drivers/char/raw.c

   1 /*
   2  * linux/drivers/char/raw.c
   3  *
   4  * Front-end raw character devices.  These can be bound to any block
   5  * devices to provide genuine Unix raw character device semantics.
   6  *
   7  * We reserve minor number 0 for a control interface.  ioctl()s on this
   8  * device are used to bind the other minor numbers to block devices.
   9  */
  10
  11 #include <linux/init.h>
  12 #include <linux/fs.h>
  13 #include <linux/major.h>
  14 #include <linux/blkdev.h>
  15 #include <linux/module.h>
  16 #include <linux/raw.h>
  17 #include <linux/capability.h>
  18 #include <linux/uio.h>
  19 #include <linux/cdev.h>
  20 #include <linux/device.h>
  21 #include <linux/mutex.h>
  22 #include <linux/smp_lock.h>
  23 #include <linux/gfp.h>
  24
  25 #include <asm/uaccess.h>
  26
  27 struct raw_device_data {
  28         struct block_device *binding;
  29         int inuse;
  30 };
  31
  32 static struct class *raw_class;
  33 static struct raw_device_data raw_devices[MAX_RAW_MINORS];
  34 static DEFINE_MUTEX(raw_mutex);
  35 static const struct file_operations raw_ctl_fops; /* forward declaration */
  36
  37 /*
  38  * Open/close code for raw IO.
  39  *
  40  * We just rewrite the i_mapping for the /dev/raw/rawN file descriptor to
  41  * point at the blockdev's address_space and set the file handle to use
  42  * O_DIRECT.
  43  *
  44  * Set the device's soft blocksize to the minimum possible.  This gives the
  45  * finest possible alignment and has no adverse impact on performance.
  46  */
  47 static int raw_open(struct inode *inode, struct file *filp)
  48 {
  49         const int minor = iminor(inode);
  50         struct block_device *bdev;
  51         int err;
  52
  53         if (minor == 0) {       /* It is the control device */
  54                 filp->f_op = &raw_ctl_fops;
  55                 return 0;
  56         }
  57
  58         lock_kernel();
  59         mutex_lock(&raw_mutex);
  60
  61         /*
  62          * All we need to do on open is check that the device is bound.
  63          */
  64         bdev = raw_devices[minor].binding;
  65         err = -ENODEV;
  66         if (!bdev)
  67                 goto out;
  68         igrab(bdev->bd_inode);
  69         err = blkdev_get(bdev, filp->f_mode);
  70         if (err)
  71                 goto out;
  72         err = bd_claim(bdev, raw_open);
  73         if (err)
  74                 goto out1;
  75         err = set_blocksize(bdev, bdev_logical_block_size(bdev));
  76         if (err)
  77                 goto out2;
  78         filp->f_flags |= O_DIRECT;
  79         filp->f_mapping = bdev->bd_inode->i_mapping;
  80         if (++raw_devices[minor].inuse == 1)
  81                 filp->f_path.dentry->d_inode->i_mapping =
  82                         bdev->bd_inode->i_mapping;
  83         filp->private_data = bdev;
  84         mutex_unlock(&raw_mutex);
  85         unlock_kernel();
  86         return 0;
  87
  88 out2:
  89         bd_release(bdev);
  90 out1:
  91         blkdev_put(bdev, filp->f_mode);
  92 out:
  93         mutex_unlock(&raw_mutex);
  94         unlock_kernel();
  95         return err;
  96 }
  97
  98 /*
  99  * When the final fd which refers to this character-special node is closed, we
 100  * make its ->mapping point back at its own i_data.
 101  */
 102 static int raw_release(struct inode *inode, struct file *filp)
 103 {
 104         const int minor= iminor(inode);
 105         struct block_device *bdev;
 106
 107         mutex_lock(&raw_mutex);
 108         bdev = raw_devices[minor].binding;
 109         if (--raw_devices[minor].inuse == 0) {
 110                 /* Here  inode->i_mapping == bdev->bd_inode->i_mapping  */
 111                 inode->i_mapping = &inode->i_data;
 112                 inode->i_mapping->backing_dev_info = &default_backing_dev_info;
 113         }
 114         mutex_unlock(&raw_mutex);
 115
 116         bd_release(bdev);
 117         blkdev_put(bdev, filp->f_mode);
 118         return 0;
 119 }
 120
 121 /*
 122  * Forward ioctls to the underlying block device.
 123  */
 124 static int
 125 raw_ioctl(struct inode *inode, struct file *filp,
 126                   unsigned int command, unsigned long arg)
 127 {
 128         struct block_device *bdev = filp->private_data;
 129
 130         return blkdev_ioctl(bdev, 0, command, arg);
 131 }
 132
 133 static void bind_device(struct raw_config_request *rq)
 134 {
 135         device_destroy(raw_class, MKDEV(RAW_MAJOR, rq->raw_minor));
 136         device_create(raw_class, NULL, MKDEV(RAW_MAJOR, rq->raw_minor), NULL,
 137                       "raw%d", rq->raw_minor);
 138 }
 139
 140 /*
 141  * Deal with ioctls against the raw-device control interface, to bind
 142  * and unbind other raw devices.
 143  */
 144 static int raw_ctl_ioctl(struct inode *inode, struct file *filp,
 145                         unsigned int command, unsigned long arg)
 146 {
 147         struct raw_config_request rq;
 148         struct raw_device_data *rawdev;
 149         int err = 0;
 150
 151         switch (command) {
 152         case RAW_SETBIND:
 153         case RAW_GETBIND:
 154
 155                 /* First, find out which raw minor we want */
 156
 157                 if (copy_from_user(&rq, (void __user *) arg, sizeof(rq))) {
 158                         err = -EFAULT;
 159                         goto out;
 160                 }
 161
 162                 if (rq.raw_minor <= 0 || rq.raw_minor >= MAX_RAW_MINORS) {
 163                         err = -EINVAL;
 164                         goto out;
 165                 }
 166                 rawdev = &raw_devices[rq.raw_minor];
 167
 168                 if (command == RAW_SETBIND) {
 169                         dev_t dev;
 170
 171                         /*
 172                          * This is like making block devices, so demand the
 173                          * same capability
 174                          */
 175                         if (!capable(CAP_SYS_ADMIN)) {
 176                                 err = -EPERM;
 177                                 goto out;
 178                         }
 179
 180                         /*
 181                          * For now, we don't need to check that the underlying
 182                          * block device is present or not: we can do that when
 183                          * the raw device is opened.  Just check that the
 184                          * major/minor numbers make sense.
 185                          */
 186
 187                         dev = MKDEV(rq.block_major, rq.block_minor);
 188                         if ((rq.block_major == 0 && rq.block_minor != 0) ||
 189                                         MAJOR(dev) != rq.block_major ||
 190                                         MINOR(dev) != rq.block_minor) {
 191                                 err = -EINVAL;
 192                                 goto out;
 193                         }
 194
 195                         mutex_lock(&raw_mutex);
 196                         if (rawdev->inuse) {
 197                                 mutex_unlock(&raw_mutex);
 198                                 err = -EBUSY;
 199                                 goto out;
 200                         }
 201                         if (rawdev->binding) {
 202                                 bdput(rawdev->binding);
 203                                 module_put(THIS_MODULE);
 204                         }
 205                         if (rq.block_major == 0 && rq.block_minor == 0) {
 206                                 /* unbind */
 207                                 rawdev->binding = NULL;
 208                                 device_destroy(raw_class,
 209                                                 MKDEV(RAW_MAJOR, rq.raw_minor));
 210                         } else {
 211                                 rawdev->binding = bdget(dev);
 212                                 if (rawdev->binding == NULL)
 213                                         err = -ENOMEM;
 214                                 else {
 215                                         __module_get(THIS_MODULE);
 216                                         bind_device(&rq);
 217                                 }
 218                         }
 219                         mutex_unlock(&raw_mutex);
 220                 } else {
 221                         struct block_device *bdev;
 222
 223                         mutex_lock(&raw_mutex);
 224                         bdev = rawdev->binding;
 225                         if (bdev) {
 226                                 rq.block_major = MAJOR(bdev->bd_dev);
 227                                 rq.block_minor = MINOR(bdev->bd_dev);
 228                         } else {
 229                                 rq.block_major = rq.block_minor = 0;
 230                         }
 231                         mutex_unlock(&raw_mutex);
 232                         if (copy_to_user((void __user *)arg, &rq, sizeof(rq))) {
 233                                 err = -EFAULT;
 234                                 goto out;
 235                         }
 236                 }
 237                 break;
 238         default:
 239                 err = -EINVAL;
 240                 break;
 241         }
 242 out:
 243         return err;
 244 }
 245
 246 static const struct file_operations raw_fops = {
 247         .read   =       do_sync_read,
 248         .aio_read =     generic_file_aio_read,
 249         .write  =       do_sync_write,
 250         .aio_write =    blkdev_aio_write,
 251         .open   =       raw_open,
 252         .release=       raw_release,
 253         .ioctl  =       raw_ioctl,
 254         .owner  =       THIS_MODULE,
 255 };
 256
 257 static const struct file_operations raw_ctl_fops = {
 258         .ioctl  =       raw_ctl_ioctl,
 259         .open   =       raw_open,
 260         .owner  =       THIS_MODULE,
 261 };
 262
 263 static struct cdev raw_cdev;
 264
 265 static char *raw_devnode(struct device *dev, mode_t *mode)
 266 {
 267         return kasprintf(GFP_KERNEL, "raw/%s", dev_name(dev));
 268 }
 269
 270 static int __init raw_init(void)
 271 {
 272         dev_t dev = MKDEV(RAW_MAJOR, 0);
 273         int ret;
 274
 275         ret = register_chrdev_region(dev, MAX_RAW_MINORS, "raw");
 276         if (ret)
 277                 goto error;
 278
 279         cdev_init(&raw_cdev, &raw_fops);
 280         ret = cdev_add(&raw_cdev, dev, MAX_RAW_MINORS);
 281         if (ret) {
 282                 kobject_put(&raw_cdev.kobj);
 283                 goto error_region;
 284         }
 285
 286         raw_class = class_create(THIS_MODULE, "raw");
 287         if (IS_ERR(raw_class)) {
 288                 printk(KERN_ERR "Error creating raw class.\n");
 289                 cdev_del(&raw_cdev);
 290                 ret = PTR_ERR(raw_class);
 291                 goto error_region;
 292         }
 293         raw_class->devnode = raw_devnode;
 294         device_create(raw_class, NULL, MKDEV(RAW_MAJOR, 0), NULL, "rawctl");
 295
 296         return 0;
 297
 298 error_region:
 299         unregister_chrdev_region(dev, MAX_RAW_MINORS);
 300 error:
 301         return ret;
 302 }
 303
 304 static void __exit raw_exit(void)
 305 {
 306         device_destroy(raw_class, MKDEV(RAW_MAJOR, 0));
 307         class_destroy(raw_class);
 308         cdev_del(&raw_cdev);
 309         unregister_chrdev_region(MKDEV(RAW_MAJOR, 0), MAX_RAW_MINORS);
 310 }
 311
 312 module_init(raw_init);
 313 module_exit(raw_exit);
 314 MODULE_LICENSE("GPL");