文章目录
前言
system request (SysRq) keys:是预定义的(在内核中硬编码)键组合,可触发各种操作。
It is a ‘magical’ key combo you can hit which the kernel will respond to regardless of whatever else it is doing, unless it is completely locked up.
Sysrq被称为”魔术组合键”, 是内建于Linux内核的调试工具,只要内核没有完全锁住,不管内核在做什么事情,内核都会响应这一系列组合键,使用这些组合键可以搜集包括系统内存使用、CPU任务处理、进程运行状态等系统运行信息。
SysRq 键在确认内核运行、调查内核死机原因等各种情况下都非常有效。
一、SysRq简介
要想使用 Magic SysRq key 打开内核配置选项 CONFIG_MAGIC_SYSRQ,一般的发行版都默认打开该配置选项:
#
# Kernel hacking
#
......
CONFIG_MAGIC_SYSRQ=y
当运行一个编译了SysRq的内核时,/proc/sys/kernel/sysrq文件的值控制着允许通过SysRq键(键盘组合键)调用的函数,下面是/proc/sys/kernel/sysrq中可能的值列表:
0 - disable sysrq completely
1 - enable all functions of sysrq
>1 - bitmask of allowed sysrq functions (see below for detailed function description):
2 = 0x2 - enable control of console logging level
4 = 0x4 - enable control of keyboard (SAK, unraw)
8 = 0x8 - enable debugging dumps of processes etc.
16 = 0x10 - enable sync command
32 = 0x20 - enable remount read-only
64 = 0x40 - enable signalling of processes (term, kill, oom-kill)
128 = 0x80 - allow reboot/poweroff
256 = 0x100 - allow nicing of all RT tasks
/proc/sys/kernel/sysrq文件的值控制着SysRq键(键盘组合键)的一些功能。
可以通过以下命令在文件中设置该值:
echo "number" >/proc/sys/kernel/sysrq
比如:
echo 1 >/proc/sys/kernel/sysrq
/proc/sys/kernel/sysrq的值设置为1时,使能SysRq键的所有功能。
或者通过 sysctl 命令也可以设置或者读写内核参数:
sysctl -w kernel.sysrq = 1
NAME
sysctl - configure kernel parameters at runtime
DESCRIPTION
sysctl is used to modify kernel parameters at runtime. The parameters available are those listed under /proc/sys/. Procfs is required for sysctl support in Linux. You
can use sysctl to both read and write sysctl data.
-w, --write
Use this option when you want to change a sysctl setting.
备注:/proc/sys/kernel/sysrq的值只影响通过 键盘组合键的调用。通过/proc/sysrq-trigger调用任何操作总是被允许的(由具有管理权限的用户)。
即 /proc/sys/kernel/sysrq的值 只是影响 键盘组合键触发内核操作,对于 /proc/sysrq-trigger触发内核操作没有影响。
内核配置选项中使能CONFIG_MAGIC_SYSRQ选项,这样系统启动之后,会生成/proc/sysrq-trigger节点用于调试。
二、SysRq的使用
SysRq的使用有两种方式:
第一种是键盘组合键:Alt+SysRq + command key 。(受到/proc/sys/kernel/sysrq值的影响)
第二种是修改/proc/sysrq-trigger文件的值。(不受/proc/sys/kernel/sysrq值的影响)
接下来主要介绍第二种方式:
/proc/sysrq-trigger文件的值不受/proc/sys/kernel/sysrq值的影响,所以我将/proc/sys/kernel/sysrq的值设置为0,依然可以触发内核的各种事件。
[root@localhost ~]# echo 0 > /proc/sys/kernel/sysrq
[root@localhost ~]# cat /proc/sys/kernel/sysrq
0
echo <command key> > /proc/sysrq-trigger
比如:
echo t > /proc/sysrq-trigger
-t 选项把当前的任务快照保存下来,将转储当前任务及其信息的列表到控制台。
SysRq可以很好地追踪系统瞬时状态,即系统快照。
列举一些用于内核调试的command key(区分字母大小写):
Command | Function |
---|---|
c | Will perform a system crash and a crashdump will be taken if configured. |
d | Shows all locks that are held. |
l | Shows a stack backtrace for all active CPUs. |
m | Will dump current memory info to your console. |
p | Will dump the current registers and flags to your console. |
l | Shows a stack backtrace for all active CPUs. |
t | Will dump a list of current tasks and their information to your console. |
w | Dumps tasks that are in uninterruptable (blocked) state. |
SysRq可以观察当前的内存快照、任务快照,可以构造 vmcore 把系统的所有信息都保存下来(-c 选项),甚至还可以在内存紧张的时候用它杀掉内存开销最大的那个进程。
2.1 获取内存快照
echo m > /proc/sysrq-trigger
[580415.132207] SysRq : Show Memory
[580415.132217] Mem-Info:
[580415.132231] active_anon:70197 inactive_anon:8419 isolated_anon:0
active_file:91044 inactive_file:128367 isolated_file:0
unevictable:0 dirty:0 writeback:0 unstable:0
slab_reclaimable:32560 slab_unreclaimable:16646
mapped:24361 shmem:8655 pagetables:5377 bounce:0
free:1569061 free_pcp:1121 free_cma:0
[580415.132243] Node 0 DMA free:15896kB min:136kB low:168kB high:204kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:15992kB managed:15896kB mlocked:0kB dirty:0kB writeback:0kB mapped:0kB shmem:0kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:0kB unstable:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[580415.132259] lowmem_reserve[]: 0 1960 7687 7687
[580415.132267] Node 0 DMA32 free:1619040kB min:17204kB low:21504kB high:25804kB active_anon:77084kB inactive_anon:9124kB active_file:88908kB inactive_file:126020kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:2257312kB managed:2010956kB mlocked:0kB dirty:0kB writeback:0kB mapped:19716kB shmem:9336kB slab_reclaimable:33356kB slab_unreclaimable:11568kB kernel_stack:1408kB pagetables:6192kB unstable:0kB bounce:0kB free_pcp:2264kB local_pcp:308kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[580415.132282] lowmem_reserve[]: 0 0 5726 5726
[580415.132289] Node 0 Normal free:4641308kB min:50240kB low:62800kB high:75360kB active_anon:203704kB inactive_anon:24552kB active_file:275268kB inactive_file:387448kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:5996544kB managed:5863960kB mlocked:0kB dirty:0kB writeback:0kB mapped:77728kB shmem:25284kB slab_reclaimable:96884kB slab_unreclaimable:55016kB kernel_stack:4368kB pagetables:15316kB unstable:0kB bounce:0kB free_pcp:2220kB local_pcp:212kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[580415.132304] lowmem_reserve[]: 0 0 0 0
[580415.132311] Node 0 DMA: 2*4kB (U) 2*8kB (U) 2*16kB (U) 1*32kB (U) 3*64kB (U) 2*128kB (U) 0*256kB 0*512kB 1*1024kB (U) 1*2048kB (M) 3*4096kB (M) = 15896kB
[580415.132339] Node 0 DMA32: 156*4kB (UEM) 140*8kB (UEM) 295*16kB (UEM) 439*32kB (UEM) 251*64kB (UEM) 115*128kB (UM) 34*256kB (UM) 11*512kB (UEM) 3*1024kB (M) 3*2048kB (UM) 377*4096kB (M) = 1619040kB
[580415.132369] Node 0 Normal: 455*4kB (UEM) 630*8kB (UEM) 1329*16kB (UEM) 1244*32kB (UEM) 719*64kB (UEM) 404*128kB (UEM) 243*256kB (UM) 110*512kB (UEM) 63*1024kB (UEM) 70*2048kB (UEM) 1013*4096kB (UM) = 4641308kB
[580415.132401] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=1048576kB
[580415.132406] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
[580415.132409] 228066 total pagecache pages
[580415.132415] 0 pages in swap cache
[580415.132419] Swap cache stats: add 0, delete 0, find 0/0
[580415.132422] Free swap = 8126460kB
[580415.132425] Total swap = 8126460kB
[580415.132428] 2067462 pages RAM
[580415.132431] 0 pages HighMem/MovableOnly
[580415.132434] 94759 pages reserved
2.2 获取任务快照
echo t > /proc/sysrq-trigger
显示了每个任务当前运行的情况和每个CPU当前运行任务的情况:
[580573.523247] SysRq : Show State
[580573.523256] task PC stack pid father
[580573.523262] systemd S ffff9709fcf28000 0 1 0 0x00000000
[580573.523271] Call Trace:
[580573.523285] [<ffffffff9d767bc9>] schedule+0x29/0x70
[580573.523294] [<ffffffff9d766dfd>] schedule_hrtimeout_range_clock+0x12d/0x150
[580573.523305] [<ffffffff9d28e839>] ? ep_scan_ready_list.isra.7+0x1b9/0x1f0
[580573.523312] [<ffffffff9d766e33>] schedule_hrtimeout_range+0x13/0x20
[580573.523319] [<ffffffff9d28eace>] ep_poll+0x23e/0x360
[580573.523328] [<ffffffff9d0d67b0>] ? wake_up_state+0x20/0x20
[580573.523336] [<ffffffff9d28ff9d>] SyS_epoll_wait+0xed/0x120
[580573.523345] [<ffffffff9d774ddb>] system_call_fastpath+0x22/0x27
[580573.523351] kthreadd S ffff9709fcf29040 0 2 0 0x00000000
[580573.523358] Call Trace:
[580573.523366] [<ffffffff9d767bc9>] schedule+0x29/0x70
[580573.523373] [<ffffffff9d0c2625>] kthreadd+0x2f5/0x300
[580573.523381] [<ffffffff9d0c2330>] ? kthread_create_on_cpu+0x60/0x60
[580573.523388] [<ffffffff9d774c1d>] ret_from_fork_nospec_begin+0x7/0x21
[580573.523395] [<ffffffff9d0c2330>] ? kthread_create_on_cpu+0x60/0x60
[580573.523400] ksoftirqd/0 S ffff9709fcf2a080 0 3 2 0x00000000
[580573.523406] Call Trace:
[580573.523413] [<ffffffff9d767bc9>] schedule+0x29/0x70
[580573.523420] [<ffffffff9d0ca562>] smpboot_thread_fn+0xe2/0x1a0
[580573.523426] [<ffffffff9d0ca480>] ? lg_double_unlock+0x40/0x40
[580573.523432] [<ffffffff9d0c1c31>] kthread+0xd1/0xe0
[580573.523439] [<ffffffff9d0c1b60>] ? insert_kthread_work+0x40/0x40
[580573.523446] [<ffffffff9d774c1d>] ret_from_fork_nospec_begin+0x7/0x21
[580573.523453] [<ffffffff9d0c1b60>] ? insert_kthread_work+0x40/0x40
[580573.523457] kworker/0:0H S ffff9709fcf2c100 0 5 2 0x00000000
[580573.523474] Call Trace:
[580573.523483] [<ffffffff9d0b9dea>] ? process_one_work+0x21a/0x440
[580573.523489] [<ffffffff9d767bc9>] schedule+0x29/0x70
[580573.523496] [<ffffffff9d0bae99>] worker_thread+0x1d9/0x3c0
[580573.523504] [<ffffffff9d0bacc0>] ? manage_workers.isra.25+0x2a0/0x2a0
[580573.523509] [<ffffffff9d0c1c31>] kthread+0xd1/0xe0
[580573.523516] [<ffffffff9d0c1b60>] ? insert_kthread_work+0x40/0x40
[580573.523523] [<ffffffff9d774c1d>] ret_from_fork_nospec_begin+0x7/0x21
[580573.523529] [<ffffffff9d0c1b60>] ? insert_kthread_work+0x40/0x40
......
//cpu0 当前运行任务的情况
[580573.538243] cpu#0, 3600.000 MHz
[580573.538244] .nr_running : 0
[580573.538245] .load : 0
[580573.538246] .nr_switches : 20421008
[580573.538247] .nr_load_updates : 11012978
[580573.538247] .nr_uninterruptible : -655
[580573.538248] .next_balance : 4875.237938
[580573.538249] .curr->pid : 0
[580573.538250] .clock : 580573538.220004
[580573.538251] .cpu_load[0] : 0
[580573.538252] .cpu_load[1] : 237
[580573.538252] .cpu_load[2] : 493
[580573.538253] .cpu_load[3] : 655
[580573.538254] .cpu_load[4] : 599
[580573.538254] .avg_idle : 5107
[580573.538255] .max_idle_balance_cost : 500000
[580573.538258] cfs_rq[0]:/
[580573.538259] .exec_clock : 0.000000
[580573.538260] .MIN_vruntime : 0.000001
[580573.538261] .min_vruntime : 2824982.413943
[580573.538262] .max_vruntime : 0.000001
[580573.538263] .spread : 0.000000
[580573.538263] .spread0 : 0.000000
[580573.538264] .nr_spread_over : 0
[580573.538265] .nr_running : 0
[580573.538266] .load : 0
[580573.538266] .runnable_load_avg : 0
[580573.538267] .blocked_load_avg : 317
[580573.538268] .tg_load_avg : 0
[580573.538269] .tg_load_contrib : 0
[580573.538269] .tg_runnable_contrib : 0
[580573.538270] .tg->runnable_avg : 0
[580573.538271] .tg->cfs_bandwidth.timer_active: 0
[580573.538272] .throttled : 0
[580573.538273] .throttle_count : 0
[580573.538274] .avg->runnable_avg_sum : 8138
[580573.538275] .avg->runnable_avg_period : 46352
[580573.538283] rt_rq[0]:/
[580573.538284] .rt_nr_running : 0
[580573.538285] .rt_throttled : 0
[580573.538285] .rt_time : 0.000000
[580573.538286] .rt_runtime : 950.000000
[580573.538288] runnable tasks:
[580573.538289] task PID tree-key switches prio wait-time sum-exec sum-sleep
[580573.538290] ----------------------------------------------------------------------------------------------------------
[580573.538291] ksoftirqd/0 3 2824973.436009 108307 120 0.000000 1680.428964 0.000000 0 /
[580573.538294] kworker/0:0H 5 2776.777100 9 100 0.000000 0.089769 0.000000 0 /
[580573.538296] migration/0 7 0.000000 31932 0 0.000000 272.980359 0.000000 0 /
[580573.538299] rcu_bh 8 38.123474 2 120 0.000000 0.000709 0.000000 0 /
[580573.538301] rcu_sched 9 2824973.474298 1248369 120 0.000000 23413.300648 0.000000 0 /
[580573.538305] lru-add-drain 10 42.124246 2 100 0.000000 0.001218 0.000000 0 /
[580573.538307] watchdog/0 11 -5.967430 145146 0 0.000000 2874.498528 0.000000 0 /
[580573.538312] kmpath_rdacd 62 635.006034 2 100 0.000000 0.012378 0.000000 0 /
[580573.538315] ipv6_addrconf 67 712.678812 2 100 0.000000 0.100476 0.000000 0 /
[580573.538318] scsi_tmf_0 883 1679.281366 2 100 0.000000 0.003571 0.000000 0 /
[580573.538321] scsi_tmf_1 907 1687.801687 2 100 0.000000 0.002658 0.000000 0 /
[580573.538324] scsi_tmf_2 921 1697.538324 2 100 0.000000 0.003882 0.000000 0 /
[580573.538326] scsi_tmf_4 951 1713.204537 2 100 0.000000 0.003118 0.000000 0 /
[580573.538329] scsi_tmf_5 964 1721.307070 2 100 0.000000 0.002513 0.000000 0 /
//cpu当前任务运行的情况
[580573.538547] cpu#1, 3600.000 MHz
......
perf和ftrace一般都是采集一个时间段内的信息,对于追踪系统瞬时状态即系统快照sysrq更合适。
下面是一个脚本来把当前 CPU 正在做的工作记录下来,记录高于CPU运行在内核态时间较多的情况:
[root@localhost ~]# top -bn2 | grep "Cpu(s)" | tail -1
%Cpu(s): 0.3 us, 0.2 sy, 0.0 ni, 99.4 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
[root@localhost ~]# top -bn2 | grep "Cpu(s)" | tail -1 | awk '{print $1, $2, $3, $4, $5}'
%Cpu(s): 0.4 us, 0.2 sy,
#!/bin/sh
while [ 1 ]; do
top -bn2 | grep "Cpu(s)" | tail -1 | awk '{ # $2 is usr, $4 is sys. if ($2 < 30.0 && $4 > 15.0) { # save the current usr and sys into a tmp file while ("date" | getline date) { split(date, str, " "); prefix=sprintf("%s_%s_%s_%s", str[2],str[3], str[4], str[5]); } sys_usr_file=sprintf("/tmp/%s_info.highsys", prefix); print $2 > sys_usr_file; print $4 >> sys_usr_file; # run sysrq system("echo t > /proc/sysrq-trigger"); } }'
sleep 1m
done
这个脚本会检测 sys 利用率高于 15% 同时 usr 较低的情况,也就是说检测 CPU 是否在内核里花费了太多时间。如果出现这种情况,就会运行 sysrq 来保存当前任务快照。
上述代码来自于极客时间:Linux内核技术实战
三、SysRq源码解析
3.1 源码分析
SysRq相关的内核源码在内核驱动目录下:
/drivers/tty/sysrq.c
Magic SysRQ系统通过在key op lookup table上注册键操作来工作,key table在编译时注册了许多操作,但它是可变的,并且导出了 2 个函数作为其接口:
register_sysrq_key and unregister_sysrq_key.
static int __sysrq_swap_key_ops(int key, const struct sysrq_key_op *insert_op_p,
const struct sysrq_key_op *remove_op_p)
{
int retval;
spin_lock(&sysrq_key_table_lock);
if (__sysrq_get_key_op(key) == remove_op_p) {
__sysrq_put_key_op(key, insert_op_p);
retval = 0;
} else {
retval = -1;
}
spin_unlock(&sysrq_key_table_lock);
/* * A concurrent __handle_sysrq either got the old op or the new op. * Wait for it to go away before returning, so the code for an old * op is not freed (eg. on module unload) while it is in use. */
synchronize_rcu();
return retval;
}
int register_sysrq_key(int key, const struct sysrq_key_op *op_p)
{
return __sysrq_swap_key_ops(key, op_p, NULL);
}
EXPORT_SYMBOL(register_sysrq_key);
int unregister_sysrq_key(int key, const struct sysrq_key_op *op_p)
{
return __sysrq_swap_key_ops(key, NULL, op_p);
}
EXPORT_SYMBOL(unregister_sysrq_key);
/* Key Operations table and lock */
static DEFINE_SPINLOCK(sysrq_key_table_lock);
static const struct sysrq_key_op *sysrq_key_table[62] = {
&sysrq_loglevel_op, /* 0 */
&sysrq_loglevel_op, /* 1 */
&sysrq_loglevel_op, /* 2 */
&sysrq_loglevel_op, /* 3 */
&sysrq_loglevel_op, /* 4 */
&sysrq_loglevel_op, /* 5 */
&sysrq_loglevel_op, /* 6 */
&sysrq_loglevel_op, /* 7 */
&sysrq_loglevel_op, /* 8 */
&sysrq_loglevel_op, /* 9 */
/* * a: Don't use for system provided sysrqs, it is handled specially on * sparc and will never arrive. */
NULL, /* a */
&sysrq_reboot_op, /* b */
&sysrq_crash_op, /* c */
&sysrq_showlocks_op, /* d */
&sysrq_term_op, /* e */
&sysrq_moom_op, /* f */
/* g: May be registered for the kernel debugger */
NULL, /* g */
NULL, /* h - reserved for help */
&sysrq_kill_op, /* i */
&sysrq_thaw_op, /* j */
&sysrq_SAK_op, /* k */
&sysrq_showallcpus_op, /* l */
&sysrq_showmem_op, /* m */
&sysrq_unrt_op, /* n */
/* o: This will often be registered as 'Off' at init time */
NULL, /* o */
&sysrq_showregs_op, /* p */
&sysrq_show_timers_op, /* q */
&sysrq_unraw_op, /* r */
&sysrq_sync_op, /* s */
&sysrq_showstate_op, /* t */
&sysrq_mountro_op, /* u */
/* v: May be registered for frame buffer console restore */
NULL, /* v */
&sysrq_showstate_blocked_op, /* w */
/* x: May be registered on mips for TLB dump */
/* x: May be registered on ppc/powerpc for xmon */
/* x: May be registered on sparc64 for global PMU dump */
NULL, /* x */
/* y: May be registered on sparc64 for global register dump */
NULL, /* y */
&sysrq_ftrace_dump_op, /* z */
NULL, /* A */
NULL, /* B */
NULL, /* C */
......
}
static int __init sysrq_init(void)
{
(1) 初始化/proc/sysrq-trigger , 通过 /proc/sysrq-trigger 文件的值触发内核操作
sysrq_init_procfs();
(2) 初始化组合键 Alt + SysRq + key , 通过组合键 Alt + SysRq + key 触发内核操作
if (sysrq_on())
sysrq_register_handler();
return 0;
}
device_initcall(sysrq_init);
(1)/proc/sysrq-trigger
#ifdef CONFIG_PROC_FS
/* * writing 'C' to /proc/sysrq-trigger is like sysrq-C */
static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
if (count) {
char c;
if (get_user(c, buf))
return -EFAULT;
__handle_sysrq(c, false);
}
return count;
}
static const struct proc_ops sysrq_trigger_proc_ops = {
.proc_write = write_sysrq_trigger,
.proc_lseek = noop_llseek,
};
static void sysrq_init_procfs(void)
{
if (!proc_create("sysrq-trigger", S_IWUSR, NULL,
&sysrq_trigger_proc_ops))
pr_err("Failed to register proc interface\n");
}
#endif /* CONFIG_PROC_FS */
执行 echo > /proc/sysrq-trigger 就会调用 __handle_sysrq 函数,找到sysrq_key_table表中对应的操作函数。
/* * get and put functions for the table, exposed to modules. */
static const struct sysrq_key_op *__sysrq_get_key_op(int key)
{
const struct sysrq_key_op *op_p = NULL;
int i;
i = sysrq_key_table_key2index(key);
if (i != -1)
op_p = sysrq_key_table[i];
return op_p;
}
void __handle_sysrq(int key, bool check_mask)
{
const struct sysrq_key_op *op_p;
......
rcu_sysrq_start();
rcu_read_lock();
op_p = __sysrq_get_key_op(key);
if (op_p) {
/* * Should we check for enabled operations (/proc/sysrq-trigger * should not) and is the invoked operation enabled? */
if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
......
op_p->handler(key);
}
}
rcu_read_unlock();
rcu_sysrq_end();
......
}
(2) 初始化组合键 Alt + SysRq + key
static struct input_handler sysrq_handler = {
.filter = sysrq_filter,
.connect = sysrq_connect,
.disconnect = sysrq_disconnect,
.name = "sysrq",
.id_table = sysrq_ids,
};
static inline void sysrq_register_handler(void)
{
int error;
sysrq_of_get_keyreset_config();
error = input_register_handler(&sysrq_handler);
if (error)
pr_err("Failed to register input handler, error %d", error);
}
static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
unsigned int code, int value)
{
......
default:
if (sysrq->active && value && value != 2) {
unsigned char c = sysrq_xlate[code];
sysrq->need_reinject = false;
if (sysrq->shift_use != KEY_RESERVED)
c = toupper(c);
__handle_sysrq(c, true);
}
break;
}
......
return suppress;
}
static bool sysrq_filter(struct input_handle *handle,
unsigned int type, unsigned int code, int value)
{
struct sysrq_state *sysrq = handle->private;
bool suppress;
/* * Do not filter anything if we are in the process of re-injecting * Alt+SysRq combination. */
if (sysrq->reinjecting)
return false;
switch (type) {
......
case EV_KEY:
suppress = sysrq_handle_keypress(sysrq, code, value);
break;
......
}
return suppress;
组合键 Alt + SysRq + key 最终也会调用 和 设置 /proc/sysrq-trigger 的值一样调用 __handle_sysrq 函数。
3.2 源码例程分析
比如执行 echo t > /proc/sysrq-trigger,就会在sysrq_key_table表中找到sysrq_showstate_op:
static const struct sysrq_key_op *sysrq_key_table[62] = {
......
&sysrq_showstate_op, /* t */
......
}
然后执行 sysrq_showstate_op ->handler():
static void sysrq_handle_showstate(int key)
{
show_state();
show_all_workqueues();
}
static const struct sysrq_key_op sysrq_showstate_op = {
.handler = sysrq_handle_showstate,
.help_msg = "show-task-states(t)",
.action_msg = "Show State",
.enable_mask = SYSRQ_ENABLE_DUMP,
};
最终执行sysrq_handle_showstate函数。
3.3 add SysRQ key events to a module
// /include/linux/sysrq.h
struct sysrq_key_op {
void (* const handler)(int);
const char * const help_msg;
const char * const action_msg;
const int enable_mask;
};
#ifdef CONFIG_MAGIC_SYSRQ
/* Generic SysRq interface -- you may call it from any device driver, supplying * ASCII code of the key, pointer to registers and kbd/tty structs (if they * are available -- else NULL's). */
void handle_sysrq(int key);
void __handle_sysrq(int key, bool check_mask);
int register_sysrq_key(int key, const struct sysrq_key_op *op);
int unregister_sysrq_key(int key, const struct sysrq_key_op *op);
为了在表中注册一个基本函数,你必须首先包含头include/linux/sysrq.h,这将定义你需要的所有其他东西。接下来,您必须创建一个sysrq_key_op结构体,填充sysrq_key_op结构体:
A) the key handler function you will use.
B) a help_msg string, that will print when SysRQ prints help.
C) an action_msg string, that will print right before your handler is called.
the key handler function 必须符合’ sysrq.h ‘中的原型:void (* const handler)(int)。
创建sysrq_key_op后,就可以调用 register_sysrq_key(int key, const struct sysrq_key_op *op_p) 登记 sysrq 操作。
在模块卸载时,调用 unregister_sysrq_key(int key, const struct sysrq_key_op *op_p) 注销 sysrq 操作。
当然,永远不要在表中留下无效的指针。也就是说,当调用register_sysrq_key()的模块退出时,它必须调用unregister_sysrq_key()来清理它使用的sysrq键表项。空指针在表中总是安全的。
After the sysrq_key_op is created, you can call the kernel function register_sysrq_key(int key, const struct sysrq_key_op *op_p); this will register the operation pointed to by op_p at table key ‘key’, if that slot in the table is blank. At module unload time, you must call the function unregister_sysrq_key(int key, const struct sysrq_key_op *op_p), which will remove the key op pointed to by ‘op_p’ from the key ‘key’, if and only if it is currently registered in that slot. This is in case the slot has been overwritten since you registered it.
参考资料
极客时间:Linux内核技术实战
https://static.lwn.net/kerneldoc/admin-guide/sysrq.html
https://elixir.bootlin.com/linux/v6.0/source/drivers/tty/sysrq.c
Linux 调试之SysRq
Linux 调试之SysRq
Linux 调试之SysRq
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