delete_module(2) System Calls Manual delete_module(2)
NAME
delete_module - unload a kernel module
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <fcntl.h> /* Definition of O_* constants */
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <unistd.h>
int syscall(SYS_delete_module, const char *name, unsigned int flags);
Note: glibc provides no wrapper for delete_module(), necessitating the
use of syscall(2).
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 de-
scribed 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 de-
pends on the bits set in flags. In normal usage (see NOTES), the
O_NONBLOCK flag is always specified, and the O_TRUNC flag may ad-
ditionally 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_UNIN-
TERRUPTIBLE) 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 to indicate the error.
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 ad-
dress 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.
STANDARDS
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 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 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 op-
tional, 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), mod-
probe(8), rmmod(8)
Linux man-pages 6.03 2023-02-05 delete_module(2)
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