// SPDX-License-Identifier: GPL-2.0
#include <linux/cache.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/pid_namespace.h>
#include "internal.h"

/*
 * /proc/thread_self:
 */
static const char *proc_thread_self_get_link(struct dentry *dentry,
                                             struct inode *inode,
                                             struct delayed_call *done)
{
        struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
        pid_t tgid = task_tgid_nr_ns(current, ns);
        pid_t pid = task_pid_nr_ns(current, ns);
        char *name;

        if (!pid)
                return ERR_PTR(-ENOENT);
        name = kmalloc(10 + 6 + 10 + 1, dentry ? GFP_KERNEL : GFP_ATOMIC);
        if (unlikely(!name))
                return dentry ? ERR_PTR(-ENOMEM) : ERR_PTR(-ECHILD);
        sprintf(name, "%u/task/%u", tgid, pid);
        set_delayed_call(done, kfree_link, name);
        return name;
}

static const struct inode_operations proc_thread_self_inode_operations = {
        .get_link       = proc_thread_self_get_link,
};

unsigned thread_self_inum __ro_after_init;

int proc_setup_thread_self(struct super_block *s)
{
        struct inode *root_inode = d_inode(s->s_root);
        struct dentry *thread_self;
        int ret = -ENOMEM;

        inode_lock(root_inode);
        thread_self = d_alloc_name(s->s_root, "thread-self");
        if (thread_self) {
                struct inode *inode = new_inode(s);
                if (inode) {
                        inode->i_ino = thread_self_inum;
                        simple_inode_init_ts(inode);
                        inode->i_mode = S_IFLNK | S_IRWXUGO;
                        inode->i_uid = GLOBAL_ROOT_UID;
                        inode->i_gid = GLOBAL_ROOT_GID;
                        inode->i_op = &proc_thread_self_inode_operations;
                        d_make_persistent(thread_self, inode);
                        ret = 0;
                }
                dput(thread_self);
        }
        inode_unlock(root_inode);

        if (ret)
                pr_err("proc_fill_super: can't allocate /proc/thread-self\n");
        return ret;
}

void __init proc_thread_self_init(void)
{
        proc_alloc_inum(&thread_self_inum);
}