SECMODEL
 are transparent to the module subsystem.
 They are provided only for the benefit of the subsystem's clients.
 Modules with class
 .Dv MODULE_CLASS_SECMODEL
 are automatically registered with
 .Fn secmodel_register
 after being successfully loaded, and automatically deregistered with
 .Fn secmodel_deregister
 when being unloaded.
 .Pp
 The
 .Fn module_load
 routine is primarily intended as the implementation of the
 .Dv MODCTL_LOAD
 option of the
 .Xr modctl 2
 system call.
 .It Fn module_autoload "name" "class"
 Auto-load a module, making it available for automatic unloading.
 The
 .Fa name
 and
 .Fa class
 arguments are the same as for the
 .Fn module_load
 routine.
 .Pp
 The module subsystem uses a kernel thread to attempt to automatically
 unload modules a short time (currently, 10 seconds) after being loaded by
 .Fn module_autoload .
 Before the module is unloaded, its
 .Fn modcmd
 is called with the
 .Fa cmd
 argument specified as
 .Dv MODULE_CMD_AUTOUNLOAD .
 A module can prevent itself from being unloaded by returning a non-zero
 value.
 .Pp
 The
 .Fn module_autoload
 function is intended for use by kernel components to locate and load optional
 system components.
 The function is also used to load modules that are required by other modules.
 .Pp
 The directory from which the module is loaded will be searched for a file
 with the same name as the module file, but with the suffix
 .Dq Pa .plist .
 If this file is found, the prop_dictionary it contains will be loaded and
 passed to the module's
 .Fn modcmd
 routine.
 If this prop_dictionary contains a
 .Dq Pa noautoload
 property which is set to
 .Dq Pa true
 then the system will refuse to load the module.
 .It Fn module_unload "name"
 Unload a module.
 If the module's reference count is non-zero, the function returns
 .Er EBUSY .
 Otherwise, the module's
 .Fn modcmd
 routine is called with a
 .Fa cmd
 argument of
 .Dv MODULE_CMD_FINI .
 If the
 .Fn modcmd
 routine returns with an error, then the error is returned to the caller
 otherwise the module is unloaded.
 .Pp
 The reference counts of all modules that were required by this module are
 decremented, but the required modules are not unloaded by the call to
 .Fn module_unload .
 Instead, the required modules may be unloaded by subsequent calls to
 .Fn module_unload .
 .Pp
 Unloading a built-in module causes the module to be marked as disabled.
 This prevents the module from being re-loaded, except by the
 .Fn module_load
 function with the
 .Fa flags
 argument set to
 .Dv MODULE_FORCE_LOAD .
 .Pp
 The
 .Fn module_unload
 function may be called by the
 .Xr modctl 2
 system call, by the module subsystem's internal auto-unload thread, or by
 other kernel facilities.
 Generally, other kernel facilities should not be calling this function.
 .It Fn module_init_class "class"
 Load and initialize all available modules of the specified
 .Fa class .
 Any built-in modules that have not been disabled, and any modules provided
 by the boot loader are loaded.
 .It Fn module_hold "name"
 Increment the reference count of a module.
 A module cannot be unloaded if its reference count is non-zero.
 .It Fn module_rele "name"
 Decrement the reference count of a module.
 .It Fn module_find_section "name" "addr" "size"
 Find the start address and size of linker section
 .Ar name
 within a module.
 The miniroot module uses this routine to find the address and size of the
 embedded file system image.
 This routine can only examine the linker data for the module that is
 currently being initialized;  it cannot examine data for any other module.
 .It Fn module_init "void"
 Initialize the module subsystem.
 Creates and initializes various data structures, locates all built-in
 modules, and establishes the sub-system's
 .Xr sysctl 8
 tree.
 .Fn module_init
 is called early in system initialization to facilitate use of security model
 modules.
 .It Fn module_start_unload_thread "void"
 Create the thread that attempts to automatically unload modules that were
 loaded via the
 .Fn module_autoload
 routine.
 The function is called only once,
 after the scheduler and timer functions are initialized.
 .It Fn module_builtin_require_force "void"
 Mark as "disabled" any built-in modules that have not been successfully
 initialized.
 Modules marked "disabled" can only be loaded if the
 .Dv MODCTL_LOAD_FORCE
 is specified.
 .Fn module_builtin_require_force
 is called near the end of system initialization, after the
 .Xr init 8
 process is created.
 .It Fn module_load_vfs_init
 The module subsystem is initialized early, long before any file systems
 are available.
 After the root file system is mounted,
 .Fn module_load_vfs_init
 is used to enable loading modules from the file system.
 Until this routine is called, modules can only be loaded if they were
 built-in to the kernel image or provided by the boot loader.
 .El
 .Sh PROGRAMMING CONSIDERATIONS
 The module subsystem is designed to be called recursively, but only within
 a single LWP.
 This permits one module's
 .Fn modcmd
 routine to load or unload other modules.
 .Pp
 Additional considerations:
 .Bl -bullet -offset indent
 .It
 A module is not permitted to load or unload itself.
 Attempts to load or unload a module from within its own
 .Fn modcmd
 routine will fail with
 .Er EEXIST
 or
 .Er EBUSY ,
 respectively.
 .It
 Although a module can be loaded by using either
 .Fn module_load
 or
 .Fn module_autoload ,
 it is not possible for the module's
 .Fn modcmd
 routine to distinguish between the two methods.
 Any module which needs to ensure that it does not get auto-unloaded must
 either handle the
 .Dv MODULE_CMD_AUTOUNLOAD
 command in its
 .Fn modcmd
 routine, or use
 .Fn module_hold
 to increment its reference count.
 Note however that modules loaded manually with
 .Xr modload 8
 are never auto-unloaded.
 .El
 .Sh EXAMPLES
 A set of example modules is available in the
 .Pa src/sys/modules/examples
 directory hierarchy.
 .Sh CODE REFERENCES
 The core of the kernel module implementation is in
 .Pa sys/kern/kern_module.c
 and
 .Pa sys/kern/kern_module_vfs.c .
 .Pp
 The routines for linking the module are in
 .Pa sys/kern/subr_kobj.c .
 .Pp
 The routines for reading a module from the file system are in
 .Pa sys/kern/subr_kobj_vfs.c .
 .Pp
 The header file
 .In sys/sys/module.h
 describes the public interface.
 .Pp
 In addition, each architecture is expected to provide
 .Fn kobj_machdep ,
 .Fn kobj_reloc ,
 and
 .Fn module_init_md .
 .Fn kobj_machdep
 is for any machine dependent actions, such as flushing caches, that are
 needed when a module is loaded or unloaded.
 .Fn kobj_reloc
 deals with resolution of relocatable symbols.
 .Fn module_init_md
 is for finding modules passed in by the boot loader.
 .Sh SEE ALSO
 .Xr modctl 2 ,
 .Xr module 7 ,
 .Xr intro 9lua
 .Sh HISTORY
 The kernel module subsystem first appeared in
 .Nx 5.0 .
 It replaces the
 .Dq LKM
 subsystem from earlier releases.
 .Sh AUTHORS
 .An -nosplit
 The
 .Nm
 system was written by
 .An Andrew Doran Aq Mt ad@NetBSD.org .
 This manual page was written by
 .An Paul Goyette Aq Mt pgoyette@NetBSD.org .