man2/delete_module.2

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  25 .TH DELETE_MODULE 2 2017-09-15 "Linux" "Linux Programmer's Manual"
  26 .SH NAME
  27 delete_module \- unload a kernel module
  28 .SH SYNOPSIS
  29 .nf
  30 .BI "int delete_module(const char *" name ", int " flags );
  31 .fi
  32 .PP
  33 .IR Note :
  34 No declaration of this system call is provided in glibc headers; see NOTES.
  35 .SH DESCRIPTION
  36 The
  37 .BR delete_module ()
  38 system call attempts to remove the unused loadable module entry
  39 identified by
  40 .IR name .
  41 If the module has an
  42 .I exit
  43 function, then that function is executed before unloading the module.
  44 The
  45 .IR flags
  46 argument is used to modify the behavior of the system call,
  47 as described below.
  48 This system call requires privilege.
  49 .PP
  50 Module removal is attempted according to the following rules:
  51 .IP 1. 4
  52 If there are other loaded modules that depend on
  53 (i.e., refer to symbols defined in) this module,
  54 then the call fails.
  55 .IP 2.
  56 Otherwise, if the reference count for the module
  57 (i.e., the number of processes currently using the module)
  58 is zero, then the module is immediately unloaded.
  59 .IP 3.
  60 If a module has a nonzero reference count,
  61 then the behavior depends on the bits set in
  62 .IR flags .
  63 In normal usage (see NOTES), the
  64 .BR O_NONBLOCK
  65 flag is always specified, and the
  66 .BR O_TRUNC
  67 flag may additionally be specified.
  68 .\"     O_TRUNC == KMOD_REMOVE_FORCE in kmod library
  69 .\"     O_NONBLOCK == KMOD_REMOVE_NOWAIT in kmod library
  70 .IP
  71 The various combinations for
  72 .I flags
  73 have the following effect:
  74 .RS 4
  75 .TP
  76 .B flags == O_NONBLOCK
  77 The call returns immediately, with an error.
  78 .TP
  79 .B flags == (O_NONBLOCK | O_TRUNC)
  80 The module is unloaded immediately,
  81 regardless of whether it has a nonzero reference count.
  82 .TP
  83 .B (flags & O_NONBLOCK) == 0
  84 If
  85 .I flags
  86 does not specify
  87 .BR O_NONBLOCK ,
  88 the following steps occur:
  89 .RS
  90 .IP * 3
  91 The module is marked so that no new references are permitted.
  92 .IP *
  93 If the module's reference count is nonzero,
  94 the caller is placed in an uninterruptible sleep state
  95 .RB ( TASK_UNINTERRUPTIBLE )
  96 until the reference count is zero, at which point the call unblocks.
  97 .IP *
  98 The module is unloaded in the usual way.
  99 .RE
 100 .RE
 101 .PP
 102 The
 103 .B O_TRUNC
 104 flag has one further effect on the rules described above.
 105 By default, if a module has an
 106 .I init
 107 function but no
 108 .I exit
 109 function, then an attempt to remove the module fails.
 110 However, if
 111 .BR O_TRUNC
 112 was specified, this requirement is bypassed.
 113 .PP
 114 Using the
 115 .B O_TRUNC
 116 flag is dangerous!
 117 If the kernel was not built with
 118 .BR CONFIG_MODULE_FORCE_UNLOAD ,
 119 this flag is silently ignored.
 120 (Normally,
 121 .BR CONFIG_MODULE_FORCE_UNLOAD
 122 is enabled.)
 123 Using this flag taints the kernel (TAINT_FORCED_RMMOD).
 124 .SH RETURN VALUE
 125 On success, zero is returned.
 126 On error, \-1 is returned and
 127 .I errno
 128 is set appropriately.
 129 .SH ERRORS
 130 .TP
 131 .B EBUSY
 132 The module is not "live"
 133 (i.e., it is still being initialized or is already marked for removal);
 134 or, the module has
 135 an
 136 .I init
 137 function but has no
 138 .I exit
 139 function, and
 140 .B O_TRUNC
 141 was not specified in
 142 .IR flags .
 143 .TP
 144 .B EFAULT
 145 .I name
 146 refers to a location outside the process's accessible address space.
 147 .TP
 148 .B ENOENT
 149 No module by that name exists.
 150 .TP
 151 .B EPERM
 152 The caller was not privileged
 153 (did not have the
 154 .B CAP_SYS_MODULE
 155 capability),
 156 or module unloading is disabled
 157 (see
 158 .IR /proc/sys/kernel/modules_disabled
 159 in
 160 .BR proc (5)).
 161 .TP
 162 .B EWOULDBLOCK
 163 Other modules depend on this module;
 164 or,
 165 .BR O_NONBLOCK
 166 was specified in
 167 .IR flags ,
 168 but the reference count of this module is nonzero and
 169 .B O_TRUNC
 170 was not specified in
 171 .IR flags .
 172 .SH CONFORMING TO
 173 .BR delete_module ()
 174 is Linux-specific.
 175 .SH NOTES
 176 The
 177 .BR delete_module ()
 178 system call is not supported by glibc.
 179 No declaration is provided in glibc headers, but, through a quirk of history,
 180 glibc versions before 2.23 did export an ABI for this system call.
 181 Therefore, in order to employ this system call,
 182 it is (before glibc 2.23) sufficient to
 183 manually declare the interface in your code;
 184 alternatively, you can invoke the system call using
 185 .BR syscall (2).
 186 .PP
 187 The uninterruptible sleep that may occur if
 188 .BR O_NONBLOCK
 189 is omitted from
 190 .IR flags
 191 is considered undesirable, because the sleeping process is left
 192 in an unkillable state.
 193 As at Linux 3.7, specifying
 194 .BR O_NONBLOCK
 195 is optional, but in future kernels it is likely to become mandatory.
 196 .SS Linux 2.4 and earlier
 197 In Linux 2.4 and earlier, the system call took only one argument:
 198 .PP
 199 .BI "   int delete_module(const char *" name );
 200 .PP
 201 If
 202 .I name
 203 is NULL, all unused modules marked auto-clean are removed.
 204 .PP
 205 Some further details of differences in the behavior of
 206 .BR delete_module ()
 207 in Linux 2.4 and earlier are
 208 .I not
 209 currently explained in this manual page.
 210 .SH SEE ALSO
 211 .BR create_module (2),
 212 .BR init_module (2),
 213 .BR query_module (2),
 214 .BR lsmod (8),
 215 .BR modprobe (8),
 216 .BR rmmod (8)