/*
 *  inode.c - part of tracefs, a pseudo file system for activating tracing
 *
 * Based on debugfs by: Greg Kroah-Hartman <greg@kroah.com>
 *
 *  Copyright (C) 2014 Red Hat Inc, author: Steven Rostedt <srostedt@redhat.com>
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License version
 *      2 as published by the Free Software Foundation.
 *
 * tracefs is the file system that is used by the tracing infrastructure.
 *
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/kobject.h>
#include <linux/namei.h>
#include <linux/tracefs.h>
#include <linux/fsnotify.h>
#include <linux/seq_file.h>
#include <linux/parser.h>
#include <linux/magic.h>
#include <linux/slab.h>

#define TRACEFS_DEFAULT_MODE    0700

static struct vfsmount *tracefs_mount;
static int tracefs_mount_count;
static bool tracefs_registered;

static ssize_t default_read_file(struct file *file, char __user *buf,
                                 size_t count, loff_t *ppos)
{
        return 0;
}

static ssize_t default_write_file(struct file *file, const char __user *buf,
                                   size_t count, loff_t *ppos)
{
        return count;
}

static const struct file_operations tracefs_file_operations = {
        .read =         default_read_file,
        .write =        default_write_file,
        .open =         simple_open,
        .llseek =       noop_llseek,
};

static struct tracefs_dir_ops {
        int (*mkdir)(const char *name);
        int (*rmdir)(const char *name);
} tracefs_ops;

static char *get_dname(struct dentry *dentry)
{
        const char *dname;
        char *name;
        int len = dentry->d_name.len;

        dname = dentry->d_name.name;
        name = kmalloc(len + 1, GFP_KERNEL);
        if (!name)
                return NULL;
        memcpy(name, dname, len);
        name[len] = 0;
        return name;
}

static int tracefs_syscall_mkdir(struct inode *inode, struct dentry *dentry, umode_t mode)
{
        char *name;
        int ret;

        name = get_dname(dentry);
        if (!name)
                return -ENOMEM;

        /*
         * The mkdir call can call the generic functions that create
         * the files within the tracefs system. It is up to the individual
         * mkdir routine to handle races.
         */
        inode_unlock(inode);
        ret = tracefs_ops.mkdir(name);
        inode_lock(inode);

        kfree(name);

        return ret;
}

static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
{
        char *name;
        int ret;

        name = get_dname(dentry);
        if (!name)
                return -ENOMEM;

        /*
         * The rmdir call can call the generic functions that create
         * the files within the tracefs system. It is up to the individual
         * rmdir routine to handle races.
         * This time we need to unlock not only the parent (inode) but
         * also the directory that is being deleted.
         */
        inode_unlock(inode);
        inode_unlock(dentry->d_inode);

        ret = tracefs_ops.rmdir(name);

        inode_lock_nested(inode, I_MUTEX_PARENT);
        inode_lock(dentry->d_inode);

        kfree(name);

        return ret;
}

static const struct inode_operations tracefs_dir_inode_operations = {
        .lookup         = simple_lookup,
        .mkdir          = tracefs_syscall_mkdir,
        .rmdir          = tracefs_syscall_rmdir,
};

static struct inode *tracefs_get_inode(struct super_block *sb)
{
        struct inode *inode = new_inode(sb);
        if (inode) {
                inode->i_ino = get_next_ino();
                inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
        }
        return inode;
}

struct tracefs_mount_opts {
        kuid_t uid;
        kgid_t gid;
        umode_t mode;
};

enum {
        Opt_uid,
        Opt_gid,
        Opt_mode,
        Opt_err
};

static const match_table_t tokens = {
        {Opt_uid, "uid=%u"},
        {Opt_gid, "gid=%u"},
        {Opt_mode, "mode=%o"},
        {Opt_err, NULL}
};

struct tracefs_fs_info {
        struct tracefs_mount_opts mount_opts;
};

static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
{
        substring_t args[MAX_OPT_ARGS];
        int option;
        int token;
        kuid_t uid;
        kgid_t gid;
        char *p;

        opts->mode = TRACEFS_DEFAULT_MODE;

        while ((p = strsep(&data, ",")) != NULL) {
                if (!*p)
                        continue;

                token = match_token(p, tokens, args);
                switch (token) {
                case Opt_uid:
                        if (match_int(&args[0], &option))
                                return -EINVAL;
                        uid = make_kuid(current_user_ns(), option);
                        if (!uid_valid(uid))
                                return -EINVAL;
                        opts->uid = uid;
                        break;
                case Opt_gid:
                        if (match_int(&args[0], &option))
                                return -EINVAL;
                        gid = make_kgid(current_user_ns(), option);
                        if (!gid_valid(gid))
                                return -EINVAL;
                        opts->gid = gid;
                        break;
                case Opt_mode:
                        if (match_octal(&args[0], &option))
                                return -EINVAL;
                        opts->mode = option & S_IALLUGO;
                        break;
                /*
                 * We might like to report bad mount options here;
                 * but traditionally tracefs has ignored all mount options
                 */
                }
        }

        return 0;
}

static int tracefs_apply_options(struct super_block *sb)
{
        struct tracefs_fs_info *fsi = sb->s_fs_info;
        struct inode *inode = sb->s_root->d_inode;
        struct tracefs_mount_opts *opts = &fsi->mount_opts;

        inode->i_mode &= ~S_IALLUGO;
        inode->i_mode |= opts->mode;

        inode->i_uid = opts->uid;
        inode->i_gid = opts->gid;

        return 0;
}

static int tracefs_remount(struct super_block *sb, int *flags, char *data)
{
        int err;
        struct tracefs_fs_info *fsi = sb->s_fs_info;

        sync_filesystem(sb);
        err = tracefs_parse_options(data, &fsi->mount_opts);
        if (err)
                goto fail;

        tracefs_apply_options(sb);

fail:
        return err;
}

static int tracefs_show_options(struct seq_file *m, struct dentry *root)
{
        struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
        struct tracefs_mount_opts *opts = &fsi->mount_opts;

        if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
                seq_printf(m, ",uid=%u",
                           from_kuid_munged(&init_user_ns, opts->uid));
        if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
                seq_printf(m, ",gid=%u",
                           from_kgid_munged(&init_user_ns, opts->gid));
        if (opts->mode != TRACEFS_DEFAULT_MODE)
                seq_printf(m, ",mode=%o", opts->mode);

        return 0;
}

static const struct super_operations tracefs_super_operations = {
        .statfs         = simple_statfs,
        .remount_fs     = tracefs_remount,
        .show_options   = tracefs_show_options,
};

static int trace_fill_super(struct super_block *sb, void *data, int silent)
{
        static const struct tree_descr trace_files[] = {{""}};
        struct tracefs_fs_info *fsi;
        int err;

        fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
        sb->s_fs_info = fsi;
        if (!fsi) {
                err = -ENOMEM;
                goto fail;
        }

        err = tracefs_parse_options(data, &fsi->mount_opts);
        if (err)
                goto fail;

        err  =  simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
        if (err)
                goto fail;

        sb->s_op = &tracefs_super_operations;

        tracefs_apply_options(sb);

        return 0;

fail:
        kfree(fsi);
        sb->s_fs_info = NULL;
        return err;
}

static struct dentry *trace_mount(struct file_system_type *fs_type,
                        int flags, const char *dev_name,
                        void *data)
{
        return mount_single(fs_type, flags, data, trace_fill_super);
}

static struct file_system_type trace_fs_type = {
        .owner =        THIS_MODULE,
        .name =         "tracefs",
        .mount =        trace_mount,
        .kill_sb =      kill_litter_super,
};
MODULE_ALIAS_FS("tracefs");

static struct dentry *start_creating(const char *name, struct dentry *parent)
{
        struct dentry *dentry;
        int error;

        pr_debug("tracefs: creating file '%s'\n",name);

        error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
                              &tracefs_mount_count);
        if (error)
                return ERR_PTR(error);

        /* If the parent is not specified, we create it in the root.
         * We need the root dentry to do this, which is in the super
         * block. A pointer to that is in the struct vfsmount that we
         * have around.
         */
        if (!parent)
                parent = tracefs_mount->mnt_root;

        inode_lock(parent->d_inode);
        dentry = lookup_one_len(name, parent, strlen(name));
        if (!IS_ERR(dentry) && dentry->d_inode) {
                dput(dentry);
                dentry = ERR_PTR(-EEXIST);
        }

        if (IS_ERR(dentry)) {
                inode_unlock(parent->d_inode);
                simple_release_fs(&tracefs_mount, &tracefs_mount_count);
        }

        return dentry;
}

static struct dentry *failed_creating(struct dentry *dentry)
{
        inode_unlock(dentry->d_parent->d_inode);
        dput(dentry);
        simple_release_fs(&tracefs_mount, &tracefs_mount_count);
        return NULL;
}

static struct dentry *end_creating(struct dentry *dentry)
{
        inode_unlock(dentry->d_parent->d_inode);
        return dentry;
}

/**
 * tracefs_create_file - create a file in the tracefs filesystem
 * @name: a pointer to a string containing the name of the file to create.
 * @mode: the permission that the file should have.
 * @parent: a pointer to the parent dentry for this file.  This should be a
 *          directory dentry if set.  If this parameter is NULL, then the
 *          file will be created in the root of the tracefs filesystem.
 * @data: a pointer to something that the caller will want to get to later
 *        on.  The inode.i_private pointer will point to this value on
 *        the open() call.
 * @fops: a pointer to a struct file_operations that should be used for
 *        this file.
 *
 * This is the basic "create a file" function for tracefs.  It allows for a
 * wide range of flexibility in creating a file, or a directory (if you want
 * to create a directory, the tracefs_create_dir() function is
 * recommended to be used instead.)
 *
 * This function will return a pointer to a dentry if it succeeds.  This
 * pointer must be passed to the tracefs_remove() function when the file is
 * to be removed (no automatic cleanup happens if your module is unloaded,
 * you are responsible here.)  If an error occurs, %NULL will be returned.
 *
 * If tracefs is not enabled in the kernel, the value -%ENODEV will be
 * returned.
 */
struct dentry *tracefs_create_file(const char *name, umode_t mode,
                                   struct dentry *parent, void *data,
                                   const struct file_operations *fops)
{
        struct dentry *dentry;
        struct inode *inode;

        if (!(mode & S_IFMT))
                mode |= S_IFREG;
        BUG_ON(!S_ISREG(mode));
        dentry = start_creating(name, parent);

        if (IS_ERR(dentry))
                return NULL;

        inode = tracefs_get_inode(dentry->d_sb);
        if (unlikely(!inode))
                return failed_creating(dentry);

        inode->i_mode = mode;
        inode->i_fop = fops ? fops : &tracefs_file_operations;
        inode->i_private = data;
        d_instantiate(dentry, inode);
        fsnotify_create(dentry->d_parent->d_inode, dentry);
        return end_creating(dentry);
}

static struct dentry *__create_dir(const char *name, struct dentry *parent,
                                   const struct inode_operations *ops)
{
        struct dentry *dentry = start_creating(name, parent);
        struct inode *inode;

        if (IS_ERR(dentry))
                return NULL;

        inode = tracefs_get_inode(dentry->d_sb);
        if (unlikely(!inode))
                return failed_creating(dentry);

        inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
        inode->i_op = ops;
        inode->i_fop = &simple_dir_operations;

        /* directory inodes start off with i_nlink == 2 (for "." entry) */
        inc_nlink(inode);
        d_instantiate(dentry, inode);
        inc_nlink(dentry->d_parent->d_inode);
        fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
        return end_creating(dentry);
}

/**
 * tracefs_create_dir - create a directory in the tracefs filesystem
 * @name: a pointer to a string containing the name of the directory to
 *        create.
 * @parent: a pointer to the parent dentry for this file.  This should be a
 *          directory dentry if set.  If this parameter is NULL, then the
 *          directory will be created in the root of the tracefs filesystem.
 *
 * This function creates a directory in tracefs with the given name.
 *
 * This function will return a pointer to a dentry if it succeeds.  This
 * pointer must be passed to the tracefs_remove() function when the file is
 * to be removed. If an error occurs, %NULL will be returned.
 *
 * If tracing is not enabled in the kernel, the value -%ENODEV will be
 * returned.
 */
struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
{
        return __create_dir(name, parent, &simple_dir_inode_operations);
}

/**
 * tracefs_create_instance_dir - create the tracing instances directory
 * @name: The name of the instances directory to create
 * @parent: The parent directory that the instances directory will exist
 * @mkdir: The function to call when a mkdir is performed.
 * @rmdir: The function to call when a rmdir is performed.
 *
 * Only one instances directory is allowed.
 *
 * The instances directory is special as it allows for mkdir and rmdir to
 * to be done by userspace. When a mkdir or rmdir is performed, the inode
 * locks are released and the methhods passed in (@mkdir and @rmdir) are
 * called without locks and with the name of the directory being created
 * within the instances directory.
 *
 * Returns the dentry of the instances directory.
 */
struct dentry *tracefs_create_instance_dir(const char *name, struct dentry *parent,
                                          int (*mkdir)(const char *name),
                                          int (*rmdir)(const char *name))
{
        struct dentry *dentry;

        /* Only allow one instance of the instances directory. */
        if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))
                return NULL;

        dentry = __create_dir(name, parent, &tracefs_dir_inode_operations);
        if (!dentry)
                return NULL;

        tracefs_ops.mkdir = mkdir;
        tracefs_ops.rmdir = rmdir;

        return dentry;
}

static int __tracefs_remove(struct dentry *dentry, struct dentry *parent)
{
        int ret = 0;

        if (simple_positive(dentry)) {
                if (dentry->d_inode) {
                        dget(dentry);
                        switch (dentry->d_inode->i_mode & S_IFMT) {
                        case S_IFDIR:
                                ret = simple_rmdir(parent->d_inode, dentry);
                                break;
                        default:
                                simple_unlink(parent->d_inode, dentry);
                                break;
                        }
                        if (!ret)
                                d_delete(dentry);
                        dput(dentry);
                }
        }
        return ret;
}

/**
 * tracefs_remove - removes a file or directory from the tracefs filesystem
 * @dentry: a pointer to a the dentry of the file or directory to be
 *          removed.
 *
 * This function removes a file or directory in tracefs that was previously
 * created with a call to another tracefs function (like
 * tracefs_create_file() or variants thereof.)
 */
void tracefs_remove(struct dentry *dentry)
{
        struct dentry *parent;
        int ret;

        if (IS_ERR_OR_NULL(dentry))
                return;

        parent = dentry->d_parent;
        inode_lock(parent->d_inode);
        ret = __tracefs_remove(dentry, parent);
        inode_unlock(parent->d_inode);
        if (!ret)
                simple_release_fs(&tracefs_mount, &tracefs_mount_count);
}

/**
 * tracefs_remove_recursive - recursively removes a directory
 * @dentry: a pointer to a the dentry of the directory to be removed.
 *
 * This function recursively removes a directory tree in tracefs that
 * was previously created with a call to another tracefs function
 * (like tracefs_create_file() or variants thereof.)
 */
void tracefs_remove_recursive(struct dentry *dentry)
{
        struct dentry *child, *parent;

        if (IS_ERR_OR_NULL(dentry))
                return;

        parent = dentry;
 down:
        inode_lock(parent->d_inode);
 loop:
        /*
         * The parent->d_subdirs is protected by the d_lock. Outside that
         * lock, the child can be unlinked and set to be freed which can
         * use the d_u.d_child as the rcu head and corrupt this list.
         */
        spin_lock(&parent->d_lock);
        list_for_each_entry(child, &parent->d_subdirs, d_child) {
                if (!simple_positive(child))
                        continue;

                /* perhaps simple_empty(child) makes more sense */
                if (!list_empty(&child->d_subdirs)) {
                        spin_unlock(&parent->d_lock);
                        inode_unlock(parent->d_inode);
                        parent = child;
                        goto down;
                }

                spin_unlock(&parent->d_lock);

                if (!__tracefs_remove(child, parent))
                        simple_release_fs(&tracefs_mount, &tracefs_mount_count);

                /*
                 * The parent->d_lock protects agaist child from unlinking
                 * from d_subdirs. When releasing the parent->d_lock we can
                 * no longer trust that the next pointer is valid.
                 * Restart the loop. We'll skip this one with the
                 * simple_positive() check.
                 */
                goto loop;
        }
        spin_unlock(&parent->d_lock);

        inode_unlock(parent->d_inode);
        child = parent;
        parent = parent->d_parent;
        inode_lock(parent->d_inode);

        if (child != dentry)
                /* go up */
                goto loop;

        if (!__tracefs_remove(child, parent))
                simple_release_fs(&tracefs_mount, &tracefs_mount_count);
        inode_unlock(parent->d_inode);
}

/**
 * tracefs_initialized - Tells whether tracefs has been registered
 */
bool tracefs_initialized(void)
{
        return tracefs_registered;
}

static int __init tracefs_init(void)
{
        int retval;

        retval = sysfs_create_mount_point(kernel_kobj, "tracing");
        if (retval)
                return -EINVAL;

        retval = register_filesystem(&trace_fs_type);
        if (!retval)
                tracefs_registered = true;

        return retval;
}
core_initcall(tracefs_init);