引用

• Dynamic debug — The Linux Kernel documentation

一. 什么叫dynamic debug？

Dynamic debug allows you to dynamically enable/disable kernel debug-print code to obtain additional kernel information.

If /proc/dynamic_debug/control exists, your kernel has dynamic debug. You’ll need root access (sudo su) to use this.

Dynamic debug provides:

• a Catalog of all prdbgs in your kernel. cat /proc/dynamic_debug/control to see them.

• a Simple query/command language to alter prdbgs by selecting on any combination of 0 or 1 of:

• source filename

• function name

• line number (including ranges of line numbers)

• module name

• format string

• class name (as known/declared by each module)

二. 内核API

pr_debug()
dev_dbg()
print_hex_dump_debug()
print_hex_dump_bytes()

• printk.h - include/linux/printk.h - Linux source code (v6.2.6) - Bootlin

/* If you are writing a driver, please use dev_dbg instead */
#if defined(CONFIG_DYNAMIC_DEBUG) || \(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
#include /*** pr_debug - Print a debug-level message conditionally* @fmt: format string* @...: arguments for the format string** This macro expands to dynamic_pr_debug() if CONFIG_DYNAMIC_DEBUG is* set. Otherwise, if DEBUG is defined, it's equivalent to a printk with* KERN_DEBUG loglevel. If DEBUG is not defined it does nothing.** It uses pr_fmt() to generate the format string (dynamic_pr_debug() uses* pr_fmt() internally).*/
#define pr_debug(fmt, ...)            \dynamic_pr_debug(fmt, ##__VA_ARGS__)
#elif defined(DEBUG)
#define pr_debug(fmt, ...) \printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
#else
#define pr_debug(fmt, ...) \no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
#endif

• dev_printk.h - include/linux/dev_printk.h - Linux source code (v6.2.6) - Bootlin

#if defined(CONFIG_DYNAMIC_DEBUG) || \(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
#define dev_dbg(dev, fmt, ...)                        \dynamic_dev_dbg(dev, dev_fmt(fmt), ##__VA_ARGS__)
#elif defined(DEBUG)
#define dev_dbg(dev, fmt, ...)                        \dev_printk(KERN_DEBUG, dev, dev_fmt(fmt), ##__VA_ARGS__)
#else
#define dev_dbg(dev, fmt, ...)                        \
({                                    \if (0)                                \dev_printk(KERN_DEBUG, dev, dev_fmt(fmt), ##__VA_ARGS__); \
})
#endif

三.相关配置

3.1 内核配置和DEBUG宏是如何影响dynamic debug API的输出的？

3.2 如何检查配置？

• CONFIG_DYNAMIC_DEBUG, CONFIG_DEBUG_FS

在系统的编译配置文件 config中，如果为y，表示开启，为n，表示关闭。

• DEBUG

1. 方法1：在内核模块c源文件最开始处定义。

#define DEBUG//其他源码
xxxx

2. 方法2：在内核模块的Makefile中定义。

ccflags-y += -DDEBUG

四. 如何控制dynamic debug logging？

4.1 在系统启动时

在系统启动参数中添加rule，rule为dynamic debug的控制规则。"QUERY"代表控制规则。

dyndbg="QUERY"
module.dyndbg="QUERY"

4.2 在内核模块加载时（foo为示例内核模块名）

当一个内核模块加载时， 会按照以下顺序检查以下三个设定。

When modprobe foo is called, modprobe scans /proc/cmdline for foo.params, strips foo., and passes them to the kernel along with params given in modprobe args or /etc/modprob.d/*.conf files, in the following order:

1. parameters given via /etc/modprobe.d/*.conf:

options foo dyndbg=+pt
options foo dyndbg # defaults to +p

2. foo.dyndbg as given in boot args, foo. is stripped and passed:

foo.dyndbg=" func bar +p; func buz +mp"

3. args to modprobe:

modprobe foo dyndbg==pmf # override previous settings

4.2 在内核模块runing时

echo "module module_name +p" > /proc/dynamic_debug/control// enable the message at line 1603 of file svcsock.c
:#> ddcmd 'file svcsock.c line 1603 +p'// enable all the messages in file svcsock.c
:#> ddcmd 'file svcsock.c +p'// enable all the messages in the NFS server module
:#> ddcmd 'module nfsd +p'// enable all 12 messages in the function svc_process()
:#> ddcmd 'func svc_process +p'// disable all 12 messages in the function svc_process()
:#> ddcmd 'func svc_process -p'// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
:#> ddcmd 'format "nfsd: READ" +p'// enable messages in files of which the paths include string "usb"
:#> ddcmd 'file *usb* +p' > /proc/dynamic_debug/control// enable all messages
:#> ddcmd '+p' > /proc/dynamic_debug/control// add module, function to all enabled messages
:#> ddcmd '+mf' > /proc/dynamic_debug/control// boot-args example, with newlines and comments for readability
Kernel command line: ...// see what's going on in dyndbg=value processingdynamic_debug.verbose=3// enable pr_debugs in the btrfs module (can be builtin or loadable)btrfs.dyndbg="+p"// enable pr_debugs in all files under init/// and the function parse_one, #cmt is strippeddyndbg="file init/* +p #cmt ; func parse_one +p"// enable pr_debugs in 2 functions in a module loaded laterpc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p"

五. 示例

• Makefile

#ccflags-y += -DDEBUGobj-m += test.oall:make -C /lib/modules/`uname -r`/build M=$(PWD) modules
clean:make -C /lib/modules/`uname -r`/build M=$(PWD) clean

• source code

//#define DEBUG#include 
#include 
#include 
#include static int __init init_my_module(void) {pr_debug("i'm %s\n", "pr_debug");pr_info("i'm %s\n", "pr_info");pr_notice("i'm %s\n", "pr_notice");pr_warn("i'm %s\n", "pr_warn");pr_err("i'm %s\n", "pr_err");pr_crit("i'm %s\n", "pr_crit");pr_alert("i'm %s\n", "pr_alert");pr_emerg("i'm %s\n", "pr_emerg");dev_dbg(NULL, "i'm %s\n", "dev_dbg");dev_info(NULL, "i'm %s\n", "dev_info");dev_notice(NULL, "i'm %s\n", "dev_notice");dev_warn(NULL, "i'm %s\n", "dev_warn");dev_err(NULL, "i'm %s\n", "dev_err");dev_crit(NULL, "i'm %s\n", "dev_crit");dev_alert(NULL, "i'm %s\n", "dev_alert");dev_emerg(NULL, "i'm %s\n", "dev_emerg");return 0;
}static void __exit exit_my_module(void) {printk("Bye, my module!\n");
}module_init(init_my_module);
module_exit(exit_my_module);MODULE_LICENSE("GPL");
MODULE_AUTHOR("vec");