sysctl使用方法的变化

内核版本：3.6

Author：zhangskd @ csdn blog

Change

在v3.4中包含一个patch，提交者Eric W. Biederman描述如下：

Rewrite of sysctl for speed and charity.

Insert/remove/Lookup in sysctl are now O(NlogN) operations, and are no longer bottlenecks in the

process of adding and removing network devices.

sysctl is now focused on being a filesystem instead of system call and the code can be found in

fs/proc/proc_sysctl.c. Hopefully this means the code is now approachable.

可见sysctl的实现发生了较大的变化。

但是这对sysctl的使用有什么影响呢？再来看另一个相关patch：

sysctl: Add register_sysctl for normal sysctl users

The plan is to convert all callers of register_sysctl_table and register_sysctl_paths to register_sysctl.

The interface to register_sysctl is enough nicer. This should make the callers a bit more readable.

Additionally after the conversion the 230 lines of backwards compatibility can be removed.

可见sysctl的注册函数发生了变化，现在是：

[java] view plaincopyprint?

1. /**
2. * register_sysctl - register a sysctl table
3. * @path: The path to the directory the sysctl table is in.
4. * @table: the table structure
5. *
6. * Register a sysctl table. @table should be a filled in ctl_table array.
7. * A completely 0 filled entry terminates the table.
8. *
9. * See __register_sysctl_table for more details.
10. */
12. struct ctl_table_header *register_sysctl (const char *path, struct ctl_table *table);

/** * register_sysctl - register a sysctl table * @path: The path to the directory the sysctl table is in. * @table: the table structure * * Register a sysctl table. @table should be a filled in ctl_table array. * A completely 0 filled entry terminates the table. * * See __register_sysctl_table for more details. */struct ctl_table_header *register_sysctl (const char *path, struct ctl_table *table);

之前的注册函数为：

[java] view plaincopyprint?

1. struct ctl_table_header *register_sysctl_table (struct ctl_table *table);

struct ctl_table_header *register_sysctl_table (struct ctl_table *table);

也就是说现在可以通过注册函数来指定注册的路径，更加方便了。

注销函数不变：

[java] view plaincopyprint?

1. /**
2. * unregister_sysctl_table - unregister a sysctl table hierarchy
3. * @header: the header returned from register_sysctl_table
4. *
5. * Unregisters the sysctl table and all children. proc entires may not actually
6. * be removed until they are no longer used by anyone.
7. */
8. void unregister_sysctl_table (struct ctl_table_header *header);

/** * unregister_sysctl_table - unregister a sysctl table hierarchy * @header: the header returned from register_sysctl_table * * Unregisters the sysctl table and all children. proc entires may not actually * be removed until they are no longer used by anyone. */void unregister_sysctl_table (struct ctl_table_header *header);

structure

现在的ctl_table：

@include/linux/sysctl.h

[java] view plaincopyprint?

1. /* A sysctl table is an array of struct ctl_table: */
2. struct ctl_table
3. {
4. const char *procname;/* Text ID for /proc/sys, or zero，文件名 */
5. void * data;
6. int maxlen;
7. umode_t mode;
8. struct ctl_table *child; /* Deprecated */
9. proc_handler *proc_handler; /* Callback for text formatting，读写操作函数 */
10. struct ctl_table_poll *poll;
11. void *extra1; /* 变量的最小值min */
12. void *extra2; /* 变量的最大值max */
13. }

/* A sysctl table is an array of struct ctl_table: */struct ctl_table{    const char *procname; /* Text ID for /proc/sys, or zero，文件名 */    void * data;    int maxlen;    umode_t mode;    struct ctl_table *child; /* Deprecated */    proc_handler *proc_handler; /* Callback for text formatting，读写操作函数 */    struct ctl_table_poll *poll;    void *extra1; /*  变量的最小值min */    void *extra2; /* 变量的最大值max */}

proc_handler的常用取值：

proc_dointvec /* 读写一个包含一个或多个整数的数组*/

proc_dostring /* 读写一个字符串*/

proc_dointvec_minmax /* 写的数组必须在min~max范围内*/

一个instance：

@net/ipv4/sysctl_net_ipv4.c

[java] view plaincopyprint?

1. static struct ctl_table ipv4_table[] = {
2. ...
3. {
4. .procname = "tcp_congestion_control",
5. .mode = 0644;
6. .maxlen = TCP_CA_NAME_MAX,
7. .proc_handler = proc_tcp_congestion_control,
8. },
9. ...
10. {
11. .procname = "tcp_early_retrans",
12. .data = &sysctl_tcp_early_retrans,
13. .maxlen = sizeof(int),
14. .mode = 0644,
15. .proc_handler = proc_dointvec_minmax,
16. .extra1 = &zero,
17. .extra2 = &two,
18. },
19. ...
20. };

static struct ctl_table ipv4_table[] = {    ...    {        .procname = "tcp_congestion_control",        .mode = 0644;        .maxlen = TCP_CA_NAME_MAX,        .proc_handler = proc_tcp_congestion_control,    },    ...    {        .procname = "tcp_early_retrans",        .data = &sysctl_tcp_early_retrans,        .maxlen = sizeof(int),        .mode = 0644,        .proc_handler = proc_dointvec_minmax,        .extra1 = &zero,        .extra2 = &two,    },    ...};

这些选项的简要说明在：Documentation/networking/ipv4/*

这些选项的定义在：net/ipv4/tcp_input.c

command

sysctl — configure kernel parameters at runtime

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.

使用：

sysctl net.ipv4.tcp_congestion_control // read

sysctl -w net.ipv4.tcp_congestion_control = "cubic" // write

example

这是新的使用方法示例：

[java] view plaincopyprint?

1. #include <linux/init.h>
2. #include <linux/module.h>
3. #include <linux/sysctl.h>
4. #include <linux/kernel.h>
6. static char path[] ="net/test";
7. static int zero =0;
8. static int two = 2;
9. int sysctl_tcp_new;
11. static struct ctl_table_header *header;
13. static struct ctl_table new[] = {
14. {
15. .procname = "tcp_new",
16. .data = &sysctl_tcp_new,
17. .maxlen = sizeof(int),
18. .mode = 0644,
19. .proc_handler = proc_dointvec_minmax,
20. .extra1 = &zero,
21. .extra2 = &two
22. },
23. { }
24. };
26. static int __init sysctl_module_init(void)
27. {
28. header = register_sysctl(path, new);
29. if(!header) {
30. printk(KERN_ERR"register_sysctl() failed.\n");
31. return -1;
32. }
33. return 0;
34. }
36. static void __exit sysctl_module_exit(void)
37. {
38. if(header)
39. unregister_sysctl_table(header);
40. }
42. module_init(sysctl_module_init);
43. module_exit(sysctl_module_exit);
44. MODULE_AUTHOR("zhangsk");
45. MODULE_LICENSE("GPL");

#include <linux/init.h>#include <linux/module.h>#include <linux/sysctl.h>#include <linux/kernel.h>static char path[] = "net/test";static int zero = 0;static int two = 2;int sysctl_tcp_new;static struct ctl_table_header *header;static struct ctl_table new[] = {{.procname = "tcp_new",.data = &sysctl_tcp_new,.maxlen = sizeof(int),.mode = 0644,.proc_handler = proc_dointvec_minmax,.extra1 = &zero,.extra2 = &two},{ }};static int __init sysctl_module_init(void){header = register_sysctl(path, new);if(!header) {printk(KERN_ERR"register_sysctl() failed.\n");return -1;}return 0;}static void __exit sysctl_module_exit(void){if(header)unregister_sysctl_table(header);}module_init(sysctl_module_init);module_exit(sysctl_module_exit);MODULE_AUTHOR("zhangsk");MODULE_LICENSE("GPL");

模块加载时，就自动创建目录/proc/sys/net/test/，并在其下创建文件tcp_new，取值可为0、1或2。

模块卸载时，此目录则会被删除，当然这是在没人使用了之后。

这是旧的使用方法示例：

[java] view plaincopyprint?

1. #include <linux/init.h>
2. #include <linux/module.h>
3. #include <linux/sysctl.h>
5. static int zero =0;
6. static int two = 2;
7. int sysctl_tcp_new;
9. static struct ctl_table_header *header;
11. static struct ctl_table my_table[] = {
12. {
13. .procname = "tcp_new",
14. .data = &sysctl_tcp_new,
15. .maxlen = sizeof(int),
16. .mode = 0644,
17. .proc_handler = proc_dointvec_minmax,
18. .extra1 = &zero,
19. .extra2 = &two, },
20. {},
21. };
23. static struct ctl_table test_dir_table[] = {
24. {
25. .procname = "test",
26. .mode = 0555,
27. .child = my_table,
28. },
29. {},
30. };
32. static struct ctl_table net_dir_table[] = {
33. {
34. .procname = "net",
35. .mode = 0555,
36. .child = test_dir_table,
37. },
38. {},
39. };
41. static int __init sysctl_module_init(void)
42. {
43. header = register_sysctl_table(net_dir_table);
44. if(!header) {
45. printk(KERN_ERR"register_sysctl_table() failed.\n");
46. return -1;
47. }
48. return 0;
49. }
51. static void __exit sysctl_module_exit(void)
52. {
53. if(header)
54. unregister_sysctl_table(header);
55. }
57. module_init(sysctl_module_init);
58. module_exit(sysctl_module_exit);
59. MODULE_AUTHOR("zhangsk");
60. MODULE_LICENSE("GPL");

转载地址：http://blog.csdn.net/zhangskd/article/details/8447277

#include <linux/init.h>#include <linux/module.h>#include <linux/sysctl.h>static int zero = 0;static int two = 2;int sysctl_tcp_new;static struct ctl_table_header *header;static struct ctl_table my_table[] = {        {                .procname = "tcp_new",                .data = &sysctl_tcp_new,                .maxlen = sizeof(int),                .mode = 0644,                .proc_handler = proc_dointvec_minmax,                .extra1 = &zero,                .extra2 = &two, },        {},};static struct ctl_table test_dir_table[] = {        {                .procname = "test",                .mode = 0555,                .child = my_table,        },        {},};static struct ctl_table net_dir_table[] = {        {                .procname = "net",                .mode = 0555,                .child = test_dir_table,        },        {},};static int __init sysctl_module_init(void){        header = register_sysctl_table(net_dir_table);        if(!header) {                printk(KERN_ERR"register_sysctl_table() failed.\n");                return -1;        }        return 0;}static void __exit sysctl_module_exit(void){        if(header)                unregister_sysctl_table(header);}module_init(sysctl_module_init);module_exit(sysctl_module_exit);MODULE_AUTHOR("zhangsk");MODULE_LICENSE("GPL");