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       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 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  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     ignored.      (Normally,
       CONFIG_MODULE_FORCE_UNLOAD   is   enabled.)    Using   this   flag   taints   the   kernel


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


       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

   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)