Merge tag 'for-linus-20180929' of git://git.kernel.dk/linux-block

[linux-2.6/btrfs-unstable.git] / fs / configfs / file.c

/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * file.c - operations for regular (text) files.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 *
 * Based on sysfs:
 *      sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
 *
 * configfs Copyright (C) 2005 Oracle.  All rights reserved.
 */

#include <linux/fs.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/mutex.h>
#include <linux/vmalloc.h>
#include <linux/uaccess.h>

#include <linux/configfs.h>
#include "configfs_internal.h"

/*
 * A simple attribute can only be 4096 characters.  Why 4k?  Because the
 * original code limited it to PAGE_SIZE.  That's a bad idea, though,
 * because an attribute of 16k on ia64 won't work on x86.  So we limit to
 * 4k, our minimum common page size.
 */
#define SIMPLE_ATTR_SIZE 4096

struct configfs_buffer {
        size_t                  count;
        loff_t                  pos;
        char                    * page;
        struct configfs_item_operations * ops;
        struct mutex            mutex;
        int                     needs_read_fill;
        bool                    read_in_progress;
        bool                    write_in_progress;
        char                    *bin_buffer;
        int                     bin_buffer_size;
};


/**
 *      fill_read_buffer - allocate and fill buffer from item.
 *      @dentry:        dentry pointer.
 *      @buffer:        data buffer for file.
 *
 *      Allocate @buffer->page, if it hasn't been already, then call the
 *      config_item's show() method to fill the buffer with this attribute's
 *      data.
 *      This is called only once, on the file's first read.
 */
static int fill_read_buffer(struct dentry * dentry, struct configfs_buffer * buffer)
{
        struct configfs_attribute * attr = to_attr(dentry);
        struct config_item * item = to_item(dentry->d_parent);
        int ret = 0;
        ssize_t count;

        if (!buffer->page)
                buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
        if (!buffer->page)
                return -ENOMEM;

        count = attr->show(item, buffer->page);

        BUG_ON(count > (ssize_t)SIMPLE_ATTR_SIZE);
        if (count >= 0) {
                buffer->needs_read_fill = 0;
                buffer->count = count;
        } else
                ret = count;
        return ret;
}

/**
 *      configfs_read_file - read an attribute.
 *      @file:  file pointer.
 *      @buf:   buffer to fill.
 *      @count: number of bytes to read.
 *      @ppos:  starting offset in file.
 *
 *      Userspace wants to read an attribute file. The attribute descriptor
 *      is in the file's ->d_fsdata. The target item is in the directory's
 *      ->d_fsdata.
 *
 *      We call fill_read_buffer() to allocate and fill the buffer from the
 *      item's show() method exactly once (if the read is happening from
 *      the beginning of the file). That should fill the entire buffer with
 *      all the data the item has to offer for that attribute.
 *      We then call flush_read_buffer() to copy the buffer to userspace
 *      in the increments specified.
 */

static ssize_t
configfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
        struct configfs_buffer * buffer = file->private_data;
        ssize_t retval = 0;

        mutex_lock(&buffer->mutex);
        if (buffer->needs_read_fill) {
                if ((retval = fill_read_buffer(file->f_path.dentry,buffer)))
                        goto out;
        }
        pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",
                 __func__, count, *ppos, buffer->page);
        retval = simple_read_from_buffer(buf, count, ppos, buffer->page,
                                         buffer->count);
out:
        mutex_unlock(&buffer->mutex);
        return retval;
}

/**
 *      configfs_read_bin_file - read a binary attribute.
 *      @file:  file pointer.
 *      @buf:   buffer to fill.
 *      @count: number of bytes to read.
 *      @ppos:  starting offset in file.
 *
 *      Userspace wants to read a binary attribute file. The attribute
 *      descriptor is in the file's ->d_fsdata. The target item is in the
 *      directory's ->d_fsdata.
 *
 *      We check whether we need to refill the buffer. If so we will
 *      call the attributes' attr->read() twice. The first time we
 *      will pass a NULL as a buffer pointer, which the attributes' method
 *      will use to return the size of the buffer required. If no error
 *      occurs we will allocate the buffer using vmalloc and call
 *      attr->read() again passing that buffer as an argument.
 *      Then we just copy to user-space using simple_read_from_buffer.
 */

static ssize_t
configfs_read_bin_file(struct file *file, char __user *buf,
                       size_t count, loff_t *ppos)
{
        struct configfs_buffer *buffer = file->private_data;
        struct dentry *dentry = file->f_path.dentry;
        struct config_item *item = to_item(dentry->d_parent);
        struct configfs_bin_attribute *bin_attr = to_bin_attr(dentry);
        ssize_t retval = 0;
        ssize_t len = min_t(size_t, count, PAGE_SIZE);

        mutex_lock(&buffer->mutex);

        /* we don't support switching read/write modes */
        if (buffer->write_in_progress) {
                retval = -ETXTBSY;
                goto out;
        }
        buffer->read_in_progress = true;

        if (buffer->needs_read_fill) {
                /* perform first read with buf == NULL to get extent */
                len = bin_attr->read(item, NULL, 0);
                if (len <= 0) {
                        retval = len;
                        goto out;
                }

                /* do not exceed the maximum value */
                if (bin_attr->cb_max_size && len > bin_attr->cb_max_size) {
                        retval = -EFBIG;
                        goto out;
                }

                buffer->bin_buffer = vmalloc(len);
                if (buffer->bin_buffer == NULL) {
                        retval = -ENOMEM;
                        goto out;
                }
                buffer->bin_buffer_size = len;

                /* perform second read to fill buffer */
                len = bin_attr->read(item, buffer->bin_buffer, len);
                if (len < 0) {
                        retval = len;
                        vfree(buffer->bin_buffer);
                        buffer->bin_buffer_size = 0;
                        buffer->bin_buffer = NULL;
                        goto out;
                }

                buffer->needs_read_fill = 0;
        }

        retval = simple_read_from_buffer(buf, count, ppos, buffer->bin_buffer,
                                        buffer->bin_buffer_size);
out:
        mutex_unlock(&buffer->mutex);
        return retval;
}


/**
 *      fill_write_buffer - copy buffer from userspace.
 *      @buffer:        data buffer for file.
 *      @buf:           data from user.
 *      @count:         number of bytes in @userbuf.
 *
 *      Allocate @buffer->page if it hasn't been already, then
 *      copy the user-supplied buffer into it.
 */

static int
fill_write_buffer(struct configfs_buffer * buffer, const char __user * buf, size_t count)
{
        int error;

        if (!buffer->page)
                buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
        if (!buffer->page)
                return -ENOMEM;

        if (count >= SIMPLE_ATTR_SIZE)
                count = SIMPLE_ATTR_SIZE - 1;
        error = copy_from_user(buffer->page,buf,count);
        buffer->needs_read_fill = 1;
        /* if buf is assumed to contain a string, terminate it by \0,
         * so e.g. sscanf() can scan the string easily */
        buffer->page[count] = 0;
        return error ? -EFAULT : count;
}


/**
 *      flush_write_buffer - push buffer to config_item.
 *      @dentry:        dentry to the attribute
 *      @buffer:        data buffer for file.
 *      @count:         number of bytes
 *
 *      Get the correct pointers for the config_item and the attribute we're
 *      dealing with, then call the store() method for the attribute,
 *      passing the buffer that we acquired in fill_write_buffer().
 */

static int
flush_write_buffer(struct dentry * dentry, struct configfs_buffer * buffer, size_t count)
{
        struct configfs_attribute * attr = to_attr(dentry);
        struct config_item * item = to_item(dentry->d_parent);

        return attr->store(item, buffer->page, count);
}


/**
 *      configfs_write_file - write an attribute.
 *      @file:  file pointer
 *      @buf:   data to write
 *      @count: number of bytes
 *      @ppos:  starting offset
 *
 *      Similar to configfs_read_file(), though working in the opposite direction.
 *      We allocate and fill the data from the user in fill_write_buffer(),
 *      then push it to the config_item in flush_write_buffer().
 *      There is no easy way for us to know if userspace is only doing a partial
 *      write, so we don't support them. We expect the entire buffer to come
 *      on the first write.
 *      Hint: if you're writing a value, first read the file, modify only the
 *      the value you're changing, then write entire buffer back.
 */

static ssize_t
configfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
{
        struct configfs_buffer * buffer = file->private_data;
        ssize_t len;

        mutex_lock(&buffer->mutex);
        len = fill_write_buffer(buffer, buf, count);
        if (len > 0)
                len = flush_write_buffer(file->f_path.dentry, buffer, len);
        if (len > 0)
                *ppos += len;
        mutex_unlock(&buffer->mutex);
        return len;
}

/**
 *      configfs_write_bin_file - write a binary attribute.
 *      @file:  file pointer
 *      @buf:   data to write
 *      @count: number of bytes
 *      @ppos:  starting offset
 *
 *      Writing to a binary attribute file is similar to a normal read.
 *      We buffer the consecutive writes (binary attribute files do not
 *      support lseek) in a continuously growing buffer, but we don't
 *      commit until the close of the file.
 */

static ssize_t
configfs_write_bin_file(struct file *file, const char __user *buf,
                        size_t count, loff_t *ppos)
{
        struct configfs_buffer *buffer = file->private_data;
        struct dentry *dentry = file->f_path.dentry;
        struct configfs_bin_attribute *bin_attr = to_bin_attr(dentry);
        void *tbuf = NULL;
        ssize_t len;

        mutex_lock(&buffer->mutex);

        /* we don't support switching read/write modes */
        if (buffer->read_in_progress) {
                len = -ETXTBSY;
                goto out;
        }
        buffer->write_in_progress = true;

        /* buffer grows? */
        if (*ppos + count > buffer->bin_buffer_size) {

                if (bin_attr->cb_max_size &&
                        *ppos + count > bin_attr->cb_max_size) {
                        len = -EFBIG;
                        goto out;
                }

                tbuf = vmalloc(*ppos + count);
                if (tbuf == NULL) {
                        len = -ENOMEM;
                        goto out;
                }

                /* copy old contents */
                if (buffer->bin_buffer) {
                        memcpy(tbuf, buffer->bin_buffer,
                                buffer->bin_buffer_size);
                        vfree(buffer->bin_buffer);
                }

                /* clear the new area */
                memset(tbuf + buffer->bin_buffer_size, 0,
                        *ppos + count - buffer->bin_buffer_size);
                buffer->bin_buffer = tbuf;
                buffer->bin_buffer_size = *ppos + count;
        }

        len = simple_write_to_buffer(buffer->bin_buffer,
                        buffer->bin_buffer_size, ppos, buf, count);
out:
        mutex_unlock(&buffer->mutex);
        return len;
}

static int check_perm(struct inode * inode, struct file * file, int type)
{
        struct config_item *item = configfs_get_config_item(file->f_path.dentry->d_parent);
        struct configfs_attribute * attr = to_attr(file->f_path.dentry);
        struct configfs_bin_attribute *bin_attr = NULL;
        struct configfs_buffer * buffer;
        struct configfs_item_operations * ops = NULL;
        int error = 0;

        if (!item || !attr)
                goto Einval;

        if (type & CONFIGFS_ITEM_BIN_ATTR)
                bin_attr = to_bin_attr(file->f_path.dentry);

        /* Grab the module reference for this attribute if we have one */
        if (!try_module_get(attr->ca_owner)) {
                error = -ENODEV;
                goto Done;
        }

        if (item->ci_type)
                ops = item->ci_type->ct_item_ops;
        else
                goto Eaccess;

        /* File needs write support.
         * The inode's perms must say it's ok,
         * and we must have a store method.
         */
        if (file->f_mode & FMODE_WRITE) {
                if (!(inode->i_mode & S_IWUGO))
                        goto Eaccess;

                if ((type & CONFIGFS_ITEM_ATTR) && !attr->store)
                        goto Eaccess;

                if ((type & CONFIGFS_ITEM_BIN_ATTR) && !bin_attr->write)
                        goto Eaccess;
        }

        /* File needs read support.
         * The inode's perms must say it's ok, and we there
         * must be a show method for it.
         */
        if (file->f_mode & FMODE_READ) {
                if (!(inode->i_mode & S_IRUGO))
                        goto Eaccess;

                if ((type & CONFIGFS_ITEM_ATTR) && !attr->show)
                        goto Eaccess;

                if ((type & CONFIGFS_ITEM_BIN_ATTR) && !bin_attr->read)
                        goto Eaccess;
        }

        /* No error? Great, allocate a buffer for the file, and store it
         * it in file->private_data for easy access.
         */
        buffer = kzalloc(sizeof(struct configfs_buffer),GFP_KERNEL);
        if (!buffer) {
                error = -ENOMEM;
                goto Enomem;
        }
        mutex_init(&buffer->mutex);
        buffer->needs_read_fill = 1;
        buffer->read_in_progress = false;
        buffer->write_in_progress = false;
        buffer->ops = ops;
        file->private_data = buffer;
        goto Done;

 Einval:
        error = -EINVAL;
        goto Done;
 Eaccess:
        error = -EACCES;
 Enomem:
        module_put(attr->ca_owner);
 Done:
        if (error && item)
                config_item_put(item);
        return error;
}

static int configfs_release(struct inode *inode, struct file *filp)
{
        struct config_item * item = to_item(filp->f_path.dentry->d_parent);
        struct configfs_attribute * attr = to_attr(filp->f_path.dentry);
        struct module * owner = attr->ca_owner;
        struct configfs_buffer * buffer = filp->private_data;

        if (item)
                config_item_put(item);
        /* After this point, attr should not be accessed. */
        module_put(owner);

        if (buffer) {
                if (buffer->page)
                        free_page((unsigned long)buffer->page);
                mutex_destroy(&buffer->mutex);
                kfree(buffer);
        }
        return 0;
}

static int configfs_open_file(struct inode *inode, struct file *filp)
{
        return check_perm(inode, filp, CONFIGFS_ITEM_ATTR);
}

static int configfs_open_bin_file(struct inode *inode, struct file *filp)
{
        return check_perm(inode, filp, CONFIGFS_ITEM_BIN_ATTR);
}

static int configfs_release_bin_file(struct inode *inode, struct file *filp)
{
        struct configfs_buffer *buffer = filp->private_data;
        struct dentry *dentry = filp->f_path.dentry;
        struct config_item *item = to_item(dentry->d_parent);
        struct configfs_bin_attribute *bin_attr = to_bin_attr(dentry);
        ssize_t len = 0;
        int ret;

        buffer->read_in_progress = false;

        if (buffer->write_in_progress) {
                buffer->write_in_progress = false;

                len = bin_attr->write(item, buffer->bin_buffer,
                                buffer->bin_buffer_size);

                /* vfree on NULL is safe */
                vfree(buffer->bin_buffer);
                buffer->bin_buffer = NULL;
                buffer->bin_buffer_size = 0;
                buffer->needs_read_fill = 1;
        }

        ret = configfs_release(inode, filp);
        if (len < 0)
                return len;
        return ret;
}


const struct file_operations configfs_file_operations = {
        .read           = configfs_read_file,
        .write          = configfs_write_file,
        .llseek         = generic_file_llseek,
        .open           = configfs_open_file,
        .release        = configfs_release,
};

const struct file_operations configfs_bin_file_operations = {
        .read           = configfs_read_bin_file,
        .write          = configfs_write_bin_file,
        .llseek         = NULL,         /* bin file is not seekable */
        .open           = configfs_open_bin_file,
        .release        = configfs_release_bin_file,
};

/**
 *      configfs_create_file - create an attribute file for an item.
 *      @item:  item we're creating for.
 *      @attr:  atrribute descriptor.
 */

int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
{
        struct dentry *dir = item->ci_dentry;
        struct configfs_dirent *parent_sd = dir->d_fsdata;
        umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
        int error = 0;

        inode_lock_nested(d_inode(dir), I_MUTEX_NORMAL);
        error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode,
                                     CONFIGFS_ITEM_ATTR);
        inode_unlock(d_inode(dir));

        return error;
}

/**
 *      configfs_create_bin_file - create a binary attribute file for an item.
 *      @item:  item we're creating for.
 *      @attr:  atrribute descriptor.
 */

int configfs_create_bin_file(struct config_item *item,
                const struct configfs_bin_attribute *bin_attr)
{
        struct dentry *dir = item->ci_dentry;
        struct configfs_dirent *parent_sd = dir->d_fsdata;
        umode_t mode = (bin_attr->cb_attr.ca_mode & S_IALLUGO) | S_IFREG;
        int error = 0;

        inode_lock_nested(dir->d_inode, I_MUTEX_NORMAL);
        error = configfs_make_dirent(parent_sd, NULL, (void *) bin_attr, mode,
                                     CONFIGFS_ITEM_BIN_ATTR);
        inode_unlock(dir->d_inode);

        return error;
}