自学教程：C++ unsigned_offsets函数代码示例

int rw_verify_area(int read_write, struct file *file, const loff_t *ppos, size_t count){	struct inode *inode;	loff_t pos;	int retval = -EINVAL;	inode = file_inode(file);	if (unlikely((ssize_t) count < 0))		return retval;	pos = *ppos;	if (unlikely(pos < 0)) {		if (!unsigned_offsets(file))			return retval;		if (count >= -pos) /* both values are in 0..LLONG_MAX */			return -EOVERFLOW;	} else if (unlikely((loff_t) (pos + count) < 0)) {		if (!unsigned_offsets(file))			return retval;	}	if (unlikely(inode->i_flctx && mandatory_lock(inode))) {		retval = locks_mandatory_area(inode, file, pos, pos + count - 1,				read_write == READ ? F_RDLCK : F_WRLCK);		if (retval < 0)			return retval;	}	return security_file_permission(file,				read_write == READ ? MAY_READ : MAY_WRITE);}

/** * generic_file_llseek_unlocked - lockless generic llseek implementation * @file:	file structure to seek on * @offset:	file offset to seek to * @origin:	type of seek * * Updates the file offset to the value specified by @offset and @origin. * Locking must be provided by the caller. */loff_tgeneric_file_llseek_unlocked(struct file *file, loff_t offset, int origin){	struct inode *inode = file->f_mapping->host;	switch (origin) {	case SEEK_END:		offset += inode->i_size;		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;		offset += file->f_pos;		break;	}	if (offset < 0 && !unsigned_offsets(file))		return -EINVAL;	if (offset > inode->i_sb->s_maxbytes)		return -EINVAL;	/* Special lock needed here? */	if (offset != file->f_pos) {		file->f_pos = offset;		file->f_version = 0;	}	return offset;}

loff_t default_llseek(struct file *file, loff_t offset, int origin){	loff_t retval;	mutex_lock(&file->f_dentry->d_inode->i_mutex);	switch (origin) {		case SEEK_END:			offset += i_size_read(file->f_path.dentry->d_inode);			break;		case SEEK_CUR:			if (offset == 0) {				retval = file->f_pos;				goto out;			}			offset += file->f_pos;	}	retval = -EINVAL;	if (offset >= 0 || unsigned_offsets(file)) {		if (offset != file->f_pos) {			file->f_pos = offset;			file->f_version = 0;		}		retval = offset;	}out:	mutex_unlock(&file->f_dentry->d_inode->i_mutex);	return retval;}

loff_t default_llseek(struct file *file, loff_t offset, int whence){	struct inode *inode = file_inode(file);	loff_t retval;	mutex_lock(&inode->i_mutex);	switch (whence) {		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			 * long as offset isn't at the end of the file then the			 * offset is data.			 */			if (offset >= inode->i_size) {				retval = -ENXIO;				goto out;			}			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 >= inode->i_size) {				retval = -ENXIO;				goto out;			}			offset = inode->i_size;			break;	}	retval = -EINVAL;	if (offset >= 0 || unsigned_offsets(file)) {		if (offset != file->f_pos) {			file->f_pos = offset;			file->f_version = 0;#ifdef CONFIG_DCACHE_COMPLETENESS			/* if any lseek has happen, the directory cannot be			 * complete */			file->f_dir_gen--;#endif		}		retval = offset;	}out:	mutex_unlock(&inode->i_mutex);	return retval;}

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			 * long as offset isn't at the end of the file then the			 * offset is data.			 */			if (offset >= inode->i_size) {				retval = -ENXIO;				goto out;			}			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 >= inode->i_size) {				retval = -ENXIO;				goto out;			}			offset = inode->i_size;			break;	}	retval = -EINVAL;	if (offset >= 0 || unsigned_offsets(file)) {		if (offset != file->f_pos) {			file->f_pos = offset;			file->f_version = 0;		}		retval = offset;	}out:	mutex_unlock(&inode->i_mutex);	return retval;}

/** * vfs_setpos - update the file offset for lseek * @file:	file structure in question * @offset:	file offset to seek to * @maxsize:	maximum file size * * This is a low-level filesystem helper for updating the file offset to * the value specified by @offset if the given offset is valid and it is * not equal to the current file offset. * * Return the specified offset on success and -EINVAL on invalid offset. */loff_t vfs_setpos(struct file *file, 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;}

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;}

/** * vfs_setpos - update the file offset for lseek * @file:	file structure in question * @offset:	file offset to seek to * @maxsize:	maximum file size * * This is a low-level filesystem helper for updating the file offset to * the value specified by @offset if the given offset is valid and it is * not equal to the current file offset. * * Return the specified offset on success and -EINVAL on invalid offset. */loff_t vfs_setpos(struct file *file, 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;#ifdef CONFIG_DCACHE_COMPLETENESS		/* if any lseek has happen, the directory cannot be		 * complete */		file->f_dir_gen--;#endif	}	return offset;}

/** * vfs_setpos - update the file offset for lseek * @file:	file structure in question * @offset:	file offset to seek to * @maxsize:	maximum file size * * This is a low-level filesystem helper for updating the file offset to * the value specified by @offset if the given offset is valid and it is * not equal to the current file offset. * * Return the specified offset on success and -EINVAL on invalid offset. */loff_t vfs_setpos(struct file *file, 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;        //~ Tesina        if(file->f_flags & O_SESSION)        {            down_write(file->sess_so->sem);            file->sess_so->offset = file->f_pos;            printk("[VFS_SET_POS]Just fixed our file position in the session to %lld!/n", file->f_pos);            up_write(file->sess_so->sem);        }        file->f_version = 0;    }    return offset;}

//.........这里部分代码省略.........{	struct pagevec pvec;	int nr_pages;	if (whence != SEEK_DATA)		return 0;	/* find first dirty page index */	pagevec_init(&pvec, 0);	nr_pages = pagevec_lookup_tag(&pvec, mapping, &pgofs,					PAGECACHE_TAG_DIRTY, 1);	pgofs = nr_pages ? pvec.pages[0]->index : LONG_MAX;	pagevec_release(&pvec);	return pgofs;}static bool __found_offset(block_t blkaddr, pgoff_t dirty, pgoff_t pgofs,							int whence){	switch (whence) {	case SEEK_DATA:		if ((blkaddr == NEW_ADDR && dirty == pgofs) ||			(blkaddr != NEW_ADDR && blkaddr != NULL_ADDR))			return true;		break;	case SEEK_HOLE:		if (blkaddr == NULL_ADDR)			return true;		break;	}	return false;}static inline int unsigned_offsets(struct file *file){	return file->f_mode & FMODE_UNSIGNED_OFFSET;}static loff_t vfs_setpos(struct file *file, 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;}static loff_t f2fs_seek_block(struct file *file, loff_t offset, int whence){	struct inode *inode = file->f_mapping->host;	loff_t maxbytes = inode->i_sb->s_maxbytes;	struct dnode_of_data dn;	pgoff_t pgofs, end_offset, dirty;	loff_t data_ofs = offset;	loff_t isize;	int err = 0;	mutex_lock(&inode->i_mutex);	isize = i_size_read(inode);	if (offset >= isize)