cuse.c

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/*
 * CUSE: Character device in Userspace
 *
 * Copyright (C) 2008-2009  SUSE Linux Products GmbH
 * Copyright (C) 2008-2009  Tejun Heo <[email protected]>
 *
 * This file is released under the GPLv2.
 *
 * CUSE enables character devices to be implemented from userland much
 * like FUSE allows filesystems.  On initialization /dev/cuse is
 * created.  By opening the file and replying to the CUSE_INIT request
 * userland CUSE server can create a character device.  After that the
 * operation is very similar to FUSE.
 *
 * A CUSE instance involves the following objects.
 *
 * cuse_conn    : contains fuse_conn and serves as bonding structure
 * channel  : file handle connected to the userland CUSE server
 * cdev     : the implemented character device
 * dev      : generic device for cdev
 *
 * Note that 'channel' is what 'dev' is in FUSE.  As CUSE deals with
 * devices, it's called 'channel' to reduce confusion.
 *
 * channel determines when the character device dies.  When channel is
 * closed, everything begins to destruct.  The cuse_conn is taken off
 * the lookup table preventing further access from cdev, cdev and
 * generic device are removed and the base reference of cuse_conn is
 * put.
 *
 * On each open, the matching cuse_conn is looked up and if found an
 * additional reference is taken which is released when the file is
 * closed.
 */

#include <linux/fuse.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/kthread.h>
#include <linux/list.h>
#include <linux/magic.h>
#include <linux/miscdevice.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/stat.h>
#include <linux/module.h>

#include "fuse_i.h"

#define CUSE_CONNTBL_LEN    64

struct cuse_conn {
    struct list_head    list;   /* linked on cuse_conntbl */
    struct fuse_conn    fc; /* fuse connection */
    struct cdev     *cdev;  /* associated character device */
    struct device       *dev;   /* device representing @cdev */

    /* init parameters, set once during initialization */
    bool            unrestricted_ioctl;
};

static DEFINE_SPINLOCK(cuse_lock);      /* protects cuse_conntbl */
static struct list_head cuse_conntbl[CUSE_CONNTBL_LEN];
static struct class *cuse_class;

static struct cuse_conn *fc_to_cc(struct fuse_conn *fc)
{
    return container_of(fc, struct cuse_conn, fc);
}

static struct list_head *cuse_conntbl_head(dev_t devt)
{
    return &cuse_conntbl[(MAJOR(devt) + MINOR(devt)) % CUSE_CONNTBL_LEN];
}


/**************************************************************************
 * CUSE frontend operations
 *
 * These are file operations for the character device.
 *
 * On open, CUSE opens a file from the FUSE mnt and stores it to
 * private_data of the open file.  All other ops call FUSE ops on the
 * FUSE file.
 */

static ssize_t cuse_read(struct file *file, char __user *buf, size_t count,
             loff_t *ppos)
{
    loff_t pos = 0;

    return fuse_direct_io(file, buf, count, &pos, 0);
}

static ssize_t cuse_write(struct file *file, const char __user *buf,
              size_t count, loff_t *ppos)
{
    loff_t pos = 0;
    /*
     * No locking or generic_write_checks(), the server is
     * responsible for locking and sanity checks.
     */
    return fuse_direct_io(file, buf, count, &pos, 1);
}

static int cuse_open(struct inode *inode, struct file *file)
{
    dev_t devt = inode->i_cdev->dev;
    struct cuse_conn *cc = NULL, *pos;
    int rc;

    /* look up and get the connection */
    spin_lock(&cuse_lock);
    list_for_each_entry(pos, cuse_conntbl_head(devt), list)
        if (pos->dev->devt == devt) {
            fuse_conn_get(&pos->fc);
            cc = pos;
            break;
        }
    spin_unlock(&cuse_lock);

    /* dead? */
    if (!cc)
        return -ENODEV;

    /*
     * Generic permission check is already done against the chrdev
     * file, proceed to open.
     */
    rc = fuse_do_open(&cc->fc, 0, file, 0);
    if (rc)
        fuse_conn_put(&cc->fc);
    return rc;
}

static int cuse_release(struct inode *inode, struct file *file)
{
    struct fuse_file *ff = file->private_data;
    struct fuse_conn *fc = ff->fc;

    fuse_sync_release(ff, file->f_flags);
    fuse_conn_put(fc);

    return 0;
}

static long cuse_file_ioctl(struct file *file, unsigned int cmd,
                unsigned long arg)
{
    struct fuse_file *ff = file->private_data;
    struct cuse_conn *cc = fc_to_cc(ff->fc);
    unsigned int flags = 0;

    if (cc->unrestricted_ioctl)
        flags |= FUSE_IOCTL_UNRESTRICTED;

    return fuse_do_ioctl(file, cmd, arg, flags);
}

static long cuse_file_compat_ioctl(struct file *file, unsigned int cmd,
                   unsigned long arg)
{
    struct fuse_file *ff = file->private_data;
    struct cuse_conn *cc = fc_to_cc(ff->fc);
    unsigned int flags = FUSE_IOCTL_COMPAT;

    if (cc->unrestricted_ioctl)
        flags |= FUSE_IOCTL_UNRESTRICTED;

    return fuse_do_ioctl(file, cmd, arg, flags);
}

static const struct file_operations cuse_frontend_fops = {
    .owner          = THIS_MODULE,
    .read           = cuse_read,
    .write          = cuse_write,
    .open           = cuse_open,
    .release        = cuse_release,
    .unlocked_ioctl     = cuse_file_ioctl,
    .compat_ioctl       = cuse_file_compat_ioctl,
    .poll           = fuse_file_poll,
    .llseek     = noop_llseek,
};


/**************************************************************************
 * CUSE channel initialization and destruction
 */

struct cuse_devinfo {
    const char      *name;
};

static int cuse_parse_one(char **pp, char *end, char **keyp, char **valp)
{
    char *p = *pp;
    char *key, *val;

    while (p < end && *p == '\0')
        p++;
    if (p == end)
        return 0;

    if (end[-1] != '\0') {
        printk(KERN_ERR "CUSE: info not properly terminated\n");
        return -EINVAL;
    }

    key = val = p;
    p += strlen(p);

    if (valp) {
        strsep(&val, "=");
        if (!val)
            val = key + strlen(key);
        key = strstrip(key);
        val = strstrip(val);
    } else
        key = strstrip(key);

    if (!strlen(key)) {
        printk(KERN_ERR "CUSE: zero length info key specified\n");
        return -EINVAL;
    }

    *pp = p;
    *keyp = key;
    if (valp)
        *valp = val;

    return 1;
}

static int cuse_parse_devinfo(char *p, size_t len, struct cuse_devinfo *devinfo)
{
    char *end = p + len;
    char *key, *val;
    int rc;

    while (true) {
        rc = cuse_parse_one(&p, end, &key, &val);
        if (rc < 0)
            return rc;
        if (!rc)
            break;
        if (strcmp(key, "DEVNAME") == 0)
            devinfo->name = val;
        else
            printk(KERN_WARNING "CUSE: unknown device info \"%s\"\n",
                   key);
    }

    if (!devinfo->name || !strlen(devinfo->name)) {
        printk(KERN_ERR "CUSE: DEVNAME unspecified\n");
        return -EINVAL;
    }

    return 0;
}

static void cuse_gendev_release(struct device *dev)
{
    kfree(dev);
}

static void cuse_process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
{
    struct cuse_conn *cc = fc_to_cc(fc);
    struct cuse_init_out *arg = req->out.args[0].value;
    struct page *page = req->pages[0];
    struct cuse_devinfo devinfo = { };
    struct device *dev;
    struct cdev *cdev;
    dev_t devt;
    int rc;

    if (req->out.h.error ||
        arg->major != FUSE_KERNEL_VERSION || arg->minor < 11) {
        goto err;
    }

    fc->minor = arg->minor;
    fc->max_read = max_t(unsigned, arg->max_read, 4096);
    fc->max_write = max_t(unsigned, arg->max_write, 4096);

    /* parse init reply */
    cc->unrestricted_ioctl = arg->flags & CUSE_UNRESTRICTED_IOCTL;

    rc = cuse_parse_devinfo(page_address(page), req->out.args[1].size,
                &devinfo);
    if (rc)
        goto err;

    /* determine and reserve devt */
    devt = MKDEV(arg->dev_major, arg->dev_minor);
    if (!MAJOR(devt))
        rc = alloc_chrdev_region(&devt, MINOR(devt), 1, devinfo.name);
    else
        rc = register_chrdev_region(devt, 1, devinfo.name);
    if (rc) {
        printk(KERN_ERR "CUSE: failed to register chrdev region\n");
        goto err;
    }

    /* devt determined, create device */
    rc = -ENOMEM;
    dev = kzalloc(sizeof(*dev), GFP_KERNEL);
    if (!dev)
        goto err_region;

    device_initialize(dev);
    dev_set_uevent_suppress(dev, 1);
    dev->class = cuse_class;
    dev->devt = devt;
    dev->release = cuse_gendev_release;
    dev_set_drvdata(dev, cc);
    dev_set_name(dev, "%s", devinfo.name);

    rc = device_add(dev);
    if (rc)
        goto err_device;

    /* register cdev */
    rc = -ENOMEM;
    cdev = cdev_alloc();
    if (!cdev)
        goto err_device;

    cdev->owner = THIS_MODULE;
    cdev->ops = &cuse_frontend_fops;

    rc = cdev_add(cdev, devt, 1);
    if (rc)
        goto err_cdev;

    cc->dev = dev;
    cc->cdev = cdev;

    /* make the device available */
    spin_lock(&cuse_lock);
    list_add(&cc->list, cuse_conntbl_head(devt));
    spin_unlock(&cuse_lock);

    /* announce device availability */
    dev_set_uevent_suppress(dev, 0);
    kobject_uevent(&dev->kobj, KOBJ_ADD);
out:
    kfree(arg);
    __free_page(page);
    return;

err_cdev:
    cdev_del(cdev);
err_device:
    put_device(dev);
err_region:
    unregister_chrdev_region(devt, 1);
err:
    fuse_conn_kill(fc);
    goto out;
}

static int cuse_send_init(struct cuse_conn *cc)
{
    int rc;
    struct fuse_req *req;
    struct page *page;
    struct fuse_conn *fc = &cc->fc;
    struct cuse_init_in *arg;
    void *outarg;

    BUILD_BUG_ON(CUSE_INIT_INFO_MAX > PAGE_SIZE);

    req = fuse_get_req(fc);
    if (IS_ERR(req)) {
        rc = PTR_ERR(req);
        goto err;
    }

    rc = -ENOMEM;
    page = alloc_page(GFP_KERNEL | __GFP_ZERO);
    if (!page)
        goto err_put_req;

    outarg = kzalloc(sizeof(struct cuse_init_out), GFP_KERNEL);
    if (!outarg)
        goto err_free_page;

    arg = &req->misc.cuse_init_in;
    arg->major = FUSE_KERNEL_VERSION;
    arg->minor = FUSE_KERNEL_MINOR_VERSION;
    arg->flags |= CUSE_UNRESTRICTED_IOCTL;
    req->in.h.opcode = CUSE_INIT;
    req->in.numargs = 1;
    req->in.args[0].size = sizeof(struct cuse_init_in);
    req->in.args[0].value = arg;
    req->out.numargs = 2;
    req->out.args[0].size = sizeof(struct cuse_init_out);
    req->out.args[0].value = outarg;
    req->out.args[1].size = CUSE_INIT_INFO_MAX;
    req->out.argvar = 1;
    req->out.argpages = 1;
    req->pages[0] = page;
    req->num_pages = 1;
    req->end = cuse_process_init_reply;
    fuse_request_send_background(fc, req);

    return 0;

err_free_page:
    __free_page(page);
err_put_req:
    fuse_put_request(fc, req);
err:
    return rc;
}

static void cuse_fc_release(struct fuse_conn *fc)
{
    struct cuse_conn *cc = fc_to_cc(fc);
    kfree(cc);
}

static int cuse_channel_open(struct inode *inode, struct file *file)
{
    struct cuse_conn *cc;
    int rc;

    /* set up cuse_conn */
    cc = kzalloc(sizeof(*cc), GFP_KERNEL);
    if (!cc)
        return -ENOMEM;

    fuse_conn_init(&cc->fc);

    INIT_LIST_HEAD(&cc->list);
    cc->fc.release = cuse_fc_release;

    cc->fc.connected = 1;
    cc->fc.blocked = 0;
    rc = cuse_send_init(cc);
    if (rc) {
        fuse_conn_put(&cc->fc);
        return rc;
    }
    file->private_data = &cc->fc;   /* channel owns base reference to cc */

    return 0;
}

static int cuse_channel_release(struct inode *inode, struct file *file)
{
    struct cuse_conn *cc = fc_to_cc(file->private_data);
    int rc;

    /* remove from the conntbl, no more access from this point on */
    spin_lock(&cuse_lock);
    list_del_init(&cc->list);
    spin_unlock(&cuse_lock);

    /* remove device */
    if (cc->dev)
        device_unregister(cc->dev);
    if (cc->cdev) {
        unregister_chrdev_region(cc->cdev->dev, 1);
        cdev_del(cc->cdev);
    }

    rc = fuse_dev_release(inode, file); /* puts the base reference */

    return rc;
}

static struct file_operations cuse_channel_fops; /* initialized during init */


/**************************************************************************
 * Misc stuff and module initializatiion
 *
 * CUSE exports the same set of attributes to sysfs as fusectl.
 */

static ssize_t cuse_class_waiting_show(struct device *dev,
                       struct device_attribute *attr, char *buf)
{
    struct cuse_conn *cc = dev_get_drvdata(dev);

    return sprintf(buf, "%d\n", atomic_read(&cc->fc.num_waiting));
}

static ssize_t cuse_class_abort_store(struct device *dev,
                      struct device_attribute *attr,
                      const char *buf, size_t count)
{
    struct cuse_conn *cc = dev_get_drvdata(dev);

    fuse_abort_conn(&cc->fc);
    return count;
}

static struct device_attribute cuse_class_dev_attrs[] = {
    __ATTR(waiting, S_IFREG | 0400, cuse_class_waiting_show, NULL),
    __ATTR(abort, S_IFREG | 0200, NULL, cuse_class_abort_store),
    { }
};

static struct miscdevice cuse_miscdev = {
    .minor      = MISC_DYNAMIC_MINOR,
    .name       = "cuse",
    .fops       = &cuse_channel_fops,
};

static int __init cuse_init(void)
{
    int i, rc;

    /* init conntbl */
    for (i = 0; i < CUSE_CONNTBL_LEN; i++)
        INIT_LIST_HEAD(&cuse_conntbl[i]);

    /* inherit and extend fuse_dev_operations */
    cuse_channel_fops       = fuse_dev_operations;
    cuse_channel_fops.owner     = THIS_MODULE;
    cuse_channel_fops.open      = cuse_channel_open;
    cuse_channel_fops.release   = cuse_channel_release;

    cuse_class = class_create(THIS_MODULE, "cuse");
    if (IS_ERR(cuse_class))
        return PTR_ERR(cuse_class);

    cuse_class->dev_attrs = cuse_class_dev_attrs;

    rc = misc_register(&cuse_miscdev);
    if (rc) {
        class_destroy(cuse_class);
        return rc;
    }

    return 0;
}

static void __exit cuse_exit(void)
{
    misc_deregister(&cuse_miscdev);
    class_destroy(cuse_class);
}

module_init(cuse_init);
module_exit(cuse_exit);

MODULE_AUTHOR("Tejun Heo <[email protected]>");
MODULE_DESCRIPTION("Character device in Userspace");
MODULE_LICENSE("GPL");