/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2008  Miklos Szeredi <miklos@szeredi.hu>

  This program can be distributed under the terms of the GNU GPL.
  See the file COPYING.
*/

#include "fuse_i.h"

#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs_context.h>
#include <linux/namei.h>

#define FUSE_CTL_SUPER_MAGIC 0x65735543

/*
 * This is non-NULL when the single instance of the control filesystem
 * exists.  Protected by fuse_mutex
 */
static struct super_block *fuse_control_sb;

static struct fuse_conn *fuse_ctl_file_conn_get(struct file *file)
{
        struct fuse_conn *fc;
        mutex_lock(&fuse_mutex);
        fc = file_inode(file)->i_private;
        if (fc)
                fc = fuse_conn_get(fc);
        mutex_unlock(&fuse_mutex);
        return fc;
}

static ssize_t fuse_conn_abort_write(struct file *file, const char __user *buf,
                                     size_t count, loff_t *ppos)
{
        struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
        if (fc) {
                if (fc->abort_err)
                        fc->aborted = true;
                fuse_abort_conn(fc);
                fuse_conn_put(fc);
        }
        return count;
}

static ssize_t fuse_conn_waiting_read(struct file *file, char __user *buf,
                                      size_t len, loff_t *ppos)
{
        char tmp[32];
        size_t size;

        if (!*ppos) {
                long value;
                struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
                if (!fc)
                        return 0;

                value = atomic_read(&fc->num_waiting);
                file->private_data = (void *)value;
                fuse_conn_put(fc);
        }
        size = sprintf(tmp, "%ld\n", (long)file->private_data);
        return simple_read_from_buffer(buf, len, ppos, tmp, size);
}

static ssize_t fuse_conn_limit_read(struct file *file, char __user *buf,
                                    size_t len, loff_t *ppos, unsigned val)
{
        char tmp[32];
        size_t size = sprintf(tmp, "%u\n", val);

        return simple_read_from_buffer(buf, len, ppos, tmp, size);
}

static ssize_t fuse_conn_limit_write(struct file *file, const char __user *buf,
                                     size_t count, loff_t *ppos, unsigned *val,
                                     unsigned global_limit)
{
        unsigned long t;
        unsigned limit = (1 << 16) - 1;
        int err;

        if (*ppos)
                return -EINVAL;

        err = kstrtoul_from_user(buf, count, 0, &t);
        if (err)
                return err;

        if (!capable(CAP_SYS_ADMIN))
                limit = min(limit, global_limit);

        if (t > limit)
                return -EINVAL;

        *val = t;

        return count;
}

static ssize_t fuse_conn_max_background_read(struct file *file,
                                             char __user *buf, size_t len,
                                             loff_t *ppos)
{
        struct fuse_conn *fc;
        unsigned val;

        fc = fuse_ctl_file_conn_get(file);
        if (!fc)
                return 0;

        val = READ_ONCE(fc->max_background);
        fuse_conn_put(fc);

        return fuse_conn_limit_read(file, buf, len, ppos, val);
}

static ssize_t fuse_conn_max_background_write(struct file *file,
                                              const char __user *buf,
                                              size_t count, loff_t *ppos)
{
        unsigned val;
        ssize_t ret;

        ret = fuse_conn_limit_write(file, buf, count, ppos, &val,
                                    max_user_bgreq);
        if (ret > 0) {
                struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
                if (fc) {
                        spin_lock(&fc->bg_lock);
                        fc->max_background = val;
                        fc->blocked = fc->num_background >= fc->max_background;
                        if (!fc->blocked)
                                wake_up(&fc->blocked_waitq);
                        spin_unlock(&fc->bg_lock);
                        fuse_conn_put(fc);
                }
        }

        return ret;
}

static ssize_t fuse_conn_congestion_threshold_read(struct file *file,
                                                   char __user *buf, size_t len,
                                                   loff_t *ppos)
{
        struct fuse_conn *fc;
        unsigned val;

        fc = fuse_ctl_file_conn_get(file);
        if (!fc)
                return 0;

        val = READ_ONCE(fc->congestion_threshold);
        fuse_conn_put(fc);

        return fuse_conn_limit_read(file, buf, len, ppos, val);
}

static ssize_t fuse_conn_congestion_threshold_write(struct file *file,
                                                    const char __user *buf,
                                                    size_t count, loff_t *ppos)
{
        unsigned val;
        struct fuse_conn *fc;
        ssize_t ret;

        ret = fuse_conn_limit_write(file, buf, count, ppos, &val,
                                    max_user_congthresh);
        if (ret <= 0)
                goto out;
        fc = fuse_ctl_file_conn_get(file);
        if (!fc)
                goto out;

        WRITE_ONCE(fc->congestion_threshold, val);
        fuse_conn_put(fc);
out:
        return ret;
}

static const struct file_operations fuse_ctl_abort_ops = {
        .open = nonseekable_open,
        .write = fuse_conn_abort_write,
};

static const struct file_operations fuse_ctl_waiting_ops = {
        .open = nonseekable_open,
        .read = fuse_conn_waiting_read,
};

static const struct file_operations fuse_conn_max_background_ops = {
        .open = nonseekable_open,
        .read = fuse_conn_max_background_read,
        .write = fuse_conn_max_background_write,
};

static const struct file_operations fuse_conn_congestion_threshold_ops = {
        .open = nonseekable_open,
        .read = fuse_conn_congestion_threshold_read,
        .write = fuse_conn_congestion_threshold_write,
};

static struct dentry *fuse_ctl_add_dentry(struct dentry *parent,
                                          struct fuse_conn *fc,
                                          const char *name, int mode,
                                          const struct inode_operations *iop,
                                          const struct file_operations *fop)
{
        struct dentry *dentry;
        struct inode *inode;

        dentry = d_alloc_name(parent, name);
        if (!dentry)
                return NULL;

        inode = new_inode(fuse_control_sb);
        if (!inode) {
                dput(dentry);
                return NULL;
        }

        inode->i_ino = get_next_ino();
        inode->i_mode = mode;
        inode->i_uid = fc->user_id;
        inode->i_gid = fc->group_id;
        simple_inode_init_ts(inode);
        /* setting ->i_op to NULL is not allowed */
        if (iop)
                inode->i_op = iop;
        inode->i_fop = fop;
        if (S_ISDIR(mode)) {
                inc_nlink(d_inode(parent));
                inc_nlink(inode);
        }
        inode->i_private = fc;
        d_make_persistent(dentry, inode);
        dput(dentry);

        /*
         * We are returning a borrowed reference here - it's only good while
         * fuse_mutex is held.  Actually it's d_make_persistent() return
         * value...
         */
        return dentry;
}

/*
 * Add a connection to the control filesystem (if it exists).  Caller
 * must hold fuse_mutex
 */
int fuse_ctl_add_conn(struct fuse_conn *fc)
{
        struct dentry *parent;
        char name[32];

        if (!fuse_control_sb || fc->no_control)
                return 0;

        parent = fuse_control_sb->s_root;
        sprintf(name, "%u", fc->dev);
        parent = fuse_ctl_add_dentry(parent, fc, name, S_IFDIR | 0500,
                                     &simple_dir_inode_operations,
                                     &simple_dir_operations);
        if (!parent)
                goto err;

        if (!fuse_ctl_add_dentry(parent, fc, "waiting", S_IFREG | 0400,
                                 NULL, &fuse_ctl_waiting_ops) ||
            !fuse_ctl_add_dentry(parent, fc, "abort", S_IFREG | 0200,
                                 NULL, &fuse_ctl_abort_ops) ||
            !fuse_ctl_add_dentry(parent, fc, "max_background", S_IFREG | 0600,
                                 NULL, &fuse_conn_max_background_ops) ||
            !fuse_ctl_add_dentry(parent, fc, "congestion_threshold",
                                 S_IFREG | 0600, NULL,
                                 &fuse_conn_congestion_threshold_ops))
                goto err;

        return 0;

 err:
        fuse_ctl_remove_conn(fc);
        return -ENOMEM;
}

static void remove_one(struct dentry *dentry)
{
        d_inode(dentry)->i_private = NULL;
}

/*
 * Remove a connection from the control filesystem (if it exists).
 * Caller must hold fuse_mutex
 */
void fuse_ctl_remove_conn(struct fuse_conn *fc)
{
        char name[32];

        if (!fuse_control_sb || fc->no_control)
                return;

        sprintf(name, "%u", fc->dev);
        simple_remove_by_name(fuse_control_sb->s_root, name, remove_one);
}

static int fuse_ctl_fill_super(struct super_block *sb, struct fs_context *fsc)
{
        static const struct tree_descr empty_descr = {""};
        struct fuse_conn *fc;
        int err;

        err = simple_fill_super(sb, FUSE_CTL_SUPER_MAGIC, &empty_descr);
        if (err)
                return err;

        mutex_lock(&fuse_mutex);
        BUG_ON(fuse_control_sb);
        fuse_control_sb = sb;
        list_for_each_entry(fc, &fuse_conn_list, entry) {
                err = fuse_ctl_add_conn(fc);
                if (err) {
                        fuse_control_sb = NULL;
                        mutex_unlock(&fuse_mutex);
                        return err;
                }
        }
        mutex_unlock(&fuse_mutex);

        return 0;
}

static int fuse_ctl_get_tree(struct fs_context *fsc)
{
        return get_tree_single(fsc, fuse_ctl_fill_super);
}

static const struct fs_context_operations fuse_ctl_context_ops = {
        .get_tree       = fuse_ctl_get_tree,
};

static int fuse_ctl_init_fs_context(struct fs_context *fsc)
{
        fsc->ops = &fuse_ctl_context_ops;
        return 0;
}

static void fuse_ctl_kill_sb(struct super_block *sb)
{
        mutex_lock(&fuse_mutex);
        fuse_control_sb = NULL;
        mutex_unlock(&fuse_mutex);

        kill_anon_super(sb);
}

static struct file_system_type fuse_ctl_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "fusectl",
        .init_fs_context = fuse_ctl_init_fs_context,
        .kill_sb        = fuse_ctl_kill_sb,
};
MODULE_ALIAS_FS("fusectl");

int __init fuse_ctl_init(void)
{
        return register_filesystem(&fuse_ctl_fs_type);
}

void __exit fuse_ctl_cleanup(void)
{
        unregister_filesystem(&fuse_ctl_fs_type);
}