mirror of https://github.com/mkerrisk/man-pages
218 lines
5.9 KiB
Groff
218 lines
5.9 KiB
Groff
.\" Copyright (C) 2012 Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.TH DELETE_MODULE 2 2021-03-22 "Linux" "Linux Programmer's Manual"
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.SH NAME
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delete_module \- unload a kernel module
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.SH SYNOPSIS
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.nf
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.BR "#include <fcntl.h>" " /* Definition of " O_* " constants */"
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.BR "#include <sys/syscall.h>" " /* Definition of " SYS_* " constants */"
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.BR "#include <unistd.h>
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.PP
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.BI "int syscall(SYS_delete_module, const char *" name ", unsigned int " flags );
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.fi
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.SH DESCRIPTION
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The
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.BR delete_module ()
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system call attempts to remove the unused loadable module entry
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identified by
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.IR name .
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If the module has an
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.I exit
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function, then that function is executed before unloading the module.
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The
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.IR flags
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argument is used to modify the behavior of the system call,
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as described below.
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This system call requires privilege.
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.PP
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Module removal is attempted according to the following rules:
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.IP 1. 4
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If there are other loaded modules that depend on
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(i.e., refer to symbols defined in) this module,
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then the call fails.
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.IP 2.
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Otherwise, if the reference count for the module
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(i.e., the number of processes currently using the module)
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is zero, then the module is immediately unloaded.
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.IP 3.
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If a module has a nonzero reference count,
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then the behavior depends on the bits set in
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.IR flags .
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In normal usage (see NOTES), the
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.BR O_NONBLOCK
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flag is always specified, and the
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.BR O_TRUNC
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flag may additionally be specified.
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.\" O_TRUNC == KMOD_REMOVE_FORCE in kmod library
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.\" O_NONBLOCK == KMOD_REMOVE_NOWAIT in kmod library
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.IP
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The various combinations for
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.I flags
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have the following effect:
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.RS 4
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.TP
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.B flags == O_NONBLOCK
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The call returns immediately, with an error.
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.TP
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.B flags == (O_NONBLOCK | O_TRUNC)
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The module is unloaded immediately,
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regardless of whether it has a nonzero reference count.
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.TP
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.B (flags & O_NONBLOCK) == 0
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If
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.I flags
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does not specify
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.BR O_NONBLOCK ,
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the following steps occur:
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.RS
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.IP * 3
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The module is marked so that no new references are permitted.
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.IP *
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If the module's reference count is nonzero,
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the caller is placed in an uninterruptible sleep state
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.RB ( TASK_UNINTERRUPTIBLE )
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until the reference count is zero, at which point the call unblocks.
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.IP *
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The module is unloaded in the usual way.
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.RE
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.RE
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.PP
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The
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.B O_TRUNC
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flag has one further effect on the rules described above.
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By default, if a module has an
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.I init
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function but no
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.I exit
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function, then an attempt to remove the module fails.
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However, if
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.BR O_TRUNC
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was specified, this requirement is bypassed.
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.PP
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Using the
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.B O_TRUNC
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flag is dangerous!
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If the kernel was not built with
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.BR CONFIG_MODULE_FORCE_UNLOAD ,
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this flag is silently ignored.
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(Normally,
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.BR CONFIG_MODULE_FORCE_UNLOAD
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is enabled.)
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Using this flag taints the kernel (TAINT_FORCED_RMMOD).
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.SH RETURN VALUE
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On success, zero is returned.
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On error, \-1 is returned and
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.I errno
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is set to indicate the error.
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.SH ERRORS
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.TP
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.B EBUSY
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The module is not "live"
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(i.e., it is still being initialized or is already marked for removal);
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or, the module has
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an
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.I init
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function but has no
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.I exit
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function, and
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.B O_TRUNC
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was not specified in
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.IR flags .
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.TP
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.B EFAULT
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.I name
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refers to a location outside the process's accessible address space.
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.TP
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.B ENOENT
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No module by that name exists.
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.TP
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.B EPERM
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The caller was not privileged
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(did not have the
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.B CAP_SYS_MODULE
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capability),
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or module unloading is disabled
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(see
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.IR /proc/sys/kernel/modules_disabled
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in
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.BR proc (5)).
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.TP
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.B EWOULDBLOCK
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Other modules depend on this module;
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or,
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.BR O_NONBLOCK
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was specified in
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.IR flags ,
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but the reference count of this module is nonzero and
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.B O_TRUNC
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was not specified in
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.IR flags .
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.SH CONFORMING TO
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.BR delete_module ()
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is Linux-specific.
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.SH NOTES
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The
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.BR delete_module ()
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system call is not supported by glibc.
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No declaration is provided in glibc headers, but, through a quirk of history,
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glibc versions before 2.23 did export an ABI for this system call.
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Therefore, in order to employ this system call,
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it is (before glibc 2.23) sufficient to
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manually declare the interface in your code;
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alternatively, you can invoke the system call using
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.BR syscall (2).
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.PP
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The uninterruptible sleep that may occur if
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.BR O_NONBLOCK
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is omitted from
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.IR flags
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is considered undesirable, because the sleeping process is left
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in an unkillable state.
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As at Linux 3.7, specifying
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.BR O_NONBLOCK
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is optional, but in future kernels it is likely to become mandatory.
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.SS Linux 2.4 and earlier
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In Linux 2.4 and earlier, the system call took only one argument:
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.PP
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.BI " int delete_module(const char *" name );
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.PP
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If
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.I name
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is NULL, all unused modules marked auto-clean are removed.
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.PP
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Some further details of differences in the behavior of
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.BR delete_module ()
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in Linux 2.4 and earlier are
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.I not
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currently explained in this manual page.
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.SH SEE ALSO
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.BR create_module (2),
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.BR init_module (2),
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.BR query_module (2),
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.BR lsmod (8),
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.BR modprobe (8),
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.BR rmmod (8)
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