DELETE_MODULE(2)                                                        Linux Programmer's Manual                                                       DELETE_MODULE(2)

NAME
       delete_module - unload a kernel module

SYNOPSIS
       #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).

DESCRIPTION
       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 behavior 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_UNINTERRUPTIBLE) 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 re‐
       move 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  ignored.   (Normally,  CONFIG_MOD‐
       ULE_FORCE_UNLOAD is enabled.)  Using this flag taints the kernel (TAINT_FORCED_RMMOD).

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

ERRORS
       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 func‐
              tion, 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)).

       EWOULDBLOCK
              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 speci‐
              fied in flags.

CONFORMING TO
       delete_module() is Linux-specific.

NOTES
       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
       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 inter‐
       face 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.

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

Linux                                                                          2021-03-22                                                               DELETE_MODULE(2)