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authorLinus Torvalds <torvalds@linux-foundation.org>2018-08-15 00:29:31 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2018-08-15 00:29:31 +0300
commite6ecec342fefc2df01438cb0b8bacdd8641a6418 (patch)
tree44de6f64588253a2787390cb14ab78a6f5992813 /Documentation/core-api
parent747f62305dfb8a592835c7401069bfdbc06acbae (diff)
parent3d83d3188460bf97afa0ac9895265422411e473a (diff)
downloadlinux-e6ecec342fefc2df01438cb0b8bacdd8641a6418.tar.xz
Merge tag 'docs-4.19' of git://git.lwn.net/linux
Pull documentation update from Jonathan Corbet: "This was a moderately busy cycle for docs, with the usual collection of small fixes and updates. We also have new ktime_get_*() docs from Arnd, some kernel-doc fixes, a new set of Italian translations (non so se vale la pena, ma non fa male - speriamo bene), and some extensive early memory-management documentation improvements from Mike Rapoport" * tag 'docs-4.19' of git://git.lwn.net/linux: (52 commits) Documentation: corrections to console/console.txt Documentation: add ioctl number entry for v4l2-subdev.h Remove gendered language from management style documentation scripts/kernel-doc: Escape all literal braces in regexes docs/mm: add description of boot time memory management docs/mm: memblock: add overview documentation docs/mm: memblock: add kernel-doc description for memblock types docs/mm: memblock: add kernel-doc comments for memblock_add[_node] docs/mm: memblock: update kernel-doc comments mm/memblock: add a name for memblock flags enumeration docs/mm: bootmem: add overview documentation docs/mm: bootmem: add kernel-doc description of 'struct bootmem_data' docs/mm: bootmem: fix kernel-doc warnings docs/mm: nobootmem: fixup kernel-doc comments mm/bootmem: drop duplicated kernel-doc comments Documentation: vm.txt: Adding 'nr_hugepages_mempolicy' parameter description. doc:it_IT: translation for kernel-hacking docs: Fix the reference labels in Locking.rst doc: tracing: Fix a typo of trace_stat mm: Introduce new type vm_fault_t ...
Diffstat (limited to 'Documentation/core-api')
-rw-r--r--Documentation/core-api/boot-time-mm.rst92
-rw-r--r--Documentation/core-api/idr.rst2
-rw-r--r--Documentation/core-api/index.rst2
-rw-r--r--Documentation/core-api/timekeeping.rst185
4 files changed, 281 insertions, 0 deletions
diff --git a/Documentation/core-api/boot-time-mm.rst b/Documentation/core-api/boot-time-mm.rst
new file mode 100644
index 000000000000..03cb1643f46f
--- /dev/null
+++ b/Documentation/core-api/boot-time-mm.rst
@@ -0,0 +1,92 @@
+===========================
+Boot time memory management
+===========================
+
+Early system initialization cannot use "normal" memory management
+simply because it is not set up yet. But there is still need to
+allocate memory for various data structures, for instance for the
+physical page allocator. To address this, a specialized allocator
+called the :ref:`Boot Memory Allocator <bootmem>`, or bootmem, was
+introduced. Several years later PowerPC developers added a "Logical
+Memory Blocks" allocator, which was later adopted by other
+architectures and renamed to :ref:`memblock <memblock>`. There is also
+a compatibility layer called `nobootmem` that translates bootmem
+allocation interfaces to memblock calls.
+
+The selection of the early allocator is done using
+``CONFIG_NO_BOOTMEM`` and ``CONFIG_HAVE_MEMBLOCK`` kernel
+configuration options. These options are enabled or disabled
+statically by the architectures' Kconfig files.
+
+* Architectures that rely only on bootmem select
+ ``CONFIG_NO_BOOTMEM=n && CONFIG_HAVE_MEMBLOCK=n``.
+* The users of memblock with the nobootmem compatibility layer set
+ ``CONFIG_NO_BOOTMEM=y && CONFIG_HAVE_MEMBLOCK=y``.
+* And for those that use both memblock and bootmem the configuration
+ includes ``CONFIG_NO_BOOTMEM=n && CONFIG_HAVE_MEMBLOCK=y``.
+
+Whichever allocator is used, it is the responsibility of the
+architecture specific initialization to set it up in
+:c:func:`setup_arch` and tear it down in :c:func:`mem_init` functions.
+
+Once the early memory management is available it offers a variety of
+functions and macros for memory allocations. The allocation request
+may be directed to the first (and probably the only) node or to a
+particular node in a NUMA system. There are API variants that panic
+when an allocation fails and those that don't. And more recent and
+advanced memblock even allows controlling its own behaviour.
+
+.. _bootmem:
+
+Bootmem
+=======
+
+(mostly stolen from Mel Gorman's "Understanding the Linux Virtual
+Memory Manager" `book`_)
+
+.. _book: https://www.kernel.org/doc/gorman/
+
+.. kernel-doc:: mm/bootmem.c
+ :doc: bootmem overview
+
+.. _memblock:
+
+Memblock
+========
+
+.. kernel-doc:: mm/memblock.c
+ :doc: memblock overview
+
+
+Functions and structures
+========================
+
+Common API
+----------
+
+The functions that are described in this section are available
+regardless of what early memory manager is enabled.
+
+.. kernel-doc:: mm/nobootmem.c
+
+Bootmem specific API
+--------------------
+
+These interfaces available only with bootmem, i.e when ``CONFIG_NO_BOOTMEM=n``
+
+.. kernel-doc:: include/linux/bootmem.h
+.. kernel-doc:: mm/bootmem.c
+ :nodocs:
+
+Memblock specific API
+---------------------
+
+Here is the description of memblock data structures, functions and
+macros. Some of them are actually internal, but since they are
+documented it would be silly to omit them. Besides, reading the
+descriptions for the internal functions can help to understand what
+really happens under the hood.
+
+.. kernel-doc:: include/linux/memblock.h
+.. kernel-doc:: mm/memblock.c
+ :nodocs:
diff --git a/Documentation/core-api/idr.rst b/Documentation/core-api/idr.rst
index 9078a5c3ac95..d351e880a2f6 100644
--- a/Documentation/core-api/idr.rst
+++ b/Documentation/core-api/idr.rst
@@ -76,4 +76,6 @@ Functions and structures
========================
.. kernel-doc:: include/linux/idr.h
+ :functions:
.. kernel-doc:: lib/idr.c
+ :functions:
diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst
index f5a66b72f984..b5379fb740a5 100644
--- a/Documentation/core-api/index.rst
+++ b/Documentation/core-api/index.rst
@@ -28,6 +28,8 @@ Core utilities
printk-formats
circular-buffers
gfp_mask-from-fs-io
+ timekeeping
+ boot-time-mm
Interfaces for kernel debugging
===============================
diff --git a/Documentation/core-api/timekeeping.rst b/Documentation/core-api/timekeeping.rst
new file mode 100644
index 000000000000..93cbeb9daec0
--- /dev/null
+++ b/Documentation/core-api/timekeeping.rst
@@ -0,0 +1,185 @@
+ktime accessors
+===============
+
+Device drivers can read the current time using ktime_get() and the many
+related functions declared in linux/timekeeping.h. As a rule of thumb,
+using an accessor with a shorter name is preferred over one with a longer
+name if both are equally fit for a particular use case.
+
+Basic ktime_t based interfaces
+------------------------------
+
+The recommended simplest form returns an opaque ktime_t, with variants
+that return time for different clock references:
+
+
+.. c:function:: ktime_t ktime_get( void )
+
+ CLOCK_MONOTONIC
+
+ Useful for reliable timestamps and measuring short time intervals
+ accurately. Starts at system boot time but stops during suspend.
+
+.. c:function:: ktime_t ktime_get_boottime( void )
+
+ CLOCK_BOOTTIME
+
+ Like ktime_get(), but does not stop when suspended. This can be
+ used e.g. for key expiration times that need to be synchronized
+ with other machines across a suspend operation.
+
+.. c:function:: ktime_t ktime_get_real( void )
+
+ CLOCK_REALTIME
+
+ Returns the time in relative to the UNIX epoch starting in 1970
+ using the Coordinated Universal Time (UTC), same as gettimeofday()
+ user space. This is used for all timestamps that need to
+ persist across a reboot, like inode times, but should be avoided
+ for internal uses, since it can jump backwards due to a leap
+ second update, NTP adjustment settimeofday() operation from user
+ space.
+
+.. c:function:: ktime_t ktime_get_clocktai( void )
+
+ CLOCK_TAI
+
+ Like ktime_get_real(), but uses the International Atomic Time (TAI)
+ reference instead of UTC to avoid jumping on leap second updates.
+ This is rarely useful in the kernel.
+
+.. c:function:: ktime_t ktime_get_raw( void )
+
+ CLOCK_MONOTONIC_RAW
+
+ Like ktime_get(), but runs at the same rate as the hardware
+ clocksource without (NTP) adjustments for clock drift. This is
+ also rarely needed in the kernel.
+
+nanosecond, timespec64, and second output
+-----------------------------------------
+
+For all of the above, there are variants that return the time in a
+different format depending on what is required by the user:
+
+.. c:function:: u64 ktime_get_ns( void )
+ u64 ktime_get_boottime_ns( void )
+ u64 ktime_get_real_ns( void )
+ u64 ktime_get_tai_ns( void )
+ u64 ktime_get_raw_ns( void )
+
+ Same as the plain ktime_get functions, but returning a u64 number
+ of nanoseconds in the respective time reference, which may be
+ more convenient for some callers.
+
+.. c:function:: void ktime_get_ts64( struct timespec64 * )
+ void ktime_get_boottime_ts64( struct timespec64 * )
+ void ktime_get_real_ts64( struct timespec64 * )
+ void ktime_get_clocktai_ts64( struct timespec64 * )
+ void ktime_get_raw_ts64( struct timespec64 * )
+
+ Same above, but returns the time in a 'struct timespec64', split
+ into seconds and nanoseconds. This can avoid an extra division
+ when printing the time, or when passing it into an external
+ interface that expects a 'timespec' or 'timeval' structure.
+
+.. c:function:: time64_t ktime_get_seconds( void )
+ time64_t ktime_get_boottime_seconds( void )
+ time64_t ktime_get_real_seconds( void )
+ time64_t ktime_get_clocktai_seconds( void )
+ time64_t ktime_get_raw_seconds( void )
+
+ Return a coarse-grained version of the time as a scalar
+ time64_t. This avoids accessing the clock hardware and rounds
+ down the seconds to the full seconds of the last timer tick
+ using the respective reference.
+
+Coarse and fast_ns access
+-------------------------
+
+Some additional variants exist for more specialized cases:
+
+.. c:function:: ktime_t ktime_get_coarse_boottime( void )
+ ktime_t ktime_get_coarse_real( void )
+ ktime_t ktime_get_coarse_clocktai( void )
+ ktime_t ktime_get_coarse_raw( void )
+
+.. c:function:: void ktime_get_coarse_ts64( struct timespec64 * )
+ void ktime_get_coarse_boottime_ts64( struct timespec64 * )
+ void ktime_get_coarse_real_ts64( struct timespec64 * )
+ void ktime_get_coarse_clocktai_ts64( struct timespec64 * )
+ void ktime_get_coarse_raw_ts64( struct timespec64 * )
+
+ These are quicker than the non-coarse versions, but less accurate,
+ corresponding to CLOCK_MONONOTNIC_COARSE and CLOCK_REALTIME_COARSE
+ in user space, along with the equivalent boottime/tai/raw
+ timebase not available in user space.
+
+ The time returned here corresponds to the last timer tick, which
+ may be as much as 10ms in the past (for CONFIG_HZ=100), same as
+ reading the 'jiffies' variable. These are only useful when called
+ in a fast path and one still expects better than second accuracy,
+ but can't easily use 'jiffies', e.g. for inode timestamps.
+ Skipping the hardware clock access saves around 100 CPU cycles
+ on most modern machines with a reliable cycle counter, but
+ up to several microseconds on older hardware with an external
+ clocksource.
+
+.. c:function:: u64 ktime_get_mono_fast_ns( void )
+ u64 ktime_get_raw_fast_ns( void )
+ u64 ktime_get_boot_fast_ns( void )
+ u64 ktime_get_real_fast_ns( void )
+
+ These variants are safe to call from any context, including from
+ a non-maskable interrupt (NMI) during a timekeeper update, and
+ while we are entering suspend with the clocksource powered down.
+ This is useful in some tracing or debugging code as well as
+ machine check reporting, but most drivers should never call them,
+ since the time is allowed to jump under certain conditions.
+
+Deprecated time interfaces
+--------------------------
+
+Older kernels used some other interfaces that are now being phased out
+but may appear in third-party drivers being ported here. In particular,
+all interfaces returning a 'struct timeval' or 'struct timespec' have
+been replaced because the tv_sec member overflows in year 2038 on 32-bit
+architectures. These are the recommended replacements:
+
+.. c:function:: void ktime_get_ts( struct timespec * )
+
+ Use ktime_get() or ktime_get_ts64() instead.
+
+.. c:function:: struct timeval do_gettimeofday( void )
+ struct timespec getnstimeofday( void )
+ struct timespec64 getnstimeofday64( void )
+ void ktime_get_real_ts( struct timespec * )
+
+ ktime_get_real_ts64() is a direct replacement, but consider using
+ monotonic time (ktime_get_ts64()) and/or a ktime_t based interface
+ (ktime_get()/ktime_get_real()).
+
+.. c:function:: struct timespec current_kernel_time( void )
+ struct timespec64 current_kernel_time64( void )
+ struct timespec get_monotonic_coarse( void )
+ struct timespec64 get_monotonic_coarse64( void )
+
+ These are replaced by ktime_get_coarse_real_ts64() and
+ ktime_get_coarse_ts64(). However, A lot of code that wants
+ coarse-grained times can use the simple 'jiffies' instead, while
+ some drivers may actually want the higher resolution accessors
+ these days.
+
+.. c:function:: struct timespec getrawmonotonic( void )
+ struct timespec64 getrawmonotonic64( void )
+ struct timespec timekeeping_clocktai( void )
+ struct timespec64 timekeeping_clocktai64( void )
+ struct timespec get_monotonic_boottime( void )
+ struct timespec64 get_monotonic_boottime64( void )
+
+ These are replaced by ktime_get_raw()/ktime_get_raw_ts64(),
+ ktime_get_clocktai()/ktime_get_clocktai_ts64() as well
+ as ktime_get_boottime()/ktime_get_boottime_ts64().
+ However, if the particular choice of clock source is not
+ important for the user, consider converting to
+ ktime_get()/ktime_get_ts64() instead for consistency.