Manpages - init_module.2

init_module, finit_module - load a kernel module

  #include <linux/module.h> /* Definition of MODULE_* constants */
  #include <sys/syscall.h> /* Definition of SYS_* constants */
  #include <unistd.h>

  int syscall(SYS_init_module, void *module_image, unsigned long len,
   const char *param_values);
  int syscall(SYS_finit_module, int fd, const char *param_values,
   int flags);

Note: glibc provides no wrappers for these system calls, necessitating the use of *syscall*(2).

*init_module*() loads an ELF image into kernel space, performs any necessary symbol relocations, initializes module parameters to values provided by the caller, and then runs the module’s init function. This system call requires privilege.

The module_image argument points to a buffer containing the binary image to be loaded; len specifies the size of that buffer. The module image should be a valid ELF image, built for the running kernel.

The param_values argument is a string containing space-delimited specifications of the values for module parameters (defined inside the module using *module_param*() and *module_param_array*()). The kernel parses this string and initializes the specified parameters. Each of the parameter specifications has the form:

name[ =*/value/ [,* value…]]

The parameter name is one of those defined within the module using module_param/() (see the Linux kernel source file /include/linux/moduleparam.h). The parameter value is optional in the case of bool and invbool parameters. Values for array parameters are specified as a comma-separated list.

On success, these system calls return 0. On error, -1 is returned and errno is set to indicate the error.

EBADMSG (since Linux 3.7)

Module signature is misformatted.

EBUSY

Timeout while trying to resolve a symbol reference by this module.

EFAULT

An address argument referred to a location that is outside the process’s accessible address space.

ENOKEY (since Linux 3.7)

Module signature is invalid or the kernel does not have a key for this module. This error is returned only if the kernel was configured with CONFIG_MODULE_SIG_FORCE; if the kernel was not configured with this option, then an invalid or unsigned module simply taints the kernel.

ENOMEM

Out of memory.

EPERM

The caller was not privileged (did not have the CAP_SYS_MODULE capability), or module loading is disabled (see /proc/sys/kernel/modules_disabled in *proc*(5)).

The following errors may additionally occur for *init_module*():

EEXIST

A module with this name is already loaded.

EINVAL

param_values is invalid, or some part of the ELF image in module_image contains inconsistencies.

ENOEXEC

The binary image supplied in module_image is not an ELF image, or is an ELF image that is invalid or for a different architecture.

The following errors may additionally occur for *finit_module*():

EBADF

The file referred to by fd is not opened for reading.

EFBIG

The file referred to by fd is too large.

EINVAL

flags is invalid.

ENOEXEC

fd does not refer to an open file.

In addition to the above errors, if the module’s init function is executed and returns an error, then *init_module*() or *finit_module*() fails and errno is set to the value returned by the init function.

*finit_module*() is available since Linux 3.8.

*init_module*() and *finit_module*() are Linux-specific.

The *init_module*() system call is not supported by glibc. No declaration is provided in glibc headers, but, through a quirk of history, glibc versions before 2.23 did export an ABI for this system call. Therefore, in order to employ this system call, it is (before glibc 2.23) sufficient to manually declare the interface in your code; alternatively, you can invoke the system call using *syscall*(2).

Information about currently loaded modules can be found in /proc/modules and in the file trees under the per-module subdirectories under /sys/module.

See the Linux kernel source file include/linux/module.h for some useful background information.

(User-space applications can detect which version of init_module*() is available by calling *query_module*(); the latter call fails with the error *ENOSYS on Linux 2.6 and later.)

The older version of the system call loads the relocated module image pointed to by image into kernel space and runs the module’s init function. The caller is responsible for providing the relocated image (since Linux 2.6, the *init_module*() system call does the relocation).

The module image begins with a module structure and is followed by code and data as appropriate. Since Linux 2.2, the module structure is defined as follows:

  struct module {
      unsigned long         size_of_struct;
      struct module        *next;
      const char           *name;
      unsigned long         size;
      long                  usecount;
      unsigned long         flags;
      unsigned int          nsyms;
      unsigned int          ndeps;
      struct module_symbol *syms;
      struct module_ref    *deps;
      struct module_ref    *refs;
      int                 (*init)(void);
      void                (*cleanup)(void);
      const struct exception_table_entry *ex_table_start;
      const struct exception_table_entry *ex_table_end;
  #ifdef __alpha__
      unsigned long gp;
  #endif
  };

All of the pointer fields, with the exception of next and refs, are expected to point within the module body and be initialized as appropriate for kernel space, that is, relocated with the rest of the module.

*create_module*(2), *delete_module*(2), *query_module*(2), *lsmod*(8), *modprobe*(8)

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