在kernel/sysctl.c 中有定义sysctl_init
int __init sysctl_init(void)
{
struct ctl_table_header *hdr;
hdr = register_sysctl_table(sysctl_base_table);
kmemleak_not_leak(hdr);
return 0;
}
这个函数会在proc/sys 目录下新建四个目录，这四个新建的目录是在sysctl_base_table 中有定义
static struct ctl_table sysctl_base_table[] = {
{
.procname = "kernel",
.mode = 0555,
.child = kern_table,
},
{
.procname = "vm",
.mode = 0555,
.child = vm_table,
},
{
.procname = "fs",
.mode = 0555,
.child = fs_table,
},
{
.procname = "debug",
.mode = 0555,
.child = debug_table,
},
{
.procname = "dev",
.mode = 0555,
.child = dev_table,
},
{ }
};
这四个目录下可以新建子目录或者新建文件，以kernel 这个目录为例
static struct ctl_table kern_table[] = {
{
.procname = "sched_child_runs_first",
.data = &sysctl_sched_child_runs_first,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = proc_dointvec,
},
}
通过cat 就可以读取或者echo就可以改变sched_child_runs_first 这个参数的值。从proc_dointvec 可以知道这个值是int类型的extern unsigned int sysctl_sched_child_runs_first;
如果想在自己的驱动中往proc/sys下面添加目录或者文件的话，可以参考下面在net目录下添加net/ipv4/route
static __net_init int sysctl_route_net_init(struct net *net)
{
struct ctl_table *tbl;
tbl = ipv4_route_flush_table;
if (!net_eq(net, &init_net)) {
tbl = kmemdup(tbl, sizeof(ipv4_route_flush_table), GFP_KERNEL);
if (!tbl)
goto err_dup;
/* Don't export sysctls to unprivileged users */
if (net->user_ns != &init_user_ns)
tbl[0].procname = NULL;
}
tbl[0].extra1 = net;
net->ipv4.route_hdr = register_net_sysctl(net, "net/ipv4/route", tbl);
if (!net->ipv4.route_hdr)
goto err_reg;
return 0;
err_reg:
if (tbl != ipv4_route_flush_table)
kfree(tbl);
err_dup:
return -ENOMEM;
}
那我们看看register_net_sysctl 是如何添加的呢？
struct ctl_table_header *register_net_sysctl(struct net *net,
const char *path, struct ctl_table *table)
{
//可以看到代表net device的struct net *net 有一个变量代表/proc/sys/net 这个sysctl的路径。第二个参数path 表示要插入的路径，第三个参数表示ctl_table *table
return __register_sysctl_table(&net->sysctls, path, table);
}
struct ctl_table_header *__register_sysctl_table(
struct ctl_table_set *set,
const char *path, struct ctl_table *table)
{
struct ctl_table_root *root = set->dir.header.root;
struct ctl_table_header *header;
const char *name, *nextname;
struct ctl_dir *dir;
struct ctl_table *entry;
struct ctl_node *node;
int nr_entries = 0;
for (entry = table; entry->procname; entry++)
nr_entries++;
header = kzalloc(sizeof(struct ctl_table_header) +
sizeof(struct ctl_node)*nr_entries, GFP_KERNEL);
if (!header)
return NULL;
node = (struct ctl_node *)(header + 1);
init_header(header, root, set, node, table);
if (sysctl_check_table(path, table))
goto fail;
spin_lock(&sysctl_lock);
dir = &set->dir;
/* Reference moved down the diretory tree get_subdir */
dir->header.nreg++;
spin_unlock(&sysctl_lock);
/* Find the directory for the ctl_table */
for (name = path; name; name = nextname) {
int namelen;
nextname = strchr(name, '/');
if (nextname) {
namelen = nextname - name;
nextname++;
} else {
namelen = strlen(name);
}
if (namelen == 0)
continue;
//找到需要插入的目录
dir = get_subdir(dir, name, namelen);
if (IS_ERR(dir))
goto fail;
}
spin_lock(&sysctl_lock);
//出入当前需要注册的ctl_table *table
if (insert_header(dir, header))
goto fail_put_dir_locked;
drop_sysctl_table(&dir->header);
spin_unlock(&sysctl_lock);
return header;
fail_put_dir_locked:
drop_sysctl_table(&dir->header);
spin_unlock(&sysctl_lock);
fail:
kfree(header);
dump_stack();
return NULL;
}
