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Documentation: kernel-hacking: Remove :c:func: annotations 

Remove the useless :c:func: annotations.

Suggested-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20251222232506.2615-2-thorsten.blum@linux.dev>
master
Thorsten Blum 2025-12-23 00:25:04 +01:00 committed by Jonathan Corbet
parent bb51cf4f61
commit 736ea81026
1 changed files with 84 additions and 85 deletions
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169
Documentation/kernel-hacking/hacking.rst
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@ -49,7 +49,7 @@ User Context
User context is when you are coming in from a system call or other trap:
like userspace, you can be preempted by more important tasks and by
interrupts. You can sleep by calling :c:func:`schedule()`.
interrupts. You can sleep by calling schedule().
.. note::
@ -57,13 +57,13 @@ interrupts. You can sleep by calling :c:func:`schedule()`.
operations on the block device layer.
In user context, the ``current`` pointer (indicating the task we are
currently executing) is valid, and :c:func:`in_interrupt()`
currently executing) is valid, and in_interrupt()
(``include/linux/preempt.h``) is false.
.. warning::
Beware that if you have preemption or softirqs disabled (see below),
:c:func:`in_interrupt()` will return a false positive.
in_interrupt() will return a false positive.
Hardware Interrupts (Hard IRQs)
-------------------------------
@ -115,7 +115,7 @@ time, although different tasklets can run simultaneously.
'tasks'.
You can tell you are in a softirq (or tasklet) using the
:c:func:`in_softirq()` macro (``include/linux/preempt.h``).
in_softirq() macro (``include/linux/preempt.h``).
.. warning::
@ -171,7 +171,7 @@ in every architecture's ``include/asm/unistd.h`` and
Linus.
If all your routine does is read or write some parameter, consider
implementing a :c:func:`sysfs()` interface instead.
implementing a sysfs() interface instead.
Inside the ioctl you're in user context to a process. When a error
occurs you return a negated errno (see
@ -230,12 +230,12 @@ Really.
Common Routines
===============
:c:func:`printk()`
------------------
printk()
--------
Defined in ``include/linux/printk.h``
:c:func:`printk()` feeds kernel messages to the console, dmesg, and
printk() feeds kernel messages to the console, dmesg, and
the syslog daemon. It is useful for debugging and reporting errors, and
can be used inside interrupt context, but use with caution: a machine
which has its console flooded with printk messages is unusable. It uses
@ -253,7 +253,7 @@ address use::
printk(KERN_INFO "my ip: %pI4\n", &ipaddress);
:c:func:`printk()` internally uses a 1K buffer and does not catch
printk() internally uses a 1K buffer and does not catch
overruns. Make sure that will be enough.
.. note::
@ -267,26 +267,26 @@ overruns. Make sure that will be enough.
on top of its printf function: "Printf should not be used for
chit-chat". You should follow that advice.
:c:func:`copy_to_user()` / :c:func:`copy_from_user()` / :c:func:`get_user()` / :c:func:`put_user()`
---------------------------------------------------------------------------------------------------
copy_to_user() / copy_from_user() / get_user() / put_user()
-----------------------------------------------------------
Defined in ``include/linux/uaccess.h`` / ``asm/uaccess.h``
**[SLEEPS]**
:c:func:`put_user()` and :c:func:`get_user()` are used to get
put_user() and get_user() are used to get
and put single values (such as an int, char, or long) from and to
userspace. A pointer into userspace should never be simply dereferenced:
data should be copied using these routines. Both return ``-EFAULT`` or
0.
:c:func:`copy_to_user()` and :c:func:`copy_from_user()` are
copy_to_user() and copy_from_user() are
more general: they copy an arbitrary amount of data to and from
userspace.
.. warning::
Unlike :c:func:`put_user()` and :c:func:`get_user()`, they
Unlike put_user() and get_user(), they
return the amount of uncopied data (ie. 0 still means success).
[Yes, this objectionable interface makes me cringe. The flamewar comes
@ -296,8 +296,8 @@ The functions may sleep implicitly. This should never be called outside
user context (it makes no sense), with interrupts disabled, or a
spinlock held.
:c:func:`kmalloc()`/:c:func:`kfree()`
-------------------------------------
kmalloc()/kfree()
-----------------
Defined in ``include/linux/slab.h``
@ -305,7 +305,7 @@ Defined in ``include/linux/slab.h``
These routines are used to dynamically request pointer-aligned chunks of
memory, like malloc and free do in userspace, but
:c:func:`kmalloc()` takes an extra flag word. Important values:
kmalloc() takes an extra flag word. Important values:
``GFP_KERNEL``
May sleep and swap to free memory. Only allowed in user context, but
@ -326,20 +326,20 @@ interrupt context without ``GFP_ATOMIC``. You should really fix that.
Run, don't walk.
If you are allocating at least ``PAGE_SIZE`` (``asm/page.h`` or
``asm/page_types.h``) bytes, consider using :c:func:`__get_free_pages()`
``asm/page_types.h``) bytes, consider using __get_free_pages()
(``include/linux/gfp.h``). It takes an order argument (0 for page sized,
1 for double page, 2 for four pages etc.) and the same memory priority
flag word as above.
If you are allocating more than a page worth of bytes you can use
:c:func:`vmalloc()`. It'll allocate virtual memory in the kernel
vmalloc(). It'll allocate virtual memory in the kernel
map. This block is not contiguous in physical memory, but the MMU makes
it look like it is for you (so it'll only look contiguous to the CPUs,
not to external device drivers). If you really need large physically
contiguous memory for some weird device, you have a problem: it is
poorly supported in Linux because after some time memory fragmentation
in a running kernel makes it hard. The best way is to allocate the block
early in the boot process via the :c:func:`alloc_bootmem()`
early in the boot process via the alloc_bootmem()
routine.
Before inventing your own cache of often-used objects consider using a
@ -355,48 +355,48 @@ task structure, so is only valid in user context. For example, when a
process makes a system call, this will point to the task structure of
the calling process. It is **not NULL** in interrupt context.
:c:func:`mdelay()`/:c:func:`udelay()`
-------------------------------------
mdelay()/udelay()
-----------------
Defined in ``include/asm/delay.h`` / ``include/linux/delay.h``
The :c:func:`udelay()` and :c:func:`ndelay()` functions can be
The udelay() and ndelay() functions can be
used for small pauses. Do not use large values with them as you risk
overflow - the helper function :c:func:`mdelay()` is useful here, or
consider :c:func:`msleep()`.
overflow - the helper function mdelay() is useful here, or
consider msleep().
:c:func:`cpu_to_be32()`/:c:func:`be32_to_cpu()`/:c:func:`cpu_to_le32()`/:c:func:`le32_to_cpu()`
-----------------------------------------------------------------------------------------------
cpu_to_be32()/be32_to_cpu()/cpu_to_le32()/le32_to_cpu()
-------------------------------------------------------
Defined in ``include/asm/byteorder.h``
The :c:func:`cpu_to_be32()` family (where the "32" can be replaced
The cpu_to_be32() family (where the "32" can be replaced
by 64 or 16, and the "be" can be replaced by "le") are the general way
to do endian conversions in the kernel: they return the converted value.
All variations supply the reverse as well:
:c:func:`be32_to_cpu()`, etc.
be32_to_cpu(), etc.
There are two major variations of these functions: the pointer
variation, such as :c:func:`cpu_to_be32p()`, which take a pointer
variation, such as cpu_to_be32p(), which take a pointer
to the given type, and return the converted value. The other variation
is the "in-situ" family, such as :c:func:`cpu_to_be32s()`, which
is the "in-situ" family, such as cpu_to_be32s(), which
convert value referred to by the pointer, and return void.
:c:func:`local_irq_save()`/:c:func:`local_irq_restore()`
--------------------------------------------------------
local_irq_save()/local_irq_restore()
------------------------------------
Defined in ``include/linux/irqflags.h``
These routines disable hard interrupts on the local CPU, and restore
them. They are reentrant; saving the previous state in their one
``unsigned long flags`` argument. If you know that interrupts are
enabled, you can simply use :c:func:`local_irq_disable()` and
:c:func:`local_irq_enable()`.
enabled, you can simply use local_irq_disable() and
local_irq_enable().
.. _local_bh_disable:
:c:func:`local_bh_disable()`/:c:func:`local_bh_enable()`
--------------------------------------------------------
local_bh_disable()/local_bh_enable()
------------------------------------
Defined in ``include/linux/bottom_half.h``
@ -406,15 +406,15 @@ them. They are reentrant; if soft interrupts were disabled before, they
will still be disabled after this pair of functions has been called.
They prevent softirqs and tasklets from running on the current CPU.
:c:func:`smp_processor_id()`
----------------------------
smp_processor_id()
------------------
Defined in ``include/linux/smp.h``
:c:func:`get_cpu()` disables preemption (so you won't suddenly get
get_cpu() disables preemption (so you won't suddenly get
moved to another CPU) and returns the current processor number, between
0 and ``NR_CPUS``. Note that the CPU numbers are not necessarily
continuous. You return it again with :c:func:`put_cpu()` when you
continuous. You return it again with put_cpu() when you
are done.
If you know you cannot be preempted by another task (ie. you are in
@ -433,25 +433,25 @@ initialization. ``__exit`` is used to declare a function which is only
required on exit: the function will be dropped if this file is not
compiled as a module. See the header file for use. Note that it makes no
sense for a function marked with ``__init`` to be exported to modules
with :c:func:`EXPORT_SYMBOL()` or :c:func:`EXPORT_SYMBOL_GPL()`- this
with EXPORT_SYMBOL() or EXPORT_SYMBOL_GPL()- this
will break.
:c:func:`__initcall()`/:c:func:`module_init()`
----------------------------------------------
__initcall()/module_init()
--------------------------
Defined in ``include/linux/init.h`` / ``include/linux/module.h``
Many parts of the kernel are well served as a module
(dynamically-loadable parts of the kernel). Using the
:c:func:`module_init()` and :c:func:`module_exit()` macros it
module_init() and module_exit() macros it
is easy to write code without #ifdefs which can operate both as a module
or built into the kernel.
The :c:func:`module_init()` macro defines which function is to be
The module_init() macro defines which function is to be
called at module insertion time (if the file is compiled as a module),
or at boot time: if the file is not compiled as a module the
:c:func:`module_init()` macro becomes equivalent to
:c:func:`__initcall()`, which through linker magic ensures that
module_init() macro becomes equivalent to
__initcall(), which through linker magic ensures that
the function is called on boot.
The function can return a negative error number to cause module loading
@ -459,9 +459,8 @@ to fail (unfortunately, this has no effect if the module is compiled
into the kernel). This function is called in user context with
interrupts enabled, so it can sleep.
:c:func:`module_exit()`
-----------------------
module_exit()
-------------
Defined in ``include/linux/module.h``
@ -474,18 +473,18 @@ it returns.
Note that this macro is optional: if it is not present, your module will
not be removable (except for 'rmmod -f').
:c:func:`try_module_get()`/:c:func:`module_put()`
-------------------------------------------------
try_module_get()/module_put()
-----------------------------
Defined in ``include/linux/module.h``
These manipulate the module usage count, to protect against removal (a
module also can't be removed if another module uses one of its exported
symbols: see below). Before calling into module code, you should call
:c:func:`try_module_get()` on that module: if it fails, then the
try_module_get() on that module: if it fails, then the
module is being removed and you should act as if it wasn't there.
Otherwise, you can safely enter the module, and call
:c:func:`module_put()` when you're finished.
module_put() when you're finished.
Most registerable structures have an owner field, such as in the
:c:type:`struct file_operations <file_operations>` structure.
@ -506,8 +505,8 @@ Declaring
---------
You declare a ``wait_queue_head_t`` using the
:c:func:`DECLARE_WAIT_QUEUE_HEAD()` macro, or using the
:c:func:`init_waitqueue_head()` routine in your initialization
DECLARE_WAIT_QUEUE_HEAD() macro, or using the
init_waitqueue_head() routine in your initialization
code.
Queuing
@ -515,16 +514,16 @@ Queuing
Placing yourself in the waitqueue is fairly complex, because you must
put yourself in the queue before checking the condition. There is a
macro to do this: :c:func:`wait_event_interruptible()`
macro to do this: wait_event_interruptible()
(``include/linux/wait.h``) The first argument is the wait queue head, and
the second is an expression which is evaluated; the macro returns 0 when
this expression is true, or ``-ERESTARTSYS`` if a signal is received. The
:c:func:`wait_event()` version ignores signals.
wait_event() version ignores signals.
Waking Up Queued Tasks
----------------------
Call :c:func:`wake_up()` (``include/linux/wait.h``), which will wake
Call wake_up() (``include/linux/wait.h``), which will wake
up every process in the queue. The exception is if one has
``TASK_EXCLUSIVE`` set, in which case the remainder of the queue will
not be woken. There are other variants of this basic function available
@ -537,10 +536,10 @@ Certain operations are guaranteed atomic on all platforms. The first
class of operations work on :c:type:`atomic_t` (``include/asm/atomic.h``);
this contains a signed integer (at least 32 bits long), and you must use
these functions to manipulate or read :c:type:`atomic_t` variables.
:c:func:`atomic_read()` and :c:func:`atomic_set()` get and set
the counter, :c:func:`atomic_add()`, :c:func:`atomic_sub()`,
:c:func:`atomic_inc()`, :c:func:`atomic_dec()`, and
:c:func:`atomic_dec_and_test()` (returns true if it was
atomic_read() and atomic_set() get and set
the counter, atomic_add(), atomic_sub(),
atomic_inc(), atomic_dec(), and
atomic_dec_and_test() (returns true if it was
decremented to zero).
Yes. It returns true (i.e. != 0) if the atomic variable is zero.
@ -551,11 +550,11 @@ should not be used unnecessarily.
The second class of atomic operations is atomic bit operations on an
``unsigned long``, defined in ``include/linux/bitops.h``. These
operations generally take a pointer to the bit pattern, and a bit
number: 0 is the least significant bit. :c:func:`set_bit()`,
:c:func:`clear_bit()` and :c:func:`change_bit()` set, clear,
and flip the given bit. :c:func:`test_and_set_bit()`,
:c:func:`test_and_clear_bit()` and
:c:func:`test_and_change_bit()` do the same thing, except return
number: 0 is the least significant bit. set_bit(),
clear_bit() and change_bit() set, clear,
and flip the given bit. test_and_set_bit(),
test_and_clear_bit() and
test_and_change_bit() do the same thing, except return
true if the bit was previously set; these are particularly useful for
atomically setting flags.
@ -572,29 +571,29 @@ be used anywhere in the kernel). However, for modules, a special
exported symbol table is kept which limits the entry points to the
kernel proper. Modules can also export symbols.
:c:func:`EXPORT_SYMBOL()`
-------------------------
EXPORT_SYMBOL()
---------------
Defined in ``include/linux/export.h``
This is the classic method of exporting a symbol: dynamically loaded
modules will be able to use the symbol as normal.
:c:func:`EXPORT_SYMBOL_GPL()`
-----------------------------
EXPORT_SYMBOL_GPL()
-------------------
Defined in ``include/linux/export.h``
Similar to :c:func:`EXPORT_SYMBOL()` except that the symbols
exported by :c:func:`EXPORT_SYMBOL_GPL()` can only be seen by
modules with a :c:func:`MODULE_LICENSE()` that specifies a GPLv2
Similar to EXPORT_SYMBOL() except that the symbols
exported by EXPORT_SYMBOL_GPL() can only be seen by
modules with a MODULE_LICENSE() that specifies a GPLv2
compatible license. It implies that the function is considered an
internal implementation issue, and not really an interface. Some
maintainers and developers may however require EXPORT_SYMBOL_GPL()
when adding any new APIs or functionality.
:c:func:`EXPORT_SYMBOL_NS()`
----------------------------
EXPORT_SYMBOL_NS()
------------------
Defined in ``include/linux/export.h``
@ -602,8 +601,8 @@ This is the variant of EXPORT_SYMBOL() that allows specifying a symbol
namespace. Symbol Namespaces are documented in
Documentation/core-api/symbol-namespaces.rst
:c:func:`EXPORT_SYMBOL_NS_GPL()`
--------------------------------
EXPORT_SYMBOL_NS_GPL()
----------------------
Defined in ``include/linux/export.h``
@ -621,7 +620,7 @@ There used to be three sets of linked-list routines in the kernel
headers, but this one is the winner. If you don't have some particular
pressing need for a single list, it's a good choice.
In particular, :c:func:`list_for_each_entry()` is useful.
In particular, list_for_each_entry() is useful.
Return Conventions
------------------
@ -631,9 +630,9 @@ and return 0 for success, and a negative error number (eg. ``-EFAULT``) for
failure. This can be unintuitive at first, but it's fairly widespread in
the kernel.
Using :c:func:`ERR_PTR()` (``include/linux/err.h``) to encode a
negative error number into a pointer, and :c:func:`IS_ERR()` and
:c:func:`PTR_ERR()` to get it back out again: avoids a separate
Using ERR_PTR() (``include/linux/err.h``) to encode a
negative error number into a pointer, and IS_ERR() and
PTR_ERR() to get it back out again: avoids a separate
pointer parameter for the error number. Icky, but in a good way.
Breaking Compilation
@ -824,7 +823,7 @@ Thanks
Thanks to Andi Kleen for the idea, answering my questions, fixing my
mistakes, filling content, etc. Philipp Rumpf for more spelling and
clarity fixes, and some excellent non-obvious points. Werner Almesberger
for giving me a great summary of :c:func:`disable_irq()`, and Jes
for giving me a great summary of disable_irq(), and Jes
Sorensen and Andrea Arcangeli added caveats. Michael Elizabeth Chastain
for checking and adding to the Configure section. Telsa Gwynne for
teaching me DocBook.