linux/fs/configfs/file.c
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   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * file.c - operations for regular (text) files.
   4 *
   5 * Based on sysfs:
   6 *      sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
   7 *
   8 * configfs Copyright (C) 2005 Oracle.  All rights reserved.
   9 */
  10
  11#include <linux/fs.h>
  12#include <linux/module.h>
  13#include <linux/slab.h>
  14#include <linux/mutex.h>
  15#include <linux/vmalloc.h>
  16#include <linux/uaccess.h>
  17
  18#include <linux/configfs.h>
  19#include "configfs_internal.h"
  20
  21/*
  22 * A simple attribute can only be 4096 characters.  Why 4k?  Because the
  23 * original code limited it to PAGE_SIZE.  That's a bad idea, though,
  24 * because an attribute of 16k on ia64 won't work on x86.  So we limit to
  25 * 4k, our minimum common page size.
  26 */
  27#define SIMPLE_ATTR_SIZE 4096
  28
  29struct configfs_buffer {
  30        size_t                  count;
  31        loff_t                  pos;
  32        char                    * page;
  33        struct configfs_item_operations * ops;
  34        struct mutex            mutex;
  35        int                     needs_read_fill;
  36        bool                    read_in_progress;
  37        bool                    write_in_progress;
  38        char                    *bin_buffer;
  39        int                     bin_buffer_size;
  40        int                     cb_max_size;
  41        struct config_item      *item;
  42        struct module           *owner;
  43        union {
  44                struct configfs_attribute       *attr;
  45                struct configfs_bin_attribute   *bin_attr;
  46        };
  47};
  48
  49static inline struct configfs_fragment *to_frag(struct file *file)
  50{
  51        struct configfs_dirent *sd = file->f_path.dentry->d_fsdata;
  52
  53        return sd->s_frag;
  54}
  55
  56static int fill_read_buffer(struct file *file, struct configfs_buffer *buffer)
  57{
  58        struct configfs_fragment *frag = to_frag(file);
  59        ssize_t count = -ENOENT;
  60
  61        if (!buffer->page)
  62                buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
  63        if (!buffer->page)
  64                return -ENOMEM;
  65
  66        down_read(&frag->frag_sem);
  67        if (!frag->frag_dead)
  68                count = buffer->attr->show(buffer->item, buffer->page);
  69        up_read(&frag->frag_sem);
  70
  71        if (count < 0)
  72                return count;
  73        if (WARN_ON_ONCE(count > (ssize_t)SIMPLE_ATTR_SIZE))
  74                return -EIO;
  75        buffer->needs_read_fill = 0;
  76        buffer->count = count;
  77        return 0;
  78}
  79
  80/**
  81 *      configfs_read_file - read an attribute.
  82 *      @file:  file pointer.
  83 *      @buf:   buffer to fill.
  84 *      @count: number of bytes to read.
  85 *      @ppos:  starting offset in file.
  86 *
  87 *      Userspace wants to read an attribute file. The attribute descriptor
  88 *      is in the file's ->d_fsdata. The target item is in the directory's
  89 *      ->d_fsdata.
  90 *
  91 *      We call fill_read_buffer() to allocate and fill the buffer from the
  92 *      item's show() method exactly once (if the read is happening from
  93 *      the beginning of the file). That should fill the entire buffer with
  94 *      all the data the item has to offer for that attribute.
  95 *      We then call flush_read_buffer() to copy the buffer to userspace
  96 *      in the increments specified.
  97 */
  98
  99static ssize_t
 100configfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 101{
 102        struct configfs_buffer *buffer = file->private_data;
 103        ssize_t retval = 0;
 104
 105        mutex_lock(&buffer->mutex);
 106        if (buffer->needs_read_fill) {
 107                retval = fill_read_buffer(file, buffer);
 108                if (retval)
 109                        goto out;
 110        }
 111        pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",
 112                 __func__, count, *ppos, buffer->page);
 113        retval = simple_read_from_buffer(buf, count, ppos, buffer->page,
 114                                         buffer->count);
 115out:
 116        mutex_unlock(&buffer->mutex);
 117        return retval;
 118}
 119
 120/**
 121 *      configfs_read_bin_file - read a binary attribute.
 122 *      @file:  file pointer.
 123 *      @buf:   buffer to fill.
 124 *      @count: number of bytes to read.
 125 *      @ppos:  starting offset in file.
 126 *
 127 *      Userspace wants to read a binary attribute file. The attribute
 128 *      descriptor is in the file's ->d_fsdata. The target item is in the
 129 *      directory's ->d_fsdata.
 130 *
 131 *      We check whether we need to refill the buffer. If so we will
 132 *      call the attributes' attr->read() twice. The first time we
 133 *      will pass a NULL as a buffer pointer, which the attributes' method
 134 *      will use to return the size of the buffer required. If no error
 135 *      occurs we will allocate the buffer using vmalloc and call
 136 *      attr->read() again passing that buffer as an argument.
 137 *      Then we just copy to user-space using simple_read_from_buffer.
 138 */
 139
 140static ssize_t
 141configfs_read_bin_file(struct file *file, char __user *buf,
 142                       size_t count, loff_t *ppos)
 143{
 144        struct configfs_fragment *frag = to_frag(file);
 145        struct configfs_buffer *buffer = file->private_data;
 146        ssize_t retval = 0;
 147        ssize_t len = min_t(size_t, count, PAGE_SIZE);
 148
 149        mutex_lock(&buffer->mutex);
 150
 151        /* we don't support switching read/write modes */
 152        if (buffer->write_in_progress) {
 153                retval = -ETXTBSY;
 154                goto out;
 155        }
 156        buffer->read_in_progress = true;
 157
 158        if (buffer->needs_read_fill) {
 159                /* perform first read with buf == NULL to get extent */
 160                down_read(&frag->frag_sem);
 161                if (!frag->frag_dead)
 162                        len = buffer->bin_attr->read(buffer->item, NULL, 0);
 163                else
 164                        len = -ENOENT;
 165                up_read(&frag->frag_sem);
 166                if (len <= 0) {
 167                        retval = len;
 168                        goto out;
 169                }
 170
 171                /* do not exceed the maximum value */
 172                if (buffer->cb_max_size && len > buffer->cb_max_size) {
 173                        retval = -EFBIG;
 174                        goto out;
 175                }
 176
 177                buffer->bin_buffer = vmalloc(len);
 178                if (buffer->bin_buffer == NULL) {
 179                        retval = -ENOMEM;
 180                        goto out;
 181                }
 182                buffer->bin_buffer_size = len;
 183
 184                /* perform second read to fill buffer */
 185                down_read(&frag->frag_sem);
 186                if (!frag->frag_dead)
 187                        len = buffer->bin_attr->read(buffer->item,
 188                                                     buffer->bin_buffer, len);
 189                else
 190                        len = -ENOENT;
 191                up_read(&frag->frag_sem);
 192                if (len < 0) {
 193                        retval = len;
 194                        vfree(buffer->bin_buffer);
 195                        buffer->bin_buffer_size = 0;
 196                        buffer->bin_buffer = NULL;
 197                        goto out;
 198                }
 199
 200                buffer->needs_read_fill = 0;
 201        }
 202
 203        retval = simple_read_from_buffer(buf, count, ppos, buffer->bin_buffer,
 204                                        buffer->bin_buffer_size);
 205out:
 206        mutex_unlock(&buffer->mutex);
 207        return retval;
 208}
 209
 210
 211/**
 212 *      fill_write_buffer - copy buffer from userspace.
 213 *      @buffer:        data buffer for file.
 214 *      @buf:           data from user.
 215 *      @count:         number of bytes in @userbuf.
 216 *
 217 *      Allocate @buffer->page if it hasn't been already, then
 218 *      copy the user-supplied buffer into it.
 219 */
 220
 221static int
 222fill_write_buffer(struct configfs_buffer * buffer, const char __user * buf, size_t count)
 223{
 224        int error;
 225
 226        if (!buffer->page)
 227                buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
 228        if (!buffer->page)
 229                return -ENOMEM;
 230
 231        if (count >= SIMPLE_ATTR_SIZE)
 232                count = SIMPLE_ATTR_SIZE - 1;
 233        error = copy_from_user(buffer->page,buf,count);
 234        buffer->needs_read_fill = 1;
 235        /* if buf is assumed to contain a string, terminate it by \0,
 236         * so e.g. sscanf() can scan the string easily */
 237        buffer->page[count] = 0;
 238        return error ? -EFAULT : count;
 239}
 240
 241static int
 242flush_write_buffer(struct file *file, struct configfs_buffer *buffer, size_t count)
 243{
 244        struct configfs_fragment *frag = to_frag(file);
 245        int res = -ENOENT;
 246
 247        down_read(&frag->frag_sem);
 248        if (!frag->frag_dead)
 249                res = buffer->attr->store(buffer->item, buffer->page, count);
 250        up_read(&frag->frag_sem);
 251        return res;
 252}
 253
 254
 255/**
 256 *      configfs_write_file - write an attribute.
 257 *      @file:  file pointer
 258 *      @buf:   data to write
 259 *      @count: number of bytes
 260 *      @ppos:  starting offset
 261 *
 262 *      Similar to configfs_read_file(), though working in the opposite direction.
 263 *      We allocate and fill the data from the user in fill_write_buffer(),
 264 *      then push it to the config_item in flush_write_buffer().
 265 *      There is no easy way for us to know if userspace is only doing a partial
 266 *      write, so we don't support them. We expect the entire buffer to come
 267 *      on the first write.
 268 *      Hint: if you're writing a value, first read the file, modify only
 269 *      the value you're changing, then write entire buffer back.
 270 */
 271
 272static ssize_t
 273configfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 274{
 275        struct configfs_buffer *buffer = file->private_data;
 276        ssize_t len;
 277
 278        mutex_lock(&buffer->mutex);
 279        len = fill_write_buffer(buffer, buf, count);
 280        if (len > 0)
 281                len = flush_write_buffer(file, buffer, len);
 282        if (len > 0)
 283                *ppos += len;
 284        mutex_unlock(&buffer->mutex);
 285        return len;
 286}
 287
 288/**
 289 *      configfs_write_bin_file - write a binary attribute.
 290 *      @file:  file pointer
 291 *      @buf:   data to write
 292 *      @count: number of bytes
 293 *      @ppos:  starting offset
 294 *
 295 *      Writing to a binary attribute file is similar to a normal read.
 296 *      We buffer the consecutive writes (binary attribute files do not
 297 *      support lseek) in a continuously growing buffer, but we don't
 298 *      commit until the close of the file.
 299 */
 300
 301static ssize_t
 302configfs_write_bin_file(struct file *file, const char __user *buf,
 303                        size_t count, loff_t *ppos)
 304{
 305        struct configfs_buffer *buffer = file->private_data;
 306        void *tbuf = NULL;
 307        ssize_t len;
 308
 309        mutex_lock(&buffer->mutex);
 310
 311        /* we don't support switching read/write modes */
 312        if (buffer->read_in_progress) {
 313                len = -ETXTBSY;
 314                goto out;
 315        }
 316        buffer->write_in_progress = true;
 317
 318        /* buffer grows? */
 319        if (*ppos + count > buffer->bin_buffer_size) {
 320
 321                if (buffer->cb_max_size &&
 322                        *ppos + count > buffer->cb_max_size) {
 323                        len = -EFBIG;
 324                        goto out;
 325                }
 326
 327                tbuf = vmalloc(*ppos + count);
 328                if (tbuf == NULL) {
 329                        len = -ENOMEM;
 330                        goto out;
 331                }
 332
 333                /* copy old contents */
 334                if (buffer->bin_buffer) {
 335                        memcpy(tbuf, buffer->bin_buffer,
 336                                buffer->bin_buffer_size);
 337                        vfree(buffer->bin_buffer);
 338                }
 339
 340                /* clear the new area */
 341                memset(tbuf + buffer->bin_buffer_size, 0,
 342                        *ppos + count - buffer->bin_buffer_size);
 343                buffer->bin_buffer = tbuf;
 344                buffer->bin_buffer_size = *ppos + count;
 345        }
 346
 347        len = simple_write_to_buffer(buffer->bin_buffer,
 348                        buffer->bin_buffer_size, ppos, buf, count);
 349out:
 350        mutex_unlock(&buffer->mutex);
 351        return len;
 352}
 353
 354static int __configfs_open_file(struct inode *inode, struct file *file, int type)
 355{
 356        struct dentry *dentry = file->f_path.dentry;
 357        struct configfs_fragment *frag = to_frag(file);
 358        struct configfs_attribute *attr;
 359        struct configfs_buffer *buffer;
 360        int error;
 361
 362        error = -ENOMEM;
 363        buffer = kzalloc(sizeof(struct configfs_buffer), GFP_KERNEL);
 364        if (!buffer)
 365                goto out;
 366
 367        error = -ENOENT;
 368        down_read(&frag->frag_sem);
 369        if (unlikely(frag->frag_dead))
 370                goto out_free_buffer;
 371
 372        error = -EINVAL;
 373        buffer->item = to_item(dentry->d_parent);
 374        if (!buffer->item)
 375                goto out_free_buffer;
 376
 377        attr = to_attr(dentry);
 378        if (!attr)
 379                goto out_free_buffer;
 380
 381        if (type & CONFIGFS_ITEM_BIN_ATTR) {
 382                buffer->bin_attr = to_bin_attr(dentry);
 383                buffer->cb_max_size = buffer->bin_attr->cb_max_size;
 384        } else {
 385                buffer->attr = attr;
 386        }
 387
 388        buffer->owner = attr->ca_owner;
 389        /* Grab the module reference for this attribute if we have one */
 390        error = -ENODEV;
 391        if (!try_module_get(buffer->owner))
 392                goto out_free_buffer;
 393
 394        error = -EACCES;
 395        if (!buffer->item->ci_type)
 396                goto out_put_module;
 397
 398        buffer->ops = buffer->item->ci_type->ct_item_ops;
 399
 400        /* File needs write support.
 401         * The inode's perms must say it's ok,
 402         * and we must have a store method.
 403         */
 404        if (file->f_mode & FMODE_WRITE) {
 405                if (!(inode->i_mode & S_IWUGO))
 406                        goto out_put_module;
 407                if ((type & CONFIGFS_ITEM_ATTR) && !attr->store)
 408                        goto out_put_module;
 409                if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->write)
 410                        goto out_put_module;
 411        }
 412
 413        /* File needs read support.
 414         * The inode's perms must say it's ok, and we there
 415         * must be a show method for it.
 416         */
 417        if (file->f_mode & FMODE_READ) {
 418                if (!(inode->i_mode & S_IRUGO))
 419                        goto out_put_module;
 420                if ((type & CONFIGFS_ITEM_ATTR) && !attr->show)
 421                        goto out_put_module;
 422                if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->read)
 423                        goto out_put_module;
 424        }
 425
 426        mutex_init(&buffer->mutex);
 427        buffer->needs_read_fill = 1;
 428        buffer->read_in_progress = false;
 429        buffer->write_in_progress = false;
 430        file->private_data = buffer;
 431        up_read(&frag->frag_sem);
 432        return 0;
 433
 434out_put_module:
 435        module_put(buffer->owner);
 436out_free_buffer:
 437        up_read(&frag->frag_sem);
 438        kfree(buffer);
 439out:
 440        return error;
 441}
 442
 443static int configfs_release(struct inode *inode, struct file *filp)
 444{
 445        struct configfs_buffer *buffer = filp->private_data;
 446
 447        module_put(buffer->owner);
 448        if (buffer->page)
 449                free_page((unsigned long)buffer->page);
 450        mutex_destroy(&buffer->mutex);
 451        kfree(buffer);
 452        return 0;
 453}
 454
 455static int configfs_open_file(struct inode *inode, struct file *filp)
 456{
 457        return __configfs_open_file(inode, filp, CONFIGFS_ITEM_ATTR);
 458}
 459
 460static int configfs_open_bin_file(struct inode *inode, struct file *filp)
 461{
 462        return __configfs_open_file(inode, filp, CONFIGFS_ITEM_BIN_ATTR);
 463}
 464
 465static int configfs_release_bin_file(struct inode *inode, struct file *file)
 466{
 467        struct configfs_buffer *buffer = file->private_data;
 468
 469        buffer->read_in_progress = false;
 470
 471        if (buffer->write_in_progress) {
 472                struct configfs_fragment *frag = to_frag(file);
 473                buffer->write_in_progress = false;
 474
 475                down_read(&frag->frag_sem);
 476                if (!frag->frag_dead) {
 477                        /* result of ->release() is ignored */
 478                        buffer->bin_attr->write(buffer->item,
 479                                        buffer->bin_buffer,
 480                                        buffer->bin_buffer_size);
 481                }
 482                up_read(&frag->frag_sem);
 483        }
 484
 485        vfree(buffer->bin_buffer);
 486        buffer->bin_buffer = NULL;
 487        buffer->bin_buffer_size = 0;
 488        buffer->needs_read_fill = 1;
 489
 490        configfs_release(inode, file);
 491        return 0;
 492}
 493
 494
 495const struct file_operations configfs_file_operations = {
 496        .read           = configfs_read_file,
 497        .write          = configfs_write_file,
 498        .llseek         = generic_file_llseek,
 499        .open           = configfs_open_file,
 500        .release        = configfs_release,
 501};
 502
 503const struct file_operations configfs_bin_file_operations = {
 504        .read           = configfs_read_bin_file,
 505        .write          = configfs_write_bin_file,
 506        .llseek         = NULL,         /* bin file is not seekable */
 507        .open           = configfs_open_bin_file,
 508        .release        = configfs_release_bin_file,
 509};
 510
 511/**
 512 *      configfs_create_file - create an attribute file for an item.
 513 *      @item:  item we're creating for.
 514 *      @attr:  atrribute descriptor.
 515 */
 516
 517int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
 518{
 519        struct dentry *dir = item->ci_dentry;
 520        struct configfs_dirent *parent_sd = dir->d_fsdata;
 521        umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
 522        int error = 0;
 523
 524        inode_lock_nested(d_inode(dir), I_MUTEX_NORMAL);
 525        error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode,
 526                                     CONFIGFS_ITEM_ATTR, parent_sd->s_frag);
 527        inode_unlock(d_inode(dir));
 528
 529        return error;
 530}
 531
 532/**
 533 *      configfs_create_bin_file - create a binary attribute file for an item.
 534 *      @item:  item we're creating for.
 535 *      @attr:  atrribute descriptor.
 536 */
 537
 538int configfs_create_bin_file(struct config_item *item,
 539                const struct configfs_bin_attribute *bin_attr)
 540{
 541        struct dentry *dir = item->ci_dentry;
 542        struct configfs_dirent *parent_sd = dir->d_fsdata;
 543        umode_t mode = (bin_attr->cb_attr.ca_mode & S_IALLUGO) | S_IFREG;
 544        int error = 0;
 545
 546        inode_lock_nested(dir->d_inode, I_MUTEX_NORMAL);
 547        error = configfs_make_dirent(parent_sd, NULL, (void *) bin_attr, mode,
 548                                     CONFIGFS_ITEM_BIN_ATTR, parent_sd->s_frag);
 549        inode_unlock(dir->d_inode);
 550
 551        return error;
 552}
 553