1<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Kernel utility functions</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="Linux Device Drivers"><link rel="up" href="Basics.html" title="Chapter 1. Driver Basics"><link rel="prev" href="API-kset-create-and-add.html" title="kset_create_and_add"><link rel="next" href="API-upper-32-bits.html" title="upper_32_bits"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Kernel utility functions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="API-kset-create-and-add.html">Prev</a> </td><th width="60%" align="center">Chapter 1. Driver Basics</th><td width="20%" align="right"> <a accesskey="n" href="API-upper-32-bits.html">Next</a></td></tr></table><hr></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id-1.3.10"></a>Kernel utility functions</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="refentrytitle"><a href="API-upper-32-bits.html"><span class="phrase">upper_32_bits</span></a></span><span class="refpurpose"> — 2 return bits 32-63 of a number 3 </span></dt><dt><span class="refentrytitle"><a href="API-lower-32-bits.html"><span class="phrase">lower_32_bits</span></a></span><span class="refpurpose"> — 4 return bits 0-31 of a number 5 </span></dt><dt><span class="refentrytitle"><a href="API-might-sleep.html"><span class="phrase">might_sleep</span></a></span><span class="refpurpose"> — 6 annotation for functions that can sleep 7 </span></dt><dt><span class="refentrytitle"><a href="API-abs.html"><span class="phrase">abs</span></a></span><span class="refpurpose"> — 8 return absolute value of an argument 9 </span></dt><dt><span class="refentrytitle"><a href="API-reciprocal-scale.html"><span class="phrase">reciprocal_scale</span></a></span><span class="refpurpose"> — 10 "scale" a value into range [0, ep_ro) 11 </span></dt><dt><span class="refentrytitle"><a href="API-kstrtoul.html"><span class="phrase">kstrtoul</span></a></span><span class="refpurpose"> — 12 convert a string to an unsigned long 13 </span></dt><dt><span class="refentrytitle"><a href="API-kstrtol.html"><span class="phrase">kstrtol</span></a></span><span class="refpurpose"> — 14 convert a string to a long 15 </span></dt><dt><span class="refentrytitle"><a href="API-trace-printk.html"><span class="phrase">trace_printk</span></a></span><span class="refpurpose"> — 16 printf formatting in the ftrace buffer 17 </span></dt><dt><span class="refentrytitle"><a href="API-trace-puts.html"><span class="phrase">trace_puts</span></a></span><span class="refpurpose"> — 18 write a string into the ftrace buffer 19 </span></dt><dt><span class="refentrytitle"><a href="API-min-not-zero.html"><span class="phrase">min_not_zero</span></a></span><span class="refpurpose"> — 20 return the minimum that is _not_ zero, unless both are zero 21 </span></dt><dt><span class="refentrytitle"><a href="API-clamp.html"><span class="phrase">clamp</span></a></span><span class="refpurpose"> — 22 return a value clamped to a given range with strict typechecking 23 </span></dt><dt><span class="refentrytitle"><a href="API-clamp-t.html"><span class="phrase">clamp_t</span></a></span><span class="refpurpose"> — 24 return a value clamped to a given range using a given type 25 </span></dt><dt><span class="refentrytitle"><a href="API-clamp-val.html"><span class="phrase">clamp_val</span></a></span><span class="refpurpose"> — 26 return a value clamped to a given range using val's type 27 </span></dt><dt><span class="refentrytitle"><a href="API-container-of.html"><span class="phrase">container_of</span></a></span><span class="refpurpose"> — 28 cast a member of a structure out to the containing structure 29 </span></dt><dt><span class="refentrytitle"><a href="API-printk.html"><span class="phrase">printk</span></a></span><span class="refpurpose"> — 30 print a kernel message 31 </span></dt><dt><span class="refentrytitle"><a href="API-console-lock.html"><span class="phrase">console_lock</span></a></span><span class="refpurpose"> — 32 lock the console system for exclusive use. 33 </span></dt><dt><span class="refentrytitle"><a href="API-console-trylock.html"><span class="phrase">console_trylock</span></a></span><span class="refpurpose"> — 34 try to lock the console system for exclusive use. 35 </span></dt><dt><span class="refentrytitle"><a href="API-console-unlock.html"><span class="phrase">console_unlock</span></a></span><span class="refpurpose"> — 36 unlock the console system 37 </span></dt><dt><span class="refentrytitle"><a href="API-console-conditional-schedule.html"><span class="phrase">console_conditional_schedule</span></a></span><span class="refpurpose"> — 38 yield the CPU if required 39 </span></dt><dt><span class="refentrytitle"><a href="API-printk-timed-ratelimit.html"><span class="phrase">printk_timed_ratelimit</span></a></span><span class="refpurpose"> — 40 caller-controlled printk ratelimiting 41 </span></dt><dt><span class="refentrytitle"><a href="API-kmsg-dump-register.html"><span class="phrase">kmsg_dump_register</span></a></span><span class="refpurpose"> — 42 register a kernel log dumper. 43 </span></dt><dt><span class="refentrytitle"><a href="API-kmsg-dump-unregister.html"><span class="phrase">kmsg_dump_unregister</span></a></span><span class="refpurpose"> — 44 unregister a kmsg dumper. 45 </span></dt><dt><span class="refentrytitle"><a href="API-kmsg-dump-get-line.html"><span class="phrase">kmsg_dump_get_line</span></a></span><span class="refpurpose"> — 46 retrieve one kmsg log line 47 </span></dt><dt><span class="refentrytitle"><a href="API-kmsg-dump-get-buffer.html"><span class="phrase">kmsg_dump_get_buffer</span></a></span><span class="refpurpose"> — 48 copy kmsg log lines 49 </span></dt><dt><span class="refentrytitle"><a href="API-kmsg-dump-rewind.html"><span class="phrase">kmsg_dump_rewind</span></a></span><span class="refpurpose"> — 50 reset the interator 51 </span></dt><dt><span class="refentrytitle"><a href="API-panic.html"><span class="phrase">panic</span></a></span><span class="refpurpose"> — 52 halt the system 53 </span></dt><dt><span class="refentrytitle"><a href="API-add-taint.html"><span class="phrase">add_taint</span></a></span><span class="refpurpose"> — 54 </span></dt><dt><span class="refentrytitle"><a href="re230.html"> 55 kernel/sys.c 56 </a></span><span class="refpurpose"> — 57 Document generation inconsistency 58 </span></dt><dt><span class="refentrytitle"><a href="API-init-srcu-struct.html"><span class="phrase">init_srcu_struct</span></a></span><span class="refpurpose"> — 59 initialize a sleep-RCU structure 60 </span></dt><dt><span class="refentrytitle"><a href="API-cleanup-srcu-struct.html"><span class="phrase">cleanup_srcu_struct</span></a></span><span class="refpurpose"> — 61 deconstruct a sleep-RCU structure 62 </span></dt><dt><span class="refentrytitle"><a href="API-synchronize-srcu.html"><span class="phrase">synchronize_srcu</span></a></span><span class="refpurpose"> — 63 wait for prior SRCU read-side critical-section completion 64 </span></dt><dt><span class="refentrytitle"><a href="API-synchronize-srcu-expedited.html"><span class="phrase">synchronize_srcu_expedited</span></a></span><span class="refpurpose"> — 65 Brute-force SRCU grace period 66 </span></dt><dt><span class="refentrytitle"><a href="API-srcu-barrier.html"><span class="phrase">srcu_barrier</span></a></span><span class="refpurpose"> — 67 Wait until all in-flight <code class="function">call_srcu</code> callbacks complete. 68 </span></dt><dt><span class="refentrytitle"><a href="API-srcu-batches-completed.html"><span class="phrase">srcu_batches_completed</span></a></span><span class="refpurpose"> — 69 return batches completed. 70 </span></dt><dt><span class="refentrytitle"><a href="API-rcu-idle-enter.html"><span class="phrase">rcu_idle_enter</span></a></span><span class="refpurpose"> — 71 inform RCU that current CPU is entering idle 72 </span></dt><dt><span class="refentrytitle"><a href="API-rcu-idle-exit.html"><span class="phrase">rcu_idle_exit</span></a></span><span class="refpurpose"> — 73 inform RCU that current CPU is leaving idle 74 </span></dt><dt><span class="refentrytitle"><a href="API-rcu-is-watching.html"><span class="phrase">rcu_is_watching</span></a></span><span class="refpurpose"> — 75 see if RCU thinks that the current CPU is idle 76 </span></dt><dt><span class="refentrytitle"><a href="API-synchronize-sched.html"><span class="phrase">synchronize_sched</span></a></span><span class="refpurpose"> — 77 wait until an rcu-sched grace period has elapsed. 78 </span></dt><dt><span class="refentrytitle"><a href="API-synchronize-rcu-bh.html"><span class="phrase">synchronize_rcu_bh</span></a></span><span class="refpurpose"> — 79 wait until an rcu_bh grace period has elapsed. 80 </span></dt><dt><span class="refentrytitle"><a href="API-get-state-synchronize-rcu.html"><span class="phrase">get_state_synchronize_rcu</span></a></span><span class="refpurpose"> — 81 Snapshot current RCU state 82 </span></dt><dt><span class="refentrytitle"><a href="API-cond-synchronize-rcu.html"><span class="phrase">cond_synchronize_rcu</span></a></span><span class="refpurpose"> — 83 Conditionally wait for an RCU grace period 84 </span></dt><dt><span class="refentrytitle"><a href="API-get-state-synchronize-sched.html"><span class="phrase">get_state_synchronize_sched</span></a></span><span class="refpurpose"> — 85 Snapshot current RCU-sched state 86 </span></dt><dt><span class="refentrytitle"><a href="API-cond-synchronize-sched.html"><span class="phrase">cond_synchronize_sched</span></a></span><span class="refpurpose"> — 87 Conditionally wait for an RCU-sched grace period 88 </span></dt><dt><span class="refentrytitle"><a href="API-synchronize-sched-expedited.html"><span class="phrase">synchronize_sched_expedited</span></a></span><span class="refpurpose"> — 89 Brute-force RCU-sched grace period 90 </span></dt><dt><span class="refentrytitle"><a href="API-rcu-barrier-bh.html"><span class="phrase">rcu_barrier_bh</span></a></span><span class="refpurpose"> — 91 Wait until all in-flight <code class="function">call_rcu_bh</code> callbacks complete. 92 </span></dt><dt><span class="refentrytitle"><a href="API-rcu-barrier-sched.html"><span class="phrase">rcu_barrier_sched</span></a></span><span class="refpurpose"> — 93 Wait for in-flight <code class="function">call_rcu_sched</code> callbacks. 94 </span></dt><dt><span class="refentrytitle"><a href="API-synchronize-rcu.html"><span class="phrase">synchronize_rcu</span></a></span><span class="refpurpose"> — 95 wait until a grace period has elapsed. 96 </span></dt><dt><span class="refentrytitle"><a href="API-synchronize-rcu-expedited.html"><span class="phrase">synchronize_rcu_expedited</span></a></span><span class="refpurpose"> — 97 Brute-force RCU grace period 98 </span></dt><dt><span class="refentrytitle"><a href="API-rcu-barrier.html"><span class="phrase">rcu_barrier</span></a></span><span class="refpurpose"> — 99 Wait until all in-flight <code class="function">call_rcu</code> callbacks complete. 100 </span></dt><dt><span class="refentrytitle"><a href="API-rcu-read-lock-sched-held.html"><span class="phrase">rcu_read_lock_sched_held</span></a></span><span class="refpurpose"> — 101 might we be in RCU-sched read-side critical section? 102 </span></dt><dt><span class="refentrytitle"><a href="API-rcu-expedite-gp.html"><span class="phrase">rcu_expedite_gp</span></a></span><span class="refpurpose"> — 103 Expedite future RCU grace periods 104 </span></dt><dt><span class="refentrytitle"><a href="API-rcu-unexpedite-gp.html"><span class="phrase">rcu_unexpedite_gp</span></a></span><span class="refpurpose"> 105 Cancel prior rcu_expedite_gp invocation 106 </span></dt><dt><span class="refentrytitle"><a href="API-rcu-read-lock-held.html"><span class="phrase">rcu_read_lock_held</span></a></span><span class="refpurpose"> — 107 might we be in RCU read-side critical section? 108 </span></dt><dt><span class="refentrytitle"><a href="API-rcu-read-lock-bh-held.html"><span class="phrase">rcu_read_lock_bh_held</span></a></span><span class="refpurpose"> — 109 might we be in RCU-bh read-side critical section? 110 </span></dt><dt><span class="refentrytitle"><a href="API-wakeme-after-rcu.html"><span class="phrase">wakeme_after_rcu</span></a></span><span class="refpurpose"> — 111 Callback function to awaken a task after grace period 112 </span></dt><dt><span class="refentrytitle"><a href="API-init-rcu-head-on-stack.html"><span class="phrase">init_rcu_head_on_stack</span></a></span><span class="refpurpose"> — 113 initialize on-stack rcu_head for debugobjects 114 </span></dt><dt><span class="refentrytitle"><a href="API-destroy-rcu-head-on-stack.html"><span class="phrase">destroy_rcu_head_on_stack</span></a></span><span class="refpurpose"> — 115 destroy on-stack rcu_head for debugobjects 116 </span></dt><dt><span class="refentrytitle"><a href="API-synchronize-rcu-tasks.html"><span class="phrase">synchronize_rcu_tasks</span></a></span><span class="refpurpose"> — 117 wait until an rcu-tasks grace period has elapsed. 118 </span></dt><dt><span class="refentrytitle"><a href="API-rcu-barrier-tasks.html"><span class="phrase">rcu_barrier_tasks</span></a></span><span class="refpurpose"> — 119 Wait for in-flight <code class="function">call_rcu_tasks</code> callbacks. 120 </span></dt></dl></div></div><div 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