original development tree for Linux kernel GTP module; now long in mainline.
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#include <linux/sched.h>
#include <linux/namei.h>
#include <linux/slab.h>
#include <linux/pid_namespace.h>
#include "internal.h"
/*
* /proc/self:
*/
static int proc_self_readlink(struct dentry *dentry, char __user *buffer,
int buflen)
{
struct pid_namespace *ns = dentry->d_sb->s_fs_info;
pid_t tgid = task_tgid_nr_ns(current, ns);
char tmp[PROC_NUMBUF];
if (!tgid)
return -ENOENT;
sprintf(tmp, "%d", tgid);
return vfs_readlink(dentry,buffer,buflen,tmp);
}
static void *proc_self_follow_link(struct dentry *dentry, struct nameidata *nd)
{
struct pid_namespace *ns = dentry->d_sb->s_fs_info;
pid_t tgid = task_tgid_nr_ns(current, ns);
char *name = ERR_PTR(-ENOENT);
if (tgid) {
/* 11 for max length of signed int in decimal + NULL term */
name = kmalloc(12, GFP_KERNEL);
if (!name)
name = ERR_PTR(-ENOMEM);
else
sprintf(name, "%d", tgid);
}
nd_set_link(nd, name);
return NULL;
}
static const struct inode_operations proc_self_inode_operations = {
.readlink = proc_self_readlink,
.follow_link = proc_self_follow_link,
.put_link = kfree_put_link,
};
static unsigned self_inum;
int proc_setup_self(struct super_block *s)
{
struct inode *root_inode = s->s_root->d_inode;
struct pid_namespace *ns = s->s_fs_info;
struct dentry *self;
mutex_lock(&root_inode->i_mutex);
self = d_alloc_name(s->s_root, "self");
if (self) {
struct inode *inode = new_inode_pseudo(s);
if (inode) {
inode->i_ino = self_inum;
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
inode->i_mode = S_IFLNK | S_IRWXUGO;
inode->i_uid = GLOBAL_ROOT_UID;
inode->i_gid = GLOBAL_ROOT_GID;
inode->i_op = &proc_self_inode_operations;
d_add(self, inode);
} else {
dput(self);
self = ERR_PTR(-ENOMEM);
}
} else {
self = ERR_PTR(-ENOMEM);
}
mutex_unlock(&root_inode->i_mutex);
if (IS_ERR(self)) {
pr_err("proc_fill_super: can't allocate /proc/self\n");
return PTR_ERR(self);
}
ns->proc_self = self;
return 0;
}
void __init proc_self_init(void)
{
proc_alloc_inum(&self_inum);
}