control.c

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/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2008  Miklos Szeredi <[email protected]>

  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>

#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->f_path.dentry->d_inode->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) {
        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 = 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 uninitialized_var(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) {
            fc->max_background = val;
            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 = 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 uninitialized_var(val);
    ssize_t ret;

    ret = fuse_conn_limit_write(file, buf, count, ppos, &val,
                    max_user_congthresh);
    if (ret > 0) {
        struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
        if (fc) {
            fc->congestion_threshold = val;
            fuse_conn_put(fc);
        }
    }

    return ret;
}

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

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

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,
    .llseek = no_llseek,
};

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,
    .llseek = no_llseek,
};

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

    BUG_ON(fc->ctl_ndents >= FUSE_CTL_NUM_DENTRIES);
    dentry = d_alloc_name(parent, name);
    if (!dentry)
        return NULL;

    fc->ctl_dentry[fc->ctl_ndents++] = dentry;
    inode = new_inode(fuse_control_sb);
    if (!inode)
        return NULL;

    inode->i_ino = get_next_ino();
    inode->i_mode = mode;
    inode->i_uid = fc->user_id;
    inode->i_gid = fc->group_id;
    inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
    /* setting ->i_op to NULL is not allowed */
    if (iop)
        inode->i_op = iop;
    inode->i_fop = fop;
    set_nlink(inode, nlink);
    inode->i_private = fc;
    d_add(dentry, inode);
    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)
        return 0;

    parent = fuse_control_sb->s_root;
    inc_nlink(parent->d_inode);
    sprintf(name, "%u", fc->dev);
    parent = fuse_ctl_add_dentry(parent, fc, name, S_IFDIR | 0500, 2,
                     &simple_dir_inode_operations,
                     &simple_dir_operations);
    if (!parent)
        goto err;

    if (!fuse_ctl_add_dentry(parent, fc, "waiting", S_IFREG | 0400, 1,
                 NULL, &fuse_ctl_waiting_ops) ||
        !fuse_ctl_add_dentry(parent, fc, "abort", S_IFREG | 0200, 1,
                 NULL, &fuse_ctl_abort_ops) ||
        !fuse_ctl_add_dentry(parent, fc, "max_background", S_IFREG | 0600,
                 1, NULL, &fuse_conn_max_background_ops) ||
        !fuse_ctl_add_dentry(parent, fc, "congestion_threshold",
                 S_IFREG | 0600, 1, NULL,
                 &fuse_conn_congestion_threshold_ops))
        goto err;

    return 0;

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

/*
 * Remove a connection from the control filesystem (if it exists).
 * Caller must hold fuse_mutex
 */
void fuse_ctl_remove_conn(struct fuse_conn *fc)
{
    int i;

    if (!fuse_control_sb)
        return;

    for (i = fc->ctl_ndents - 1; i >= 0; i--) {
        struct dentry *dentry = fc->ctl_dentry[i];
        dentry->d_inode->i_private = NULL;
        d_drop(dentry);
        dput(dentry);
    }
    drop_nlink(fuse_control_sb->s_root->d_inode);
}

static int fuse_ctl_fill_super(struct super_block *sb, void *data, int silent)
{
    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 struct dentry *fuse_ctl_mount(struct file_system_type *fs_type,
            int flags, const char *dev_name, void *raw_data)
{
    return mount_single(fs_type, flags, raw_data, fuse_ctl_fill_super);
}

static void fuse_ctl_kill_sb(struct super_block *sb)
{
    struct fuse_conn *fc;

    mutex_lock(&fuse_mutex);
    fuse_control_sb = NULL;
    list_for_each_entry(fc, &fuse_conn_list, entry)
        fc->ctl_ndents = 0;
    mutex_unlock(&fuse_mutex);

    kill_litter_super(sb);
}

static struct file_system_type fuse_ctl_fs_type = {
    .owner      = THIS_MODULE,
    .name       = "fusectl",
    .mount      = fuse_ctl_mount,
    .kill_sb    = fuse_ctl_kill_sb,
};

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

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