delete_module(2)                                        System Calls Manual                                        delete_module(2)

       delete_module - unload a kernel module

       Standard C library (libc, -lc)

       #include <fcntl.h>            /* Definition of O_* constants */
       #include <sys/syscall.h>      /* Definition of SYS_* constants */
       #include <unistd.h>

       int syscall(SYS_delete_module, const char *name, unsigned int flags);

       Note: glibc provides no wrapper for delete_module(), necessitating the use of syscall(2).

       The  delete_module()  system call attempts to remove the unused loadable module entry identified by name.  If the module has
       an exit function, then that function is executed before unloading the module.  The flags argument is used to modify the  be‐
       havior of the system call, as described below.  This system call requires privilege.

       Module removal is attempted according to the following rules:

       (1)  If there are other loaded modules that depend on (i.e., refer to symbols defined in) this module, then the call fails.

       (2)  Otherwise,  if  the  reference count for the module (i.e., the number of processes currently using the module) is zero,
            then the module is immediately unloaded.

       (3)  If a module has a nonzero reference count, then the behavior depends on the bits set in flags.  In  normal  usage  (see
            NOTES), the O_NONBLOCK flag is always specified, and the O_TRUNC flag may additionally be specified.

            The various combinations for flags have the following effect:

            flags == O_NONBLOCK
                   The call returns immediately, with an error.

            flags == (O_NONBLOCK | O_TRUNC)
                   The module is unloaded immediately, regardless of whether it has a nonzero reference count.

            (flags & O_NONBLOCK) == 0
                   If flags does not specify O_NONBLOCK, the following steps occur:

                   •  The module is marked so that no new references are permitted.

                   •  If  the module's reference count is nonzero, the caller is placed in an uninterruptible sleep state (TASK_UN‐
                      INTERRUPTIBLE) until the reference count is zero, at which point the call unblocks.

                   •  The module is unloaded in the usual way.

       The O_TRUNC flag has one further effect on the rules described above.  By default, if a module has an init function  but  no
       exit function, then an attempt to remove the module fails.  However, if O_TRUNC was specified, this requirement is bypassed.

       Using the O_TRUNC flag is dangerous!  If the kernel was not built with CONFIG_MODULE_FORCE_UNLOAD, this flag is silently ig‐
       nored.  (Normally, CONFIG_MODULE_FORCE_UNLOAD is enabled.)  Using this flag taints the kernel (TAINT_FORCED_RMMOD).

       On success, zero is returned.  On error, -1 is returned and errno is set to indicate the error.

       EBUSY  The module is not "live" (i.e., it is still being initialized or is already marked for removal); or, the  module  has
              an init function but has no exit function, and O_TRUNC was not specified in flags.

       EFAULT name refers to a location outside the process's accessible address space.

       ENOENT No module by that name exists.

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

              Other modules depend on this module; or, O_NONBLOCK was specified in flags, but the reference count of this module is
              nonzero and O_TRUNC was not specified in flags.

       delete_module() is Linux-specific.

       The  delete_module()  system  call  is  not supported by glibc.  No declaration is provided in glibc headers, but, through a
       quirk of history, glibc versions before glibc 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).

       The uninterruptible sleep that may occur if O_NONBLOCK is omitted from flags is considered undesirable, because the sleeping
       process  is  left  in  an unkillable state.  As at Linux 3.7, specifying O_NONBLOCK is optional, but in future kernels it is
       likely to become mandatory.

   Linux 2.4 and earlier
       In Linux 2.4 and earlier, the system call took only one argument:

          int delete_module(const char *name);

       If name is NULL, all unused modules marked auto-clean are removed.

       Some further details of differences in the behavior of delete_module() in Linux 2.4 and earlier are not currently  explained
       in this manual page.

       create_module(2), init_module(2), query_module(2), lsmod(8), modprobe(8), rmmod(8)

Linux man-pages 6.03                                         2023-02-05                                            delete_module(2)