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#include <linux/uio.h>
  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
  80static ssize_t configfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
  81{
  82        struct file *file = iocb->ki_filp;
  83        struct configfs_buffer *buffer = file->private_data;
  84        ssize_t retval = 0;
  85
  86        mutex_lock(&buffer->mutex);
  87        if (buffer->needs_read_fill) {
  88                retval = fill_read_buffer(file, buffer);
  89                if (retval)
  90                        goto out;
  91        }
  92        pr_debug("%s: count = %zd, pos = %lld, buf = %s\n",
  93                 __func__, iov_iter_count(to), iocb->ki_pos, buffer->page);
  94        if (iocb->ki_pos >= buffer->count)
  95                goto out;
  96        retval = copy_to_iter(buffer->page + iocb->ki_pos,
  97                              buffer->count - iocb->ki_pos, to);
  98        iocb->ki_pos += retval;
  99        if (retval == 0)
 100                retval = -EFAULT;
 101out:
 102        mutex_unlock(&buffer->mutex);
 103        return retval;
 104}
 105
 106static ssize_t configfs_bin_read_iter(struct kiocb *iocb, struct iov_iter *to)
 107{
 108        struct file *file = iocb->ki_filp;
 109        struct configfs_fragment *frag = to_frag(file);
 110        struct configfs_buffer *buffer = file->private_data;
 111        ssize_t retval = 0;
 112        ssize_t len;
 113
 114        mutex_lock(&buffer->mutex);
 115
 116        /* we don't support switching read/write modes */
 117        if (buffer->write_in_progress) {
 118                retval = -ETXTBSY;
 119                goto out;
 120        }
 121        buffer->read_in_progress = true;
 122
 123        if (buffer->needs_read_fill) {
 124                /* perform first read with buf == NULL to get extent */
 125                down_read(&frag->frag_sem);
 126                if (!frag->frag_dead)
 127                        len = buffer->bin_attr->read(buffer->item, NULL, 0);
 128                else
 129                        len = -ENOENT;
 130                up_read(&frag->frag_sem);
 131                if (len <= 0) {
 132                        retval = len;
 133                        goto out;
 134                }
 135
 136                /* do not exceed the maximum value */
 137                if (buffer->cb_max_size && len > buffer->cb_max_size) {
 138                        retval = -EFBIG;
 139                        goto out;
 140                }
 141
 142                buffer->bin_buffer = vmalloc(len);
 143                if (buffer->bin_buffer == NULL) {
 144                        retval = -ENOMEM;
 145                        goto out;
 146                }
 147                buffer->bin_buffer_size = len;
 148
 149                /* perform second read to fill buffer */
 150                down_read(&frag->frag_sem);
 151                if (!frag->frag_dead)
 152                        len = buffer->bin_attr->read(buffer->item,
 153                                                     buffer->bin_buffer, len);
 154                else
 155                        len = -ENOENT;
 156                up_read(&frag->frag_sem);
 157                if (len < 0) {
 158                        retval = len;
 159                        vfree(buffer->bin_buffer);
 160                        buffer->bin_buffer_size = 0;
 161                        buffer->bin_buffer = NULL;
 162                        goto out;
 163                }
 164
 165                buffer->needs_read_fill = 0;
 166        }
 167
 168        if (iocb->ki_pos >= buffer->bin_buffer_size)
 169                goto out;
 170        retval = copy_to_iter(buffer->bin_buffer + iocb->ki_pos,
 171                              buffer->bin_buffer_size - iocb->ki_pos, to);
 172        iocb->ki_pos += retval;
 173        if (retval == 0)
 174                retval = -EFAULT;
 175out:
 176        mutex_unlock(&buffer->mutex);
 177        return retval;
 178}
 179
 180/* Fill @buffer with data coming from @from. */
 181static int fill_write_buffer(struct configfs_buffer *buffer,
 182                             struct iov_iter *from)
 183{
 184        int copied;
 185
 186        if (!buffer->page)
 187                buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
 188        if (!buffer->page)
 189                return -ENOMEM;
 190
 191        copied = copy_from_iter(buffer->page, SIMPLE_ATTR_SIZE - 1, from);
 192        buffer->needs_read_fill = 1;
 193        /* if buf is assumed to contain a string, terminate it by \0,
 194         * so e.g. sscanf() can scan the string easily */
 195        buffer->page[copied] = 0;
 196        return copied ? : -EFAULT;
 197}
 198
 199static int
 200flush_write_buffer(struct file *file, struct configfs_buffer *buffer, size_t count)
 201{
 202        struct configfs_fragment *frag = to_frag(file);
 203        int res = -ENOENT;
 204
 205        down_read(&frag->frag_sem);
 206        if (!frag->frag_dead)
 207                res = buffer->attr->store(buffer->item, buffer->page, count);
 208        up_read(&frag->frag_sem);
 209        return res;
 210}
 211
 212
 213/*
 214 * There is no easy way for us to know if userspace is only doing a partial
 215 * write, so we don't support them. We expect the entire buffer to come on the
 216 * first write.
 217 * Hint: if you're writing a value, first read the file, modify only the value
 218 * you're changing, then write entire buffer back.
 219 */
 220static ssize_t configfs_write_iter(struct kiocb *iocb, struct iov_iter *from)
 221{
 222        struct file *file = iocb->ki_filp;
 223        struct configfs_buffer *buffer = file->private_data;
 224        int len;
 225
 226        mutex_lock(&buffer->mutex);
 227        len = fill_write_buffer(buffer, from);
 228        if (len > 0)
 229                len = flush_write_buffer(file, buffer, len);
 230        if (len > 0)
 231                iocb->ki_pos += len;
 232        mutex_unlock(&buffer->mutex);
 233        return len;
 234}
 235
 236static ssize_t configfs_bin_write_iter(struct kiocb *iocb,
 237                                       struct iov_iter *from)
 238{
 239        struct file *file = iocb->ki_filp;
 240        struct configfs_buffer *buffer = file->private_data;
 241        void *tbuf = NULL;
 242        size_t end_offset;
 243        ssize_t len;
 244
 245        mutex_lock(&buffer->mutex);
 246
 247        /* we don't support switching read/write modes */
 248        if (buffer->read_in_progress) {
 249                len = -ETXTBSY;
 250                goto out;
 251        }
 252        buffer->write_in_progress = true;
 253
 254        /* buffer grows? */
 255        end_offset = iocb->ki_pos + iov_iter_count(from);
 256        if (end_offset > buffer->bin_buffer_size) {
 257                if (buffer->cb_max_size && end_offset > buffer->cb_max_size) {
 258                        len = -EFBIG;
 259                        goto out;
 260                }
 261
 262                tbuf = vmalloc(end_offset);
 263                if (tbuf == NULL) {
 264                        len = -ENOMEM;
 265                        goto out;
 266                }
 267
 268                /* copy old contents */
 269                if (buffer->bin_buffer) {
 270                        memcpy(tbuf, buffer->bin_buffer,
 271                                buffer->bin_buffer_size);
 272                        vfree(buffer->bin_buffer);
 273                }
 274
 275                /* clear the new area */
 276                memset(tbuf + buffer->bin_buffer_size, 0,
 277                        end_offset - buffer->bin_buffer_size);
 278                buffer->bin_buffer = tbuf;
 279                buffer->bin_buffer_size = end_offset;
 280        }
 281
 282        len = copy_from_iter(buffer->bin_buffer + iocb->ki_pos,
 283                             buffer->bin_buffer_size - iocb->ki_pos, from);
 284        iocb->ki_pos += len;
 285out:
 286        mutex_unlock(&buffer->mutex);
 287        return len ? : -EFAULT;
 288}
 289
 290static int __configfs_open_file(struct inode *inode, struct file *file, int type)
 291{
 292        struct dentry *dentry = file->f_path.dentry;
 293        struct configfs_fragment *frag = to_frag(file);
 294        struct configfs_attribute *attr;
 295        struct configfs_buffer *buffer;
 296        int error;
 297
 298        error = -ENOMEM;
 299        buffer = kzalloc(sizeof(struct configfs_buffer), GFP_KERNEL);
 300        if (!buffer)
 301                goto out;
 302
 303        error = -ENOENT;
 304        down_read(&frag->frag_sem);
 305        if (unlikely(frag->frag_dead))
 306                goto out_free_buffer;
 307
 308        error = -EINVAL;
 309        buffer->item = to_item(dentry->d_parent);
 310        if (!buffer->item)
 311                goto out_free_buffer;
 312
 313        attr = to_attr(dentry);
 314        if (!attr)
 315                goto out_free_buffer;
 316
 317        if (type & CONFIGFS_ITEM_BIN_ATTR) {
 318                buffer->bin_attr = to_bin_attr(dentry);
 319                buffer->cb_max_size = buffer->bin_attr->cb_max_size;
 320        } else {
 321                buffer->attr = attr;
 322        }
 323
 324        buffer->owner = attr->ca_owner;
 325        /* Grab the module reference for this attribute if we have one */
 326        error = -ENODEV;
 327        if (!try_module_get(buffer->owner))
 328                goto out_free_buffer;
 329
 330        error = -EACCES;
 331        if (!buffer->item->ci_type)
 332                goto out_put_module;
 333
 334        buffer->ops = buffer->item->ci_type->ct_item_ops;
 335
 336        /* File needs write support.
 337         * The inode's perms must say it's ok,
 338         * and we must have a store method.
 339         */
 340        if (file->f_mode & FMODE_WRITE) {
 341                if (!(inode->i_mode & S_IWUGO))
 342                        goto out_put_module;
 343                if ((type & CONFIGFS_ITEM_ATTR) && !attr->store)
 344                        goto out_put_module;
 345                if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->write)
 346                        goto out_put_module;
 347        }
 348
 349        /* File needs read support.
 350         * The inode's perms must say it's ok, and we there
 351         * must be a show method for it.
 352         */
 353        if (file->f_mode & FMODE_READ) {
 354                if (!(inode->i_mode & S_IRUGO))
 355                        goto out_put_module;
 356                if ((type & CONFIGFS_ITEM_ATTR) && !attr->show)
 357                        goto out_put_module;
 358                if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->read)
 359                        goto out_put_module;
 360        }
 361
 362        mutex_init(&buffer->mutex);
 363        buffer->needs_read_fill = 1;
 364        buffer->read_in_progress = false;
 365        buffer->write_in_progress = false;
 366        file->private_data = buffer;
 367        up_read(&frag->frag_sem);
 368        return 0;
 369
 370out_put_module:
 371        module_put(buffer->owner);
 372out_free_buffer:
 373        up_read(&frag->frag_sem);
 374        kfree(buffer);
 375out:
 376        return error;
 377}
 378
 379static int configfs_release(struct inode *inode, struct file *filp)
 380{
 381        struct configfs_buffer *buffer = filp->private_data;
 382
 383        module_put(buffer->owner);
 384        if (buffer->page)
 385                free_page((unsigned long)buffer->page);
 386        mutex_destroy(&buffer->mutex);
 387        kfree(buffer);
 388        return 0;
 389}
 390
 391static int configfs_open_file(struct inode *inode, struct file *filp)
 392{
 393        return __configfs_open_file(inode, filp, CONFIGFS_ITEM_ATTR);
 394}
 395
 396static int configfs_open_bin_file(struct inode *inode, struct file *filp)
 397{
 398        return __configfs_open_file(inode, filp, CONFIGFS_ITEM_BIN_ATTR);
 399}
 400
 401static int configfs_release_bin_file(struct inode *inode, struct file *file)
 402{
 403        struct configfs_buffer *buffer = file->private_data;
 404
 405        if (buffer->write_in_progress) {
 406                struct configfs_fragment *frag = to_frag(file);
 407
 408                down_read(&frag->frag_sem);
 409                if (!frag->frag_dead) {
 410                        /* result of ->release() is ignored */
 411                        buffer->bin_attr->write(buffer->item,
 412                                        buffer->bin_buffer,
 413                                        buffer->bin_buffer_size);
 414                }
 415                up_read(&frag->frag_sem);
 416        }
 417
 418        vfree(buffer->bin_buffer);
 419
 420        configfs_release(inode, file);
 421        return 0;
 422}
 423
 424
 425const struct file_operations configfs_file_operations = {
 426        .read_iter      = configfs_read_iter,
 427        .write_iter     = configfs_write_iter,
 428        .llseek         = generic_file_llseek,
 429        .open           = configfs_open_file,
 430        .release        = configfs_release,
 431};
 432
 433const struct file_operations configfs_bin_file_operations = {
 434        .read_iter      = configfs_bin_read_iter,
 435        .write_iter     = configfs_bin_write_iter,
 436        .llseek         = NULL,         /* bin file is not seekable */
 437        .open           = configfs_open_bin_file,
 438        .release        = configfs_release_bin_file,
 439};
 440
 441/**
 442 *      configfs_create_file - create an attribute file for an item.
 443 *      @item:  item we're creating for.
 444 *      @attr:  atrribute descriptor.
 445 */
 446
 447int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
 448{
 449        struct dentry *dir = item->ci_dentry;
 450        struct configfs_dirent *parent_sd = dir->d_fsdata;
 451        umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
 452        int error = 0;
 453
 454        inode_lock_nested(d_inode(dir), I_MUTEX_NORMAL);
 455        error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode,
 456                                     CONFIGFS_ITEM_ATTR, parent_sd->s_frag);
 457        inode_unlock(d_inode(dir));
 458
 459        return error;
 460}
 461
 462/**
 463 *      configfs_create_bin_file - create a binary attribute file for an item.
 464 *      @item:  item we're creating for.
 465 *      @bin_attr: atrribute descriptor.
 466 */
 467
 468int configfs_create_bin_file(struct config_item *item,
 469                const struct configfs_bin_attribute *bin_attr)
 470{
 471        struct dentry *dir = item->ci_dentry;
 472        struct configfs_dirent *parent_sd = dir->d_fsdata;
 473        umode_t mode = (bin_attr->cb_attr.ca_mode & S_IALLUGO) | S_IFREG;
 474        int error = 0;
 475
 476        inode_lock_nested(dir->d_inode, I_MUTEX_NORMAL);
 477        error = configfs_make_dirent(parent_sd, NULL, (void *) bin_attr, mode,
 478                                     CONFIGFS_ITEM_BIN_ATTR, parent_sd->s_frag);
 479        inode_unlock(dir->d_inode);
 480
 481        return error;
 482}
 483
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