file_operations_bsfs.c File Reference

Implementation of file-level operations in the BSFS file system. More...

Functions
int	open_file (FILE *disk, btree_handle_t *inode_tree, uint32_t inode_number, file_t *out_file)
	Opens a file by loading its inode into memory.
int	close_file (FILE *disk, btree_handle_t *inode_tree, file_t *file)
	Closes an open file and writes back its inode.
int32_t	seek_file (file_t *file, int32_t offset, int whence)
	Moves the file position indicator to a new location.
int	read_file (FILE *disk, btree_handle_t *handle, file_t *file, uint8_t *buffer, uint32_t size)
	Reads data from an open file into a buffer.
int	truncate_file (FILE *disk, superblock_t *sb, btree_handle_t *bspan_tree, file_t *f, uint32_t new_size)
	Truncates a file from a given byte offset, removing its excess data blocks.
int	write_file (FILE *disk, superblock_t *sb, btree_handle_t *bspan_tree, file_t *f, const uint8_t *buffer, uint32_t size, int truncate)
	Writes data to a file, with optional truncation.

Detailed Description

Implementation of file-level operations in the BSFS file system.

This file provides functions to manipulate files, including opening, closing, reading, writing, and seeking, by utilizing inodes and B-tree-based address mapping. Files are loaded into memory as file_t structures which manage stateful access.

Function Documentation

close_file()

int close_file	(	FILE *	disk,
		btree_handle_t *	inode_tree,
		file_t *	file )

Closes an open file and writes back its inode.

This function persists any changes made to the file's inode (e.g., size updates) by writing it back into the inode B-tree.

Parameters

disk	Pointer to the open disk file.
inode_tree	Pointer to the B-tree of inodes.
file	Pointer to the file_t structure representing the open file.

Returns

0 on success, -1 on failure.

open_file()

int open_file	(	FILE *	disk,
		btree_handle_t *	inode_tree,
		uint32_t	inode_number,
		file_t *	out_file )

Opens a file by loading its inode into memory.

This function looks up the specified inode number in the inode B-tree, and populates the file_t structure with its contents.

Parameters

disk	Pointer to the open disk file.
inode_tree	Pointer to the B-tree of inodes.
inode_number	The inode number of the file to open.
out_file	Pointer to the file_t structure to populate.

Returns

0 on success, -1 on failure (e.g., inode not found).

read_file()

int read_file	(	FILE *	disk,
		btree_handle_t *	handle,
		file_t *	file,
		uint8_t *	buffer,
		uint32_t	size )

Reads data from an open file into a buffer.

Reads up to size bytes from the current position in the file into buffer. The function checks direct bspan_t spans in the inode first, then falls back to the B-tree for additional block mappings. If a block is not mapped, it is treated as zeroed.

Parameters

disk	Pointer to the disk image file.
handle	B-tree handle used for indirect block mapping.
file	Open file structure (with inode and current position).
buffer	Buffer to read data into.
size	Number of bytes to read.

Returns

Number of bytes successfully read.

seek_file()

int32_t seek_file	(	file_t *	file,
		int32_t	offset,
		int	whence )

Moves the file position indicator to a new location.

This function adjusts the pos field of the file_t structure, which determines the current read/write position in the file.

The behavior of the seek operation depends on the whence parameter:

• SEEK_SET: position is set to offset
• SEEK_CUR: position is moved by offset from the current position
• SEEK_END: position is set to file size + offset

Parameters

file	Pointer to the open file structure.
offset	Number of bytes to move the position indicator.
whence	Starting point for the offset: SEEK_SET, SEEK_CUR, SEEK_END.

Returns

The new file position on success, or -1 on failure.

truncate_file()

int truncate_file	(	FILE *	disk,
		superblock_t *	sb,
		btree_handle_t *	bspan_tree,
		file_t *	f,
		uint32_t	new_size )

Truncates a file from a given byte offset, removing its excess data blocks.

This function removes all bspan mappings beyond the given logical file size, effectively truncating the file and freeing corresponding disk blocks.

It updates the file's inode size and adjusts the read/write position if needed.

Parameters

disk	Pointer to the open disk file.
sb	Pointer to the superblock structure.
bspan_tree	B-tree handle that maps logical file blocks to disk blocks.
f	Pointer to the open file structure.
new_size	The new desired file size in bytes.

Returns

0 on success, -1 on error.

write_file()

int write_file	(	FILE *	disk,
		superblock_t *	sb,
		btree_handle_t *	bspan_tree,
		file_t *	f,
		const uint8_t *	buffer,
		uint32_t	size,
		int	truncate )

Writes data to a file, with optional truncation.

This function writes size bytes from buffer into the file starting at f->pos. It optionally truncates the file from that position before writing, based on the truncate flag:

• truncate == 0: overwrite data starting at f->pos, preserve what's after.
• truncate == 1: remove all data after f->pos before writing.
• If f->pos == inode.size, this acts as append (with or without truncation).

Parameters

disk	Pointer to the open disk file.
sb	Pointer to the superblock (for allocation and deallocation).
bspan_tree	B-tree handle mapping logical to physical blocks.
f	Pointer to the open file structure.
buffer	Pointer to the data to write.
size	Number of bytes to write.
truncate	1 to truncate after position before writing, 0 to preserve.

Returns

Number of bytes written, or -1 on error.