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

NAME

     delete_module - unload a kernel module

SYNOPSIS

     int delete_module(const char *name, int flags);

     Note:  No declaration of this system call is provided in glibc headers;
     see NOTES.

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 addi-
         tionally 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 per-

mitted.

If the module's reference count is nonzero, the caller is

placed in an uninterruptible sleep state (TASK_UNINTER-

                   RUPTIBLE)  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  speci-
     fied, 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 (TAINT_FORCED_RMMOD).

RETURN VALUE

     On success, zero is returned.  On error, -1 is returned  and  errno  is
     set appropriately.

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 func-
            tion  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/ker-
            nel/modules_disabled in proc(5)).

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

CONFORMING TO

     delete_module() is Linux-specific.

NOTES

     The delete_module() system call is not supported by glibc.  No declara-
     tion 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; alter-
     natively, 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.