.\" Copyright (C) 2012 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH delete_module 2 2023-02-05 "Linux man-pages 6.03"
.SH NAME
delete_module \- unload a kernel module
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.BR "#include <fcntl.h>" "            /* Definition of " O_* " constants */"
.BR "#include <sys/syscall.h>" "      /* Definition of " SYS_* " constants */"
.B #include <unistd.h>
.PP
.BI "int syscall(SYS_delete_module, const char *" name ", unsigned int " flags );
.fi
.PP
.IR Note :
glibc provides no wrapper for
.BR delete_module (),
necessitating the use of
.BR syscall (2).
.SH DESCRIPTION
The
.BR delete_module ()
system call attempts to remove the unused loadable module entry
identified by
.IR name .
If the module has an
.I exit
function, then that function is executed before unloading the module.
The
.I flags
argument is used to modify the behavior of the system call,
as described below.
This system call requires privilege.
.PP
Module removal is attempted according to the following rules:
.IP (1) 5
If there are other loaded modules that depend on
(i.e., refer to symbols defined in) this module,
then the call fails.
.IP (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.
.IP (3)
If a module has a nonzero reference count,
then the behavior depends on the bits set in
.IR flags .
In normal usage (see NOTES), the
.B O_NONBLOCK
flag is always specified, and the
.B O_TRUNC
flag may additionally be specified.
.\"  	O_TRUNC == KMOD_REMOVE_FORCE in kmod library
.\"  	O_NONBLOCK == KMOD_REMOVE_NOWAIT in kmod library
.IP
The various combinations for
.I flags
have the following effect:
.RS
.TP
.B flags == O_NONBLOCK
The call returns immediately, with an error.
.TP
.B flags == (O_NONBLOCK | O_TRUNC)
The module is unloaded immediately,
regardless of whether it has a nonzero reference count.
.TP
.B (flags & O_NONBLOCK) == 0
If
.I flags
does not specify
.BR O_NONBLOCK ,
the following steps occur:
.RS
.IP \[bu] 3
The module is marked so that no new references are permitted.
.IP \[bu]
If the module's reference count is nonzero,
the caller is placed in an uninterruptible sleep state
.RB ( TASK_UNINTERRUPTIBLE )
until the reference count is zero, at which point the call unblocks.
.IP \[bu]
The module is unloaded in the usual way.
.RE
.RE
.PP
The
.B O_TRUNC
flag has one further effect on the rules described above.
By default, if a module has an
.I init
function but no
.I exit
function, then an attempt to remove the module fails.
However, if
.B O_TRUNC
was specified, this requirement is bypassed.
.PP
Using the
.B O_TRUNC
flag is dangerous!
If the kernel was not built with
.BR CONFIG_MODULE_FORCE_UNLOAD ,
this flag is silently ignored.
(Normally,
.B CONFIG_MODULE_FORCE_UNLOAD
is enabled.)
Using this flag taints the kernel (TAINT_FORCED_RMMOD).
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EBUSY
The module is not "live"
(i.e., it is still being initialized or is already marked for removal);
or, the module has
an
.I init
function but has no
.I exit
function, and
.B O_TRUNC
was not specified in
.IR flags .
.TP
.B EFAULT
.I name
refers to a location outside the process's accessible address space.
.TP
.B ENOENT
No module by that name exists.
.TP
.B EPERM
The caller was not privileged
(did not have the
.B CAP_SYS_MODULE
capability),
or module unloading is disabled
(see
.I /proc/sys/kernel/modules_disabled
in
.BR proc (5)).
.TP
.B EWOULDBLOCK
Other modules depend on this module;
or,
.B O_NONBLOCK
was specified in
.IR flags ,
but the reference count of this module is nonzero and
.B O_TRUNC
was not specified in
.IR flags .
.SH STANDARDS
.BR delete_module ()
is Linux-specific.
.SH NOTES
The
.BR 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
.BR syscall (2).
.PP
The uninterruptible sleep that may occur if
.B O_NONBLOCK
is omitted from
.I flags
is considered undesirable, because the sleeping process is left
in an unkillable state.
As at Linux 3.7, specifying
.B O_NONBLOCK
is optional, but in future kernels it is likely to become mandatory.
.SS Linux 2.4 and earlier
In Linux 2.4 and earlier, the system call took only one argument:
.PP
.BI "   int delete_module(const char *" name );
.PP
If
.I name
is NULL, all unused modules marked auto-clean are removed.
.PP
Some further details of differences in the behavior of
.BR delete_module ()
in Linux 2.4 and earlier are
.I not
currently explained in this manual page.
.SH SEE ALSO
.BR create_module (2),
.BR init_module (2),
.BR query_module (2),
.BR lsmod (8),
.BR modprobe (8),
.BR rmmod (8)