On Mon, May 22, 2017 at 09:09:42PM +0100, Sean Young wrote:
>On Mon, May 01, 2017 at 06:04:42PM +0200, David Härdeman wrote:
>> Using the kernel ida facilities, we can avoid a lot of unnecessary code and at the same
>> time get rid of lirc_dev_lock in favour of per-device locks (the irctls array was used
>> throughout lirc_dev so this patch necessarily touches a lot of code).
>>
>> Signed-off-by: David Härdeman <david@xxxxxxxxxxx>
>> ---
>> drivers/media/rc/ir-lirc-codec.c | 9 -
>> drivers/media/rc/lirc_dev.c | 258 ++++++++++++-------------------
>> drivers/staging/media/lirc/lirc_zilog.c | 16 +-
>> include/media/lirc_dev.h | 14 --
>> 4 files changed, 115 insertions(+), 182 deletions(-)
>>
>> diff --git a/drivers/media/rc/ir-lirc-codec.c b/drivers/media/rc/ir-lirc-codec.c
>> index a30af91710fe..2c1221a61ea1 100644
>> --- a/drivers/media/rc/ir-lirc-codec.c
>> +++ b/drivers/media/rc/ir-lirc-codec.c
>> @@ -382,7 +382,6 @@ static int ir_lirc_register(struct rc_dev *dev)
>>
>> snprintf(drv->name, sizeof(drv->name), "ir-lirc-codec (%s)",
>> dev->driver_name);
>> - drv->minor = -1;
>> drv->features = features;
>> drv->data = &dev->raw->lirc;
>> drv->rbuf = NULL;
>> @@ -394,11 +393,9 @@ static int ir_lirc_register(struct rc_dev *dev)
>> drv->rdev = dev;
>> drv->owner = THIS_MODULE;
>>
>> - drv->minor = lirc_register_driver(drv);
>> - if (drv->minor < 0) {
>> - rc = -ENODEV;
>> + rc = lirc_register_driver(drv);
>> + if (rc < 0)
>> goto out;
>> - }
>>
>> dev->raw->lirc.drv = drv;
>> dev->raw->lirc.dev = dev;
>> @@ -413,7 +410,7 @@ static int ir_lirc_unregister(struct rc_dev *dev)
>> {
>> struct lirc_codec *lirc = &dev->raw->lirc;
>>
>> - lirc_unregister_driver(lirc->drv->minor);
>> + lirc_unregister_driver(lirc->drv);
>> kfree(lirc->drv);
>> lirc->drv = NULL;
>>
>> diff --git a/drivers/media/rc/lirc_dev.c b/drivers/media/rc/lirc_dev.c
>> index e44e0b23b883..7db7d4c57991 100644
>> --- a/drivers/media/rc/lirc_dev.c
>> +++ b/drivers/media/rc/lirc_dev.c
>> @@ -31,23 +31,35 @@
>> #include <linux/bitops.h>
>> #include <linux/device.h>
>> #include <linux/cdev.h>
>> +#include <linux/idr.h>
>>
>> #include <media/rc-core.h>
>> #include <media/lirc.h>
>> #include <media/lirc_dev.h>
>>
>> #define IRCTL_DEV_NAME "BaseRemoteCtl"
>> -#define NOPLUG -1
>> #define LOGHEAD "lirc_dev (%s[%d]): "
>>
>> static dev_t lirc_base_dev;
>>
>> +/**
>> + * struct irctl - lirc per-device structure
>> + * @d: internal copy of the &struct lirc_driver for the device
>> + * @dead: if the device has gone away
>> + * @users: the number of users of the lirc chardev (currently limited to 1)
>> + * @mutex: synchronizes open()/close()/ioctl()/etc calls
>> + * @buf: used to store lirc RX data
>> + * @buf_internal: whether @buf was allocated internally or not
>> + * @chunk_size: @buf stores and read() returns data chunks of this size
>> + * @dev: the &struct device for the lirc device
>> + * @cdev: the &struct device for the lirc chardev
>> + */
>> struct irctl {
>> struct lirc_driver d;
>> - int attached;
>> - int open;
>> + bool dead;
>> + unsigned users;
>>
>> - struct mutex irctl_lock;
>> + struct mutex mutex;
>> struct lirc_buffer *buf;
>> bool buf_internal;
>> unsigned int chunk_size;
>> @@ -56,9 +68,9 @@ struct irctl {
>> struct cdev cdev;
>> };
>>
>> -static DEFINE_MUTEX(lirc_dev_lock);
>> -
>> -static struct irctl *irctls[MAX_IRCTL_DEVICES];
>> +/* Used to keep track of allocated lirc devices */
>> +#define LIRC_MAX_DEVICES 256
>> +static DEFINE_IDA(lirc_ida);
>>
>> /* Only used for sysfs but defined to void otherwise */
>> static struct class *lirc_class;
>> @@ -72,9 +84,6 @@ static void lirc_release(struct device *ld)
>> kfree(ir->buf);
>> }
>>
>> - mutex_lock(&lirc_dev_lock);
>> - irctls[ir->d.minor] = NULL;
>> - mutex_unlock(&lirc_dev_lock);
>> kfree(ir);
>> }
>>
>> @@ -117,7 +126,18 @@ static int lirc_allocate_buffer(struct irctl *ir)
>> return err;
>> }
>>
>> -int lirc_register_driver(struct lirc_driver *d)
>> +/**
>> + * lirc_register_driver() - create a new lirc device by registering a driver
>> + * @d: the &struct lirc_driver to register
>> + *
>> + * This function allocates and registers a lirc device for a given
>> + * &lirc_driver. The &lirc_driver structure is updated to contain
>> + * information about the allocated device (minor, buffer, etc).
>> + *
>> + * Return: zero on success or a negative error value.
>> + */
>> +int
>> +lirc_register_driver(struct lirc_driver *d)
>> {
>> struct irctl *ir;
>> int minor;
>> @@ -138,12 +158,6 @@ int lirc_register_driver(struct lirc_driver *d)
>> return -EINVAL;
>> }
>>
>> - if (d->minor >= MAX_IRCTL_DEVICES) {
>> - dev_err(d->dev, "minor must be between 0 and %d!\n",
>> - MAX_IRCTL_DEVICES - 1);
>> - return -EBADRQC;
>> - }
>> -
>> if (d->code_length < 1 || d->code_length > (BUFLEN * 8)) {
>> dev_err(d->dev, "code length must be less than %d bits\n",
>> BUFLEN * 8);
>> @@ -156,49 +170,30 @@ int lirc_register_driver(struct lirc_driver *d)
>> return -EBADRQC;
>> }
>>
>> - mutex_lock(&lirc_dev_lock);
>> -
>> - minor = d->minor;
>> + d->name[sizeof(d->name)-1] = '\0';
>> + if (d->features == 0)
>> + d->features = LIRC_CAN_REC_LIRCCODE;
>>
>> - if (minor < 0) {
>> - /* find first free slot for driver */
>> - for (minor = 0; minor < MAX_IRCTL_DEVICES; minor++)
>> - if (!irctls[minor])
>> - break;
>> - if (minor == MAX_IRCTL_DEVICES) {
>> - dev_err(d->dev, "no free slots for drivers!\n");
>> - err = -ENOMEM;
>> - goto out_lock;
>> - }
>> - } else if (irctls[minor]) {
>> - dev_err(d->dev, "minor (%d) just registered!\n", minor);
>> - err = -EBUSY;
>> - goto out_lock;
>> - }
>> + minor = ida_simple_get(&lirc_ida, 0, LIRC_MAX_DEVICES, GFP_KERNEL);
>> + if (minor < 0)
>> + return minor;
>> + d->minor = minor;
>>
>> ir = kzalloc(sizeof(struct irctl), GFP_KERNEL);
>> if (!ir) {
>> err = -ENOMEM;
>> - goto out_lock;
>> + goto out_minor;
>> }
>>
>> - mutex_init(&ir->irctl_lock);
>> - irctls[minor] = ir;
>> - d->minor = minor;
>> -
>> - /* some safety check 8-) */
>> - d->name[sizeof(d->name)-1] = '\0';
>> -
>> - if (d->features == 0)
>> - d->features = LIRC_CAN_REC_LIRCCODE;
>> + mutex_init(&ir->mutex);
>>
>> ir->d = *d;
>
>Here we copy lirc_driver.
>
>>
>> if (LIRC_CAN_REC(d->features)) {
>> - err = lirc_allocate_buffer(irctls[minor]);
>> + err = lirc_allocate_buffer(ir);
>> if (err) {
>> kfree(ir);
>> - goto out_lock;
>> + goto out_minor;
>> }
>> d->rbuf = ir->buf;
>> }
>> @@ -218,107 +213,82 @@ int lirc_register_driver(struct lirc_driver *d)
>> if (err)
>> goto out_free_dev;
>>
>> - ir->attached = 1;
>> -
>> err = device_add(&ir->dev);
>> if (err)
>> goto out_cdev;
>>
>> - mutex_unlock(&lirc_dev_lock);
>> -
>> dev_info(ir->d.dev, "lirc_dev: driver %s registered at minor = %d\n",
>> ir->d.name, ir->d.minor);
>>
>> - return minor;
>> + d->lirc_internal = ir;
>
>And now a store a pointer to the copy in the original lirc_driver.
>
>It would be much better to not copy lirc_driver and the lirc_internal
>member would be unnecessary.
I know, but this is a more minimal fix. The struct copy is already in
the current code and I'd prefer removing it in a separate patch once the
use of lirc_driver has been vetted.
>> + return 0;
>>
>> out_cdev:
>> cdev_del(&ir->cdev);
>> out_free_dev:
>> put_device(&ir->dev);
>> -out_lock:
>> - mutex_unlock(&lirc_dev_lock);
>> +out_minor:
>> + ida_simple_remove(&lirc_ida, minor);
>>
>> return err;
>> }
>> EXPORT_SYMBOL(lirc_register_driver);
>>
>> -int lirc_unregister_driver(int minor)
>> +/**
>> + * lirc_unregister_driver() - remove the lirc device for a given driver
>> + * @d: the &struct lirc_driver to unregister
>> + *
>> + * This function unregisters the lirc device for a given &lirc_driver.
>> + */
>> +void
>> +lirc_unregister_driver(struct lirc_driver *d)
>> {
>> struct irctl *ir;
>>
>> - if (minor < 0 || minor >= MAX_IRCTL_DEVICES) {
>> - pr_err("minor (%d) must be between 0 and %d!\n",
>> - minor, MAX_IRCTL_DEVICES - 1);
>> - return -EBADRQC;
>> - }
>> + if (!d->lirc_internal)
>> + return;
>>
>> - ir = irctls[minor];
>> - if (!ir) {
>> - pr_err("failed to get irctl\n");
>> - return -ENOENT;
>> - }
>> + ir = d->lirc_internal;
>
>This is done to find a our copy again.
>
>> - mutex_lock(&lirc_dev_lock);
>> -
>> - if (ir->d.minor != minor) {
>> - dev_err(ir->d.dev, "lirc_dev: minor %d device not registered\n",
>> - minor);
>> - mutex_unlock(&lirc_dev_lock);
>> - return -ENOENT;
>> - }
>> + mutex_lock(&ir->mutex);
>>
>> dev_dbg(ir->d.dev, "lirc_dev: driver %s unregistered from minor = %d\n",
>> ir->d.name, ir->d.minor);
>>
>> - ir->attached = 0;
>> - if (ir->open) {
>> + ir->dead = true;
>> + if (ir->users) {
>> dev_dbg(ir->d.dev, LOGHEAD "releasing opened driver\n",
>> ir->d.name, ir->d.minor);
>> wake_up_interruptible(&ir->buf->wait_poll);
>> }
>>
>> - mutex_unlock(&lirc_dev_lock);
>> + mutex_unlock(&ir->mutex);
>>
>> device_del(&ir->dev);
>> cdev_del(&ir->cdev);
>> - put_device(&ir->dev);
>> -
>> - return 0;
>> + ida_simple_remove(&lirc_ida, d->minor);
>> + d->minor = -1;
>> + d->lirc_internal = NULL;
>> }
>> EXPORT_SYMBOL(lirc_unregister_driver);
>>
>> int lirc_dev_fop_open(struct inode *inode, struct file *file)
>> {
>> - struct irctl *ir;
>> + struct irctl *ir = container_of(inode->i_cdev, struct irctl, cdev);
>> int retval;
>>
>> - if (iminor(inode) >= MAX_IRCTL_DEVICES) {
>> - pr_err("open result for %d is -ENODEV\n", iminor(inode));
>> - return -ENODEV;
>> - }
>> -
>> - if (mutex_lock_interruptible(&lirc_dev_lock))
>> - return -ERESTARTSYS;
>> + mutex_lock(&ir->mutex);
>>
>> - ir = irctls[iminor(inode)];
>> - mutex_unlock(&lirc_dev_lock);
>> -
>> - if (!ir) {
>> - retval = -ENODEV;
>> + if (ir->users) {
>> + retval = -EBUSY;
>> + mutex_unlock(&ir->mutex);
>> goto error;
>> }
>> + ir->users++;
>>
>> - dev_dbg(ir->d.dev, LOGHEAD "open called\n", ir->d.name, ir->d.minor);
>> -
>> - if (ir->d.minor == NOPLUG) {
>> - retval = -ENODEV;
>> - goto error;
>> - }
>> + mutex_unlock(&ir->mutex);
>>
>> - if (ir->open) {
>> - retval = -EBUSY;
>> - goto error;
>> - }
>> + dev_dbg(ir->d.dev, LOGHEAD "open called\n", ir->d.name, ir->d.minor);
>>
>> if (ir->d.rdev) {
>> retval = rc_open(ir->d.rdev);
>> @@ -329,8 +299,7 @@ int lirc_dev_fop_open(struct inode *inode, struct file *file)
>> if (ir->buf)
>> lirc_buffer_clear(ir->buf);
>>
>> - ir->open++;
>> -
>> + file->private_data = ir;
>> nonseekable_open(inode, file);
>>
>> return 0;
>> @@ -342,22 +311,14 @@ EXPORT_SYMBOL(lirc_dev_fop_open);
>>
>> int lirc_dev_fop_close(struct inode *inode, struct file *file)
>> {
>> - struct irctl *ir = irctls[iminor(inode)];
>> - int ret;
>> -
>> - if (!ir) {
>> - pr_err("called with invalid irctl\n");
>> - return -EINVAL;
>> - }
>> + struct irctl *ir = file->private_data;
>>
>> - ret = mutex_lock_killable(&lirc_dev_lock);
>> - WARN_ON(ret);
>> + mutex_lock(&ir->mutex);
>>
>> rc_close(ir->d.rdev);
>> + ir->users--;
>>
>> - ir->open--;
>> - if (!ret)
>> - mutex_unlock(&lirc_dev_lock);
>> + mutex_unlock(&ir->mutex);
>>
>> return 0;
>> }
>> @@ -365,26 +326,21 @@ EXPORT_SYMBOL(lirc_dev_fop_close);
>>
>> unsigned int lirc_dev_fop_poll(struct file *file, poll_table *wait)
>> {
>> - struct irctl *ir = irctls[iminor(file_inode(file))];
>> + struct irctl *ir = file->private_data;
>> unsigned int ret;
>>
>> - if (!ir) {
>> - pr_err("called with invalid irctl\n");
>> - return POLLERR;
>> - }
>> -
>> - if (!ir->attached)
>> + if (ir->dead)
>> return POLLHUP | POLLERR;
>>
>> - if (ir->buf) {
>> - poll_wait(file, &ir->buf->wait_poll, wait);
>> + if (!ir->buf)
>> + return POLLERR;
>> +
>> + poll_wait(file, &ir->buf->wait_poll, wait);
>>
>> - if (lirc_buffer_empty(ir->buf))
>> - ret = 0;
>> - else
>> - ret = POLLIN | POLLRDNORM;
>> - } else
>> - ret = POLLERR;
>> + if (lirc_buffer_empty(ir->buf))
>> + ret = 0;
>> + else
>> + ret = POLLIN | POLLRDNORM;
>>
>> dev_dbg(ir->d.dev, LOGHEAD "poll result = %d\n",
>> ir->d.name, ir->d.minor, ret);
>> @@ -395,25 +351,20 @@ EXPORT_SYMBOL(lirc_dev_fop_poll);
>>
>> long lirc_dev_fop_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>> {
>> + struct irctl *ir = file->private_data;
>> __u32 mode;
>> int result = 0;
>> - struct irctl *ir = irctls[iminor(file_inode(file))];
>> -
>> - if (!ir) {
>> - pr_err("no irctl found!\n");
>> - return -ENODEV;
>> - }
>>
>> dev_dbg(ir->d.dev, LOGHEAD "ioctl called (0x%x)\n",
>> ir->d.name, ir->d.minor, cmd);
>>
>> - if (ir->d.minor == NOPLUG || !ir->attached) {
>> + if (ir->dead) {
>> dev_err(ir->d.dev, LOGHEAD "ioctl result = -ENODEV\n",
>> ir->d.name, ir->d.minor);
>> return -ENODEV;
>> }
>>
>> - mutex_lock(&ir->irctl_lock);
>> + mutex_lock(&ir->mutex);
>>
>> switch (cmd) {
>> case LIRC_GET_FEATURES:
>> @@ -468,7 +419,7 @@ long lirc_dev_fop_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>> result = -ENOTTY;
>> }
>>
>> - mutex_unlock(&ir->irctl_lock);
>> + mutex_unlock(&ir->mutex);
>>
>> return result;
>> }
>> @@ -479,16 +430,11 @@ ssize_t lirc_dev_fop_read(struct file *file,
>> size_t length,
>> loff_t *ppos)
>> {
>> - struct irctl *ir = irctls[iminor(file_inode(file))];
>> + struct irctl *ir = file->private_data;
>> unsigned char *buf;
>> int ret = 0, written = 0;
>> DECLARE_WAITQUEUE(wait, current);
>>
>> - if (!ir) {
>> - pr_err("called with invalid irctl\n");
>> - return -ENODEV;
>> - }
>> -
>> if (!LIRC_CAN_REC(ir->d.features))
>> return -EINVAL;
>>
>> @@ -498,11 +444,12 @@ ssize_t lirc_dev_fop_read(struct file *file,
>> if (!buf)
>> return -ENOMEM;
>>
>> - if (mutex_lock_interruptible(&ir->irctl_lock)) {
>> + if (mutex_lock_interruptible(&ir->mutex)) {
>> ret = -ERESTARTSYS;
>> goto out_unlocked;
>> }
>> - if (!ir->attached) {
>> +
>> + if (ir->dead) {
>> ret = -ENODEV;
>> goto out_locked;
>> }
>> @@ -541,18 +488,18 @@ ssize_t lirc_dev_fop_read(struct file *file,
>> break;
>> }
>>
>> - mutex_unlock(&ir->irctl_lock);
>> + mutex_unlock(&ir->mutex);
>> set_current_state(TASK_INTERRUPTIBLE);
>> schedule();
>> set_current_state(TASK_RUNNING);
>>
>> - if (mutex_lock_interruptible(&ir->irctl_lock)) {
>> + if (mutex_lock_interruptible(&ir->mutex)) {
>> ret = -ERESTARTSYS;
>> remove_wait_queue(&ir->buf->wait_poll, &wait);
>> goto out_unlocked;
>> }
>>
>> - if (!ir->attached) {
>> + if (ir->dead) {
>> ret = -ENODEV;
>> goto out_locked;
>> }
>> @@ -570,7 +517,7 @@ ssize_t lirc_dev_fop_read(struct file *file,
>> remove_wait_queue(&ir->buf->wait_poll, &wait);
>>
>> out_locked:
>> - mutex_unlock(&ir->irctl_lock);
>> + mutex_unlock(&ir->mutex);
>>
>> out_unlocked:
>> kfree(buf);
>> @@ -581,7 +528,8 @@ EXPORT_SYMBOL(lirc_dev_fop_read);
>>
>> void *lirc_get_pdata(struct file *file)
>> {
>> - return irctls[iminor(file_inode(file))]->d.data;
>> + struct irctl *ir = file->private_data;
>> + return ir->d.data;
>> }
>> EXPORT_SYMBOL(lirc_get_pdata);
>>
>> @@ -596,7 +544,7 @@ static int __init lirc_dev_init(void)
>> return PTR_ERR(lirc_class);
>> }
>>
>> - retval = alloc_chrdev_region(&lirc_base_dev, 0, MAX_IRCTL_DEVICES,
>> + retval = alloc_chrdev_region(&lirc_base_dev, 0, LIRC_MAX_DEVICES,
>> IRCTL_DEV_NAME);
>> if (retval) {
>> class_destroy(lirc_class);
>> @@ -613,7 +561,7 @@ static int __init lirc_dev_init(void)
>> static void __exit lirc_dev_exit(void)
>> {
>> class_destroy(lirc_class);
>> - unregister_chrdev_region(lirc_base_dev, MAX_IRCTL_DEVICES);
>> + unregister_chrdev_region(lirc_base_dev, LIRC_MAX_DEVICES);
>> pr_info("module unloaded\n");
>> }
>>
>> diff --git a/drivers/staging/media/lirc/lirc_zilog.c b/drivers/staging/media/lirc/lirc_zilog.c
>> index 59e05aa1bc55..ffb70dee4547 100644
>> --- a/drivers/staging/media/lirc/lirc_zilog.c
>> +++ b/drivers/staging/media/lirc/lirc_zilog.c
>> @@ -183,11 +183,7 @@ static void release_ir_device(struct kref *ref)
>> * ir->open_count == 0 - happens on final close()
>> * ir_lock, tx_ref_lock, rx_ref_lock, all released
>> */
>> - if (ir->l.minor >= 0) {
>> - lirc_unregister_driver(ir->l.minor);
>> - ir->l.minor = -1;
>> - }
>> -
>> + lirc_unregister_driver(&ir->l);
>> if (kfifo_initialized(&ir->rbuf.fifo))
>> lirc_buffer_free(&ir->rbuf);
>> list_del(&ir->list);
>> @@ -1382,7 +1378,6 @@ static const struct file_operations lirc_fops = {
>>
>> static struct lirc_driver lirc_template = {
>> .name = "lirc_zilog",
>> - .minor = -1,
>> .code_length = 13,
>> .buffer_size = BUFLEN / 2,
>> .chunk_size = 2,
>> @@ -1597,14 +1592,13 @@ static int ir_probe(struct i2c_client *client, const struct i2c_device_id *id)
>> }
>>
>> /* register with lirc */
>> - ir->l.minor = lirc_register_driver(&ir->l);
>> - if (ir->l.minor < 0) {
>> + ret = lirc_register_driver(&ir->l);
>> + if (ret < 0) {
>> dev_err(tx->ir->l.dev,
>> - "%s: lirc_register_driver() failed: %i\n",
>> - __func__, ir->l.minor);
>> - ret = -EBADRQC;
>> + "%s: lirc_register_driver failed: %i\n", __func__, ret);
>> goto out_put_xx;
>> }
>> +
>> dev_info(ir->l.dev,
>> "IR unit on %s (i2c-%d) registered as lirc%d and ready\n",
>> adap->name, adap->nr, ir->l.minor);
>> diff --git a/include/media/lirc_dev.h b/include/media/lirc_dev.h
>> index 1f327e25a9be..f7629ff116a9 100644
>> --- a/include/media/lirc_dev.h
>> +++ b/include/media/lirc_dev.h
>> @@ -9,7 +9,6 @@
>> #ifndef _LINUX_LIRC_DEV_H
>> #define _LINUX_LIRC_DEV_H
>>
>> -#define MAX_IRCTL_DEVICES 8
>> #define BUFLEN 16
>>
>> #define mod(n, div) ((n) % (div))
>> @@ -164,6 +163,8 @@ static inline unsigned int lirc_buffer_write(struct lirc_buffer *buf,
>> * device.
>> *
>> * @owner: the module owning this struct
>> + *
>> + * @lirc_internal: lirc_dev bookkeeping data, don't touch.
>
>It's not a great name or comment :)
>
>Otherwise, it's a good idea.
>
>
>Sean
>
>> */
>> struct lirc_driver {
>> char name[40];
>> @@ -182,19 +183,12 @@ struct lirc_driver {
>> const struct file_operations *fops;
>> struct device *dev;
>> struct module *owner;
>> + void *lirc_internal;
>> };
>>
>> -/* following functions can be called ONLY from user context
>> - *
>> - * returns negative value on error or minor number
>> - * of the registered device if success
>> - * contents of the structure pointed by p is copied
>> - */
>> extern int lirc_register_driver(struct lirc_driver *d);
>>
>> -/* returns negative value on error or 0 if success
>> -*/
>> -extern int lirc_unregister_driver(int minor);
>> +extern void lirc_unregister_driver(struct lirc_driver *d);
>>
>> /* Returns the private data stored in the lirc_driver
>> * associated with the given device file pointer.
--
David Härdeman
