bionic (2) delete_module.2.gz

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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
           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 (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 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)).

       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 specified 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 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.

SEE ALSO

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

COLOPHON

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