swh:1:snp:3c665ee4f67729f27f2e40193ab88e7298cf0fef
Tip revision: bb6d3fb354c5ee8d6bde2d576eb7220ea09862b9 authored by Linus Torvalds on 10 February 2020, 00:08:48 UTC
Linux 5.6-rc1
Linux 5.6-rc1
Tip revision: bb6d3fb
file.c
// SPDX-License-Identifier: GPL-2.0-or-later
/* -*- mode: c; c-basic-offset: 8; -*-
* vim: noexpandtab sw=8 ts=8 sts=0:
*
* file.c - operations for regular (text) files.
*
* 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;
int cb_max_size;
struct config_item *item;
struct module *owner;
union {
struct configfs_attribute *attr;
struct configfs_bin_attribute *bin_attr;
};
};
static inline struct configfs_fragment *to_frag(struct file *file)
{
struct configfs_dirent *sd = file->f_path.dentry->d_fsdata;
return sd->s_frag;
}
static int fill_read_buffer(struct file *file, struct configfs_buffer *buffer)
{
struct configfs_fragment *frag = to_frag(file);
ssize_t count = -ENOENT;
if (!buffer->page)
buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
if (!buffer->page)
return -ENOMEM;
down_read(&frag->frag_sem);
if (!frag->frag_dead)
count = buffer->attr->show(buffer->item, buffer->page);
up_read(&frag->frag_sem);
if (count < 0)
return count;
if (WARN_ON_ONCE(count > (ssize_t)SIMPLE_ATTR_SIZE))
return -EIO;
buffer->needs_read_fill = 0;
buffer->count = count;
return 0;
}
/**
* 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) {
retval = fill_read_buffer(file, buffer);
if (retval)
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_fragment *frag = to_frag(file);
struct configfs_buffer *buffer = file->private_data;
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 */
down_read(&frag->frag_sem);
if (!frag->frag_dead)
len = buffer->bin_attr->read(buffer->item, NULL, 0);
else
len = -ENOENT;
up_read(&frag->frag_sem);
if (len <= 0) {
retval = len;
goto out;
}
/* do not exceed the maximum value */
if (buffer->cb_max_size && len > buffer->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 */
down_read(&frag->frag_sem);
if (!frag->frag_dead)
len = buffer->bin_attr->read(buffer->item,
buffer->bin_buffer, len);
else
len = -ENOENT;
up_read(&frag->frag_sem);
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;
}
static int
flush_write_buffer(struct file *file, struct configfs_buffer *buffer, size_t count)
{
struct configfs_fragment *frag = to_frag(file);
int res = -ENOENT;
down_read(&frag->frag_sem);
if (!frag->frag_dead)
res = buffer->attr->store(buffer->item, buffer->page, count);
up_read(&frag->frag_sem);
return res;
}
/**
* 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, 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;
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 (buffer->cb_max_size &&
*ppos + count > buffer->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 __configfs_open_file(struct inode *inode, struct file *file, int type)
{
struct dentry *dentry = file->f_path.dentry;
struct configfs_fragment *frag = to_frag(file);
struct configfs_attribute *attr;
struct configfs_buffer *buffer;
int error;
error = -ENOMEM;
buffer = kzalloc(sizeof(struct configfs_buffer), GFP_KERNEL);
if (!buffer)
goto out;
error = -ENOENT;
down_read(&frag->frag_sem);
if (unlikely(frag->frag_dead))
goto out_free_buffer;
error = -EINVAL;
buffer->item = to_item(dentry->d_parent);
if (!buffer->item)
goto out_free_buffer;
attr = to_attr(dentry);
if (!attr)
goto out_put_item;
if (type & CONFIGFS_ITEM_BIN_ATTR) {
buffer->bin_attr = to_bin_attr(dentry);
buffer->cb_max_size = buffer->bin_attr->cb_max_size;
} else {
buffer->attr = attr;
}
buffer->owner = attr->ca_owner;
/* Grab the module reference for this attribute if we have one */
error = -ENODEV;
if (!try_module_get(buffer->owner))
goto out_put_item;
error = -EACCES;
if (!buffer->item->ci_type)
goto out_put_module;
buffer->ops = buffer->item->ci_type->ct_item_ops;
/* 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 out_put_module;
if ((type & CONFIGFS_ITEM_ATTR) && !attr->store)
goto out_put_module;
if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->write)
goto out_put_module;
}
/* 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 out_put_module;
if ((type & CONFIGFS_ITEM_ATTR) && !attr->show)
goto out_put_module;
if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->read)
goto out_put_module;
}
mutex_init(&buffer->mutex);
buffer->needs_read_fill = 1;
buffer->read_in_progress = false;
buffer->write_in_progress = false;
file->private_data = buffer;
up_read(&frag->frag_sem);
return 0;
out_put_module:
module_put(buffer->owner);
out_put_item:
config_item_put(buffer->item);
out_free_buffer:
up_read(&frag->frag_sem);
kfree(buffer);
out:
return error;
}
static int configfs_release(struct inode *inode, struct file *filp)
{
struct configfs_buffer *buffer = filp->private_data;
module_put(buffer->owner);
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 __configfs_open_file(inode, filp, CONFIGFS_ITEM_ATTR);
}
static int configfs_open_bin_file(struct inode *inode, struct file *filp)
{
return __configfs_open_file(inode, filp, CONFIGFS_ITEM_BIN_ATTR);
}
static int configfs_release_bin_file(struct inode *inode, struct file *file)
{
struct configfs_buffer *buffer = file->private_data;
buffer->read_in_progress = false;
if (buffer->write_in_progress) {
struct configfs_fragment *frag = to_frag(file);
buffer->write_in_progress = false;
down_read(&frag->frag_sem);
if (!frag->frag_dead) {
/* result of ->release() is ignored */
buffer->bin_attr->write(buffer->item,
buffer->bin_buffer,
buffer->bin_buffer_size);
}
up_read(&frag->frag_sem);
/* vfree on NULL is safe */
vfree(buffer->bin_buffer);
buffer->bin_buffer = NULL;
buffer->bin_buffer_size = 0;
buffer->needs_read_fill = 1;
}
configfs_release(inode, file);
return 0;
}
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, parent_sd->s_frag);
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, parent_sd->s_frag);
inode_unlock(dir->d_inode);
return error;
}