path: root/fs/read_write.c

/*
 *  linux/fs/read_write.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/slab.h> 
#include <linux/stat.h>
#include <linux/fcntl.h>
#include <linux/file.h>
#include <linux/uio.h>
#include <linux/fsnotify.h>
#include <linux/security.h>
#include <linux/module.h>
#include <linux/syscalls.h>
#include <linux/pagemap.h>
#include <linux/splice.h>
#include "read_write.h"

#include <asm/uaccess.h>
#include <asm/unistd.h>

const struct file_operations generic_ro_fops = {
	.llseek		= generic_file_llseek,
	.read		= do_sync_read,
	.aio_read	= generic_file_aio_read,
	.mmap		= generic_file_readonly_mmap,
	.splice_read	= generic_file_splice_read,
};

EXPORT_SYMBOL(generic_ro_fops);

static inline int unsigned_offsets(struct file *file)
{
	return file->f_mode & FMODE_UNSIGNED_OFFSET;
}

static loff_t lseek_execute(struct file *file, struct inode *inode,
		loff_t offset, loff_t maxsize)
{
	if (offset < 0 && !unsigned_offsets(file))
		return -EINVAL;
	if (offset > maxsize)
		return -EINVAL;

	if (offset != file->f_pos) {
		file->f_pos = offset;
		file->f_version = 0;
	}
	return offset;
}

/**
 * generic_file_llseek_size - generic llseek implementation for regular files
 * @file:	file structure to seek on
 * @offset:	file offset to seek to
 * @origin:	type of seek
 * @size:	max size of file system
 *
 * This is a variant of generic_file_llseek that allows passing in a custom
 * file size.
 *
 * Synchronization:
 * SEEK_SET and SEEK_END are unsynchronized (but atomic on 64bit platforms)
 * SEEK_CUR is synchronized against other SEEK_CURs, but not read/writes.
 * read/writes behave like SEEK_SET against seeks.
 */
loff_t
generic_file_llseek_size(struct file *file, loff_t offset, int origin,
		loff_t maxsize)
{
	struct inode *inode = file->f_mapping->host;

	switch (origin) {
	case SEEK_END:
		offset += i_size_read(inode);
		break;
	case SEEK_CUR:
		/*
		 * Here we special-case the lseek(fd, 0, SEEK_CUR)
		 * position-querying operation.  Avoid rewriting the "same"
		 * f_pos value back to the file because a concurrent read(),
		 * write() or lseek() might have altered it
		 */
		if (offset == 0)
			return file->f_pos;
		/*
		 * f_lock protects against read/modify/write race with other
		 * SEEK_CURs. Note that parallel writes and reads behave
		 * like SEEK_SET.
		 */
		spin_lock(&file->f_lock);
		offset = lseek_execute(file, inode, file->f_pos + offset,
				       maxsize);
		spin_unlock(&file->f_lock);
		return offset;
	case SEEK_DATA:
		/*
		 * In the generic case the entire file is data, so as long as
		 * offset isn't at the end of the file then the offset is data.
		 */
		if (offset >= i_size_read(inode))
			return -ENXIO;
		break;
	case SEEK_HOLE:
		/*
		 * There is a virtual hole at the end of the file, so as long as
		 * offset isn't i_size or larger, return i_size.
		 */
		if (offset >= i_size_read(inode))
			return -ENXIO;
		offset = i_size_read(inode);
		break;
	}

	return lseek_execute(file, inode, offset, maxsize);
}
EXPORT_SYMBOL(generic_file_llseek_size);

/**
 * generic_file_llseek - generic llseek implementation for regular files
 * @file:	file structure to seek on
 * @offset:	file offset to seek to
 * @origin:	type of seek
 *
 * This is a generic implemenation of ->llseek useable for all normal local
 * filesystems.  It just updates the file offset to the value specified by
 * @offset and @origin under i_mutex.
 */
loff_t generic_file_llseek(struct file *file, loff_t offset, int origin)
{
	struct inode *inode = file->f_mapping->host;

	return generic_file_llseek_size(file, offset, origin,
					inode->i_sb->s_maxbytes);
}
EXPORT_SYMBOL(generic_file_llseek);

/**
 * noop_llseek - No Operation Performed llseek implementation
 * @file:	file structure to seek on
 * @offset:	file offset to seek to
 * @origin:	type of seek
 *
 * This is an implementation of ->llseek useable for the rare special case when
 * userspace expects the seek to succeed but the (device) file is actually not
 * able to perform the seek. In this case you use noop_llseek() instead of
 * falling back to the default implementation of ->llseek.
 */
loff_t noop_llseek(struct file *file, loff_t offset, int origin)
{
	return file->f_pos;
}
EXPORT_SYMBOL(noop_llseek);

loff_t no_llseek(struct file *file, loff_t offset, int origin)
{
	return -ESPIPE;
}
EXPORT_SYMBOL(no_llseek);

loff_t default_llseek(struct file *file, loff_t offset, int origin)
{
	struct inode *inode = file->f_path.dentry->d_inode;
	loff_t retval;

	mutex_lock(&inode->i_mutex);
	switch (origin) {
		case SEEK_END:
			offset += i_size_read(inode);
			break;
		case SEEK_CUR:
			if (offset == 0) {
				retval = file->f_pos;
				goto out;
			}
			offset += file->f_pos;
			break;
		case SEEK_DATA:
			/*
			 * In the generic case the entire file is data, so as