drivers/dax/super.c

   1 /*
   2  * Copyright(c) 2017 Intel Corporation. All rights reserved.
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of version 2 of the GNU General Public License as
   6  * published by the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful, but
   9  * WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * General Public License for more details.
  12  */
  13 #include <linux/pagemap.h>
  14 #include <linux/module.h>
  15 #include <linux/mount.h>
  16 #include <linux/magic.h>
  17 #include <linux/cdev.h>
  18 #include <linux/hash.h>
  19 #include <linux/slab.h>
  20 #include <linux/dax.h>
  21 #include <linux/fs.h>
  22
  23 static int nr_dax = CONFIG_NR_DEV_DAX;
  24 module_param(nr_dax, int, S_IRUGO);
  25 MODULE_PARM_DESC(nr_dax, "max number of dax device instances");
  26
  27 static dev_t dax_devt;
  28 DEFINE_STATIC_SRCU(dax_srcu);
  29 static struct vfsmount *dax_mnt;
  30 static DEFINE_IDA(dax_minor_ida);
  31 static struct kmem_cache *dax_cache __read_mostly;
  32 static struct super_block *dax_superblock __read_mostly;
  33
  34 #define DAX_HASH_SIZE (PAGE_SIZE / sizeof(struct hlist_head))
  35 static struct hlist_head dax_host_list[DAX_HASH_SIZE];
  36 static DEFINE_SPINLOCK(dax_host_lock);
  37
  38 int dax_read_lock(void)
  39 {
  40         return srcu_read_lock(&dax_srcu);
  41 }
  42 EXPORT_SYMBOL_GPL(dax_read_lock);
  43
  44 void dax_read_unlock(int id)
  45 {
  46         srcu_read_unlock(&dax_srcu, id);
  47 }
  48 EXPORT_SYMBOL_GPL(dax_read_unlock);
  49
  50 /**
  51  * struct dax_device - anchor object for dax services
  52  * @inode: core vfs
  53  * @cdev: optional character interface for "device dax"
  54  * @host: optional name for lookups where the device path is not available
  55  * @private: dax driver private data
  56  * @alive: !alive + rcu grace period == no new operations / mappings
  57  */
  58 struct dax_device {
  59         struct hlist_node list;
  60         struct inode inode;
  61         struct cdev cdev;
  62         const char *host;
  63         void *private;
  64         bool alive;
  65         const struct dax_operations *ops;
  66 };
  67
  68 /**
  69  * dax_direct_access() - translate a device pgoff to an absolute pfn
  70  * @dax_dev: a dax_device instance representing the logical memory range
  71  * @pgoff: offset in pages from the start of the device to translate
  72  * @nr_pages: number of consecutive pages caller can handle relative to @pfn
  73  * @kaddr: output parameter that returns a virtual address mapping of pfn
  74  * @pfn: output parameter that returns an absolute pfn translation of @pgoff
  75  *
  76  * Return: negative errno if an error occurs, otherwise the number of
  77  * pages accessible at the device relative @pgoff.
  78  */
  79 long dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, long nr_pages,
  80                 void **kaddr, pfn_t *pfn)
  81 {
  82         long avail;
  83
  84         /*
  85          * The device driver is allowed to sleep, in order to make the
  86          * memory directly accessible.
  87          */
  88         might_sleep();
  89
  90         if (!dax_dev)
  91                 return -EOPNOTSUPP;
  92
  93         if (!dax_alive(dax_dev))
  94                 return -ENXIO;
  95
  96         if (nr_pages < 0)
  97                 return nr_pages;
  98
  99         avail = dax_dev->ops->direct_access(dax_dev, pgoff, nr_pages,
 100                         kaddr, pfn);
 101         if (!avail)
 102                 return -ERANGE;
 103         return min(avail, nr_pages);
 104 }
 105 EXPORT_SYMBOL_GPL(dax_direct_access);
 106
 107 bool dax_alive(struct dax_device *dax_dev)
 108 {
 109         lockdep_assert_held(&dax_srcu);
 110         return dax_dev->alive;
 111 }
 112 EXPORT_SYMBOL_GPL(dax_alive);
 113
 114 static int dax_host_hash(const char *host)
 115 {
 116         return hashlen_hash(hashlen_string("DAX", host)) % DAX_HASH_SIZE;
 117 }
 118
 119 /*
 120  * Note, rcu is not protecting the liveness of dax_dev, rcu is ensuring
 121  * that any fault handlers or operations that might have seen
 122  * dax_alive(), have completed.  Any operations that start after
 123  * synchronize_srcu() has run will abort upon seeing !dax_alive().
 124  */
 125 void kill_dax(struct dax_device *dax_dev)
 126 {
 127         if (!dax_dev)
 128                 return;
 129
 130         dax_dev->alive = false;
 131
 132         synchronize_srcu(&dax_srcu);
 133
 134         spin_lock(&dax_host_lock);
 135         hlist_del_init(&dax_dev->list);
 136         spin_unlock(&dax_host_lock);
 137
 138         dax_dev->private = NULL;
 139 }
 140 EXPORT_SYMBOL_GPL(kill_dax);
 141
 142 static struct inode *dax_alloc_inode(struct super_block *sb)
 143 {
 144         struct dax_device *dax_dev;
 145
 146         dax_dev = kmem_cache_alloc(dax_cache, GFP_KERNEL);
 147         return &dax_dev->inode;
 148 }
 149
 150 static struct dax_device *to_dax_dev(struct inode *inode)
 151 {
 152         return container_of(inode, struct dax_device, inode);
 153 }
 154
 155 static void dax_i_callback(struct rcu_head *head)
 156 {
 157         struct inode *inode = container_of(head, struct inode, i_rcu);
 158         struct dax_device *dax_dev = to_dax_dev(inode);
 159
 160         kfree(dax_dev->host);
 161         dax_dev->host = NULL;
 162         ida_simple_remove(&dax_minor_ida, MINOR(inode->i_rdev));
 163         kmem_cache_free(dax_cache, dax_dev);
 164 }
 165
 166 static void dax_destroy_inode(struct inode *inode)
 167 {
 168         struct dax_device *dax_dev = to_dax_dev(inode);
 169
 170         WARN_ONCE(dax_dev->alive,
 171                         "kill_dax() must be called before final iput()\n");
 172         call_rcu(&inode->i_rcu, dax_i_callback);
 173 }
 174
 175 static const struct super_operations dax_sops = {
 176         .statfs = simple_statfs,
 177         .alloc_inode = dax_alloc_inode,
 178         .destroy_inode = dax_destroy_inode,
 179         .drop_inode = generic_delete_inode,
 180 };
 181
 182 static struct dentry *dax_mount(struct file_system_type *fs_type,
 183                 int flags, const char *dev_name, void *data)
 184 {
 185         return mount_pseudo(fs_type, "dax:", &dax_sops, NULL, DAXFS_MAGIC);
 186 }
 187
 188 static struct file_system_type dax_fs_type = {
 189         .name = "dax",
 190         .mount = dax_mount,
 191         .kill_sb = kill_anon_super,
 192 };
 193
 194 static int dax_test(struct inode *inode, void *data)
 195 {
 196         dev_t devt = *(dev_t *) data;
 197
 198         return inode->i_rdev == devt;
 199 }
 200
 201 static int dax_set(struct inode *inode, void *data)
 202 {
 203         dev_t devt = *(dev_t *) data;
 204
 205         inode->i_rdev = devt;
 206         return 0;
 207 }
 208
 209 static struct dax_device *dax_dev_get(dev_t devt)
 210 {
 211         struct dax_device *dax_dev;
 212         struct inode *inode;
 213
 214         inode = iget5_locked(dax_superblock, hash_32(devt + DAXFS_MAGIC, 31),
 215                         dax_test, dax_set, &devt);
 216
 217         if (!inode)
 218                 return NULL;
 219
 220         dax_dev = to_dax_dev(inode);
 221         if (inode->i_state & I_NEW) {
 222                 dax_dev->alive = true;
 223                 inode->i_cdev = &dax_dev->cdev;
 224                 inode->i_mode = S_IFCHR;
 225                 inode->i_flags = S_DAX;
 226                 mapping_set_gfp_mask(&inode->i_data, GFP_USER);
 227                 unlock_new_inode(inode);
 228         }
 229
 230         return dax_dev;
 231 }
 232
 233 static void dax_add_host(struct dax_device *dax_dev, const char *host)
 234 {
 235         int hash;
 236
 237         /*
 238          * Unconditionally init dax_dev since it's coming from a
 239          * non-zeroed slab cache
 240          */
 241         INIT_HLIST_NODE(&dax_dev->list);
 242         dax_dev->host = host;
 243         if (!host)
 244                 return;
 245
 246         hash = dax_host_hash(host);
 247         spin_lock(&dax_host_lock);
 248         hlist_add_head(&dax_dev->list, &dax_host_list[hash]);
 249         spin_unlock(&dax_host_lock);
 250 }
 251
 252 struct dax_device *alloc_dax(void *private, const char *__host,
 253                 const struct dax_operations *ops)
 254 {
 255         struct dax_device *dax_dev;
 256         const char *host;
 257         dev_t devt;
 258         int minor;
 259
 260         host = kstrdup(__host, GFP_KERNEL);
 261         if (__host && !host)
 262                 return NULL;
 263
 264         minor = ida_simple_get(&dax_minor_ida, 0, nr_dax, GFP_KERNEL);
 265         if (minor < 0)
 266                 goto err_minor;
 267
 268         devt = MKDEV(MAJOR(dax_devt), minor);
 269         dax_dev = dax_dev_get(devt);
 270         if (!dax_dev)
 271                 goto err_dev;
 272
 273         dax_add_host(dax_dev, host);
 274         dax_dev->ops = ops;
 275         dax_dev->private = private;
 276         return dax_dev;
 277
 278  err_dev:
 279         ida_simple_remove(&dax_minor_ida, minor);
 280  err_minor:
 281         kfree(host);
 282         return NULL;
 283 }
 284 EXPORT_SYMBOL_GPL(alloc_dax);
 285
 286 void put_dax(struct dax_device *dax_dev)
 287 {
 288         if (!dax_dev)
 289                 return;
 290         iput(&dax_dev->inode);
 291 }
 292 EXPORT_SYMBOL_GPL(put_dax);
 293
 294 /**
 295  * dax_get_by_host() - temporary lookup mechanism for filesystem-dax
 296  * @host: alternate name for the device registered by a dax driver
 297  */
 298 struct dax_device *dax_get_by_host(const char *host)
 299 {
 300         struct dax_device *dax_dev, *found = NULL;
 301         int hash, id;
 302
 303         if (!host)
 304                 return NULL;
 305
 306         hash = dax_host_hash(host);
 307
 308         id = dax_read_lock();
 309         spin_lock(&dax_host_lock);
 310         hlist_for_each_entry(dax_dev, &dax_host_list[hash], list) {
 311                 if (!dax_alive(dax_dev)
 312                                 || strcmp(host, dax_dev->host) != 0)
 313                         continue;
 314
 315                 if (igrab(&dax_dev->inode))
 316                         found = dax_dev;
 317                 break;
 318         }
 319         spin_unlock(&dax_host_lock);
 320         dax_read_unlock(id);
 321
 322         return found;
 323 }
 324 EXPORT_SYMBOL_GPL(dax_get_by_host);
 325
 326 /**
 327  * inode_dax: convert a public inode into its dax_dev
 328  * @inode: An inode with i_cdev pointing to a dax_dev
 329  *
 330  * Note this is not equivalent to to_dax_dev() which is for private
 331  * internal use where we know the inode filesystem type == dax_fs_type.
 332  */
 333 struct dax_device *inode_dax(struct inode *inode)
 334 {
 335         struct cdev *cdev = inode->i_cdev;
 336
 337         return container_of(cdev, struct dax_device, cdev);
 338 }
 339 EXPORT_SYMBOL_GPL(inode_dax);
 340
 341 struct inode *dax_inode(struct dax_device *dax_dev)
 342 {
 343         return &dax_dev->inode;
 344 }
 345 EXPORT_SYMBOL_GPL(dax_inode);
 346
 347 void *dax_get_private(struct dax_device *dax_dev)
 348 {
 349         return dax_dev->private;
 350 }
 351 EXPORT_SYMBOL_GPL(dax_get_private);
 352
 353 static void init_once(void *_dax_dev)
 354 {
 355         struct dax_device *dax_dev = _dax_dev;
 356         struct inode *inode = &dax_dev->inode;
 357
 358         inode_init_once(inode);
 359 }
 360
 361 static int __dax_fs_init(void)
 362 {
 363         int rc;
 364
 365         dax_cache = kmem_cache_create("dax_cache", sizeof(struct dax_device), 0,
 366                         (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT|
 367                          SLAB_MEM_SPREAD|SLAB_ACCOUNT),
 368                         init_once);
 369         if (!dax_cache)
 370                 return -ENOMEM;
 371
 372         rc = register_filesystem(&dax_fs_type);
 373         if (rc)
 374                 goto err_register_fs;
 375
 376         dax_mnt = kern_mount(&dax_fs_type);
 377         if (IS_ERR(dax_mnt)) {
 378                 rc = PTR_ERR(dax_mnt);
 379                 goto err_mount;
 380         }
 381         dax_superblock = dax_mnt->mnt_sb;
 382
 383         return 0;
 384
 385  err_mount:
 386         unregister_filesystem(&dax_fs_type);
 387  err_register_fs:
 388         kmem_cache_destroy(dax_cache);
 389
 390         return rc;
 391 }
 392
 393 static void __dax_fs_exit(void)
 394 {
 395         kern_unmount(dax_mnt);
 396         unregister_filesystem(&dax_fs_type);
 397         kmem_cache_destroy(dax_cache);
 398 }
 399
 400 static int __init dax_fs_init(void)
 401 {
 402         int rc;
 403
 404         rc = __dax_fs_init();
 405         if (rc)
 406                 return rc;
 407
 408         nr_dax = max(nr_dax, 256);
 409         rc = alloc_chrdev_region(&dax_devt, 0, nr_dax, "dax");
 410         if (rc)
 411                 __dax_fs_exit();
 412         return rc;
 413 }
 414
 415 static void __exit dax_fs_exit(void)
 416 {
 417         unregister_chrdev_region(dax_devt, nr_dax);
 418         ida_destroy(&dax_minor_ida);
 419         __dax_fs_exit();
 420 }
 421
 422 MODULE_AUTHOR("Intel Corporation");
 423 MODULE_LICENSE("GPL v2");
 424 subsys_initcall(dax_fs_init);
 425 module_exit(dax_fs_exit);