spz-lab4/src/fs.c

#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <stdlib.h>

#include "print.h"
#include "fs.h"

#include "config.h"

const static int BLOCK_ADDRESSES_PER_INODE = (FS_BLOCK_SIZE-sizeof(int)*3) / sizeof(int);
const static int BLOCK_ADDRESSES_PER_INODE_EXTENSION = (FS_BLOCK_SIZE-sizeof(int)) / sizeof(int);
const static int DIRECTORY_RECORDS_PER_BLOCK = FS_BLOCK_SIZE / sizeof(struct fs_directory_record);


static char used_file_path[FS_MAX_DEVICE_FILE_NAME_LEN+1];
static int used_file_fd;
static int write_permitted;

static char fs_cwd[FS_MAX_PATH_LEN+1];
static unsigned int fs_cwd_inode_ptr;

static struct fs_file_description fs_file_descriptions[FS_MAX_OPEN_FD];


static int read_block(unsigned int block_no, void *data)
{
	if (lseek(used_file_fd, block_no * FS_BLOCK_SIZE, SEEK_SET) < 0) {
		pr_err("failed to seek to block %d (bs=%d) on device '%s'\n", block_no, FS_BLOCK_SIZE, used_file_path);
		return -1;
	}

	return read(used_file_fd, data, FS_BLOCK_SIZE);
}

static int write_block(unsigned int block_no, void *data)
{
	if (!write_permitted) {
		pr_err("write operations are prohibited\n");
		return -1;
	}

	if (lseek(used_file_fd, block_no * FS_BLOCK_SIZE, SEEK_SET) < 0) {
		pr_err("failed to seek to block %d (bs=%d) on device '%s'\n", block_no, FS_BLOCK_SIZE, used_file_path);
		return -1;
	}

	return write(used_file_fd, data, FS_BLOCK_SIZE);
}

static void mark_used(unsigned int block_no)
{
	struct fs_header fsh;
	read_block(0, (void *) &fsh);

	if (block_no > fsh.block_count) {
		pr_err("block %d is out of filesystem block range (%d)\n", block_no, fsh.block_count);
		return;
	}

	unsigned char bitmap_bit = 1 << (block_no & 0x7);
	unsigned int bitmap_block_offset = (block_no >> 3) % FS_BLOCK_SIZE;
	unsigned int bitmap_block_index = (block_no >> 3) / FS_BLOCK_SIZE;

	unsigned char bitmap_block[FS_BLOCK_SIZE];
	read_block(bitmap_block_index+1, (void *) bitmap_block);

	bitmap_block[bitmap_block_offset] |= bitmap_bit;

	// write changes to device
	write_block(bitmap_block_index+1, (void *) &bitmap_block);

	pr("Marked block_no=%d (block=%d, offset=%d, bit=%d) as used\n",
			block_no, bitmap_block_index, bitmap_block_offset, block_no & 0x7);
}

static void mark_free(unsigned int block_no)
{
	struct fs_header fsh;
	read_block(0, (void *) &fsh);

	if (block_no > fsh.block_count) {
		pr_err("block %d is out of fimesystem block range (%d)\n", block_no, fsh.block_count);
		return;
	}

	unsigned char bitmap_bit = 1 << (block_no & 0x7);
	unsigned int bitmap_block_offset = (block_no >> 3) % FS_BLOCK_SIZE;
	unsigned int bitmap_block_index = (block_no >> 3) / FS_BLOCK_SIZE;

	unsigned char bitmap_block[FS_BLOCK_SIZE];
	read_block(bitmap_block_index+1, (void *) bitmap_block);

	bitmap_block[bitmap_block_offset] &= ~bitmap_bit;

	// write changes to device
	write_block(bitmap_block_index+1, (void *) bitmap_block);

	pr("Marked block_no=%d (block=%d, offset=%d, bit=%d) as free\n",
			block_no, bitmap_block_index, bitmap_block_offset, bitmap_bit);
}

static int identify_fs(void)
{
	struct fs_header read_buf;
	{
		int read_amount = read_block(0, (void *) &read_buf);

		if (read_amount < 0) {
			pr_err("failed to read fs_header from storage device '%s'\n", used_file_path);
			return 0;
		}

		if (read_amount < FS_BLOCK_SIZE) {
			pr_warn("failed to read full block (read %d/%d bytes)\n", read_amount, FS_BLOCK_SIZE);
		} else if (read_amount == 0) {
			pr_err("storage device size is 0\n");
			return 0;
		}
	}

	if (read_buf.next_extension) {
		pr_info("identified filesystem version 0x%hhx with %d max inodes (on %d blocks), next header extension is at block 0x%x\n",
				read_buf.version, read_buf.max_inode_count, read_buf.block_count, read_buf.next_extension);
	} else {
		pr_info("identified filesystem version 0x%hhx with %d max inodes (on %d blocks), with no header extensions\n",
				read_buf.version, read_buf.max_inode_count, read_buf.block_count);
	}

	return read_buf.version;
}

static unsigned int find_free_block(void)
{
	unsigned int b = 0;

	struct fs_header fsh;
	read_block(0, (void *) &fsh);

	int blocks_used_for_bitmap = fsh.block_count / (FS_BLOCK_SIZE * 8);
	if (fsh.block_count % (FS_BLOCK_SIZE * 8))
		blocks_used_for_bitmap++;

	for (int i = 0; i < blocks_used_for_bitmap; i++) {
		unsigned char bitmap_block[FS_BLOCK_SIZE];
		read_block(i+1, (void *) bitmap_block);

		for (int j = 0; j < FS_BLOCK_SIZE; j++) {
			if (!(~(bitmap_block[j]))) {
				b += 8;
			} else {
				for (int k = 0; k < 8; k++, b++) {
					if (!((bitmap_block[j]) & (1 << k))) {
						return b;
					}
				}
			}
		}
	}

	return 0;
}

static unsigned int find_free_inode_ptr(void)
{
	unsigned int i = 1;  // inode0 always points to root dir, so can't be free

	struct fs_header fsh;
	read_block(0, (void *) &fsh);

	// search fs_header
	for ( ; i < BLOCK_ADDRESSES_PER_INODE; i++) {
		if (fsh.inode_ptrs[i] == 0) {
			if (i < fsh.max_inode_count) {
				return i;
			} else {
				return 0;
			}
		}
	}

	// search fs_header_extensions
	struct fs_header_extension ext;
	unsigned int next_extension = fsh.next_extension;

	while (next_extension) {
		read_block(next_extension, (void *) &ext);
		next_extension = ext.next_extension;

		for (int j = 0; j < BLOCK_ADDRESSES_PER_INODE_EXTENSION; j++, i++) {
			if (ext.inode_ptrs[j] == 0) {
				if (i < fsh.max_inode_count) {
					return i;
				} else {
					return 0;
				}
			}
		}
	}

	if (i < fsh.max_inode_count) {
		return i;
	} else {
		return 0;
	}
}

static unsigned int read_inode_ptr(unsigned int inode_ptr)
{
	if ((inode_ptr / BLOCK_ADDRESSES_PER_INODE) == 0) {
		// inode_ptr is in the fs_header
		struct fs_header fsh;
		int read_result = read_block(0, &fsh);
		if (FS_BLOCK_SIZE != read_result) {
			if (read_result < 0) {
				pr_err("failed to read fs header from device '%s'\n", used_file_path);
			} else {
				pr_err("failed to read full header from device (read %d/%d bytes)\n", read_result, FS_BLOCK_SIZE);
			}

			return 0;
		}

		return fsh.inode_ptrs[inode_ptr];
	} else {
		pr_err("inode_ptr %d is in fs_header_extension, reading is not implemented\n", inode_ptr);
		return 0;
		// TODO: find block with relevant inode_ptr
		/*
		unsigned int relevant_block_index = ((free_block_index - BLOCK_ADDRESSES_PER_INODE) / BLOCK_ADDRESSES_PER_INODE_EXTENSION) + 1;
		unsigned int relevant_block_record_offset = (free_block_index - BLOCK_ADDRESSES_PER_INODE) % BLOCK_ADDRESSES_PER_INODE_EXTENSION;
		*/
	}
}

static void write_inode_ptr(unsigned int inode_ptr, unsigned int block_ptr)
{
	if ((inode_ptr / BLOCK_ADDRESSES_PER_INODE) == 0) {
		// inode_ptr is in the fs_header
		struct fs_header fsh;
		int read_result = read_block(0, &fsh);
		if (FS_BLOCK_SIZE != read_result) {
			if (read_result < 0) {
				pr_err("failed to read fs header from device '%s'\n", used_file_path);
			} else {
				pr_err("failed to read full header from device (read %d/%d bytes)\n", read_result, FS_BLOCK_SIZE);
			}

			return;
		}

		fsh.inode_ptrs[inode_ptr] = block_ptr;

		int write_result = write_block(0, (void *) &fsh);
		if (FS_BLOCK_SIZE != write_result) {
			if (write_result < 0) {
				pr_err("failed to write fs header to device '%s'\n", used_file_path);
			} else {
				pr_err("failed to write full block to device, written %d/%d bytes\n", write_result, FS_BLOCK_SIZE);
			}

			return;
		}

		pr("Updated inode ptr %d -> %d\n", inode_ptr, block_ptr);
	} else {
		pr_err("inode_ptr %d is in fs_header_extension, writing is not implemented\n", inode_ptr);
		// TODO: find block with relevant inode_ptr, extend fs_header if needed
		/*
		unsigned int relevant_block_index = ((free_block_index - BLOCK_ADDRESSES_PER_INODE) / BLOCK_ADDRESSES_PER_INODE_EXTENSION) + 1;
		unsigned int relevant_block_record_offset = (free_block_index - BLOCK_ADDRESSES_PER_INODE) % BLOCK_ADDRESSES_PER_INODE_EXTENSION;
		*/
	}
}

char *fs_get_cwd(void)
{
	return fs_cwd;
}

int fs_chdir(void *d)
{
	memset(fs_cwd, 0, sizeof(fs_cwd));
	strcpy(fs_cwd, *((char**)d));

	return 0;
}

int fs_allow_write(void *d)
{
	if (used_file_fd <= 0) {
		pr_err("no device present\n");
		return 0;
	}

	pr_info("Allowing write operations on device '%s'\n", used_file_path);
	write_permitted = 1;

	return 0;
}

int fs_prohibit_write(void *d)
{
	if (used_file_fd <= 0) {
		pr_err("no device present\n");
		return 0;
	}

	pr_info("Prohibiting write operations on device '%s'\n", used_file_path);
	write_permitted = 0;

	return 0;
}

static int fs_find_free_directory_record(unsigned int dir_inode_ptr)
{
	struct fs_header fsh;
	read_block(0, (void *) &fsh);

	struct fs_inode dir;
	read_block(read_inode_ptr(dir_inode_ptr), (void *) &dir);

	int found_block_no = 0;

	// search in base inode
	for (unsigned int i = 0; i < BLOCK_ADDRESSES_PER_INODE; i++) {
		struct fs_directory_record r[DIRECTORY_RECORDS_PER_BLOCK];

		if (!dir.blocks[i]) {
			if (found_block_no < fsh.max_inode_count)
				return (found_block_no);
			else
				return -1;
		}

		read_block(dir.blocks[i], (void *) &r);

		for (int j = 0; j < DIRECTORY_RECORDS_PER_BLOCK; j++, found_block_no++) {
			if (r[j].inode_no)
				continue;

			if (found_block_no >= fsh.max_inode_count)
				return -1;

			return found_block_no;
		}
	}

	// search in inode extensions
	// TODO

	return -1;
}

static int *find_filename_in_directory(unsigned int dir_inode_ptr, char *fname)
{
	int dir_inode = read_inode_ptr(fs_cwd_inode_ptr);

	struct fs_inode dir;
	read_block(dir_inode, (void *) &dir);

	// list entries from base inode
	for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE; i++) {
		struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];

		if (dir.blocks[i]) {
			read_block(dir.blocks[i], (void *) &recs);

			for (int k = 0; k < DIRECTORY_RECORDS_PER_BLOCK; k++) {
				if (!recs[k].inode_no)
					continue;

				if (strcmp(fname, recs[k].fname))
					continue;

				// filename found
				int *r = malloc(sizeof(int) * 3);
				r[0] = i;
				r[1] = k;
				r[2] = recs[k].inode_no;
				return r;
			}
		}
	}

	return NULL;
}

static int fs_add_fname_to_directory(unsigned int dir_inode_ptr, unsigned int target_inode_ptr, char *fname)
{
	{
		// check if duplicate filename exists in specified directory
		int *r = find_filename_in_directory(dir_inode_ptr, fname);
		if (r) {
			free(r);
			pr_err("filename '%s' already exists\n", fname);
			return 0;
		}
	}

	int new_directory_record_index = fs_find_free_directory_record(dir_inode_ptr);
	if (new_directory_record_index < 0) {
		pr_err("no free inode pointer found\n");
		return -1;
	}

	if (new_directory_record_index < DIRECTORY_RECORDS_PER_BLOCK * BLOCK_ADDRESSES_PER_INODE) {
		// record is located in base inode, writing to it
		int block_no = new_directory_record_index / DIRECTORY_RECORDS_PER_BLOCK;
		int block_offset = new_directory_record_index % DIRECTORY_RECORDS_PER_BLOCK;

		struct fs_inode dir_inode;
		read_block(read_inode_ptr(dir_inode_ptr), (void *) &dir_inode);

		if (dir_inode.blocks[block_no] == 0) {
			// allocate new block
			unsigned int new_block = find_free_block();
			if (new_block == 0) {
				pr_err("failed to allocate block to extend directory (inode_ptr=%d)\n", dir_inode_ptr);
				return -1;
			} else {
				pr("Allocated new physical block %d for inode_ptr=%d (inode=%d, inner_block_no=%d)\n",
						new_block, dir_inode_ptr, read_inode_ptr(dir_inode_ptr), block_no);
			}

			char zero_data[FS_BLOCK_SIZE] = {};
			memset(zero_data, 0, FS_BLOCK_SIZE);
			write_block(new_block, &zero_data);

			mark_used(new_block);

			dir_inode.blocks[block_no] = new_block;
			if (dir_inode.size <= block_no * FS_BLOCK_SIZE) {
				pr("Updated directory size at inode_ptr=%d: %d -> %d\n",
						dir_inode_ptr, dir_inode.size, (block_no + 1) * FS_BLOCK_SIZE);
				dir_inode.size = (block_no + 1) * FS_BLOCK_SIZE;
				write_block(read_inode_ptr(dir_inode_ptr), (void *) &dir_inode);
			}
		}

		struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];
		read_block(dir_inode.blocks[block_no], (void *) &recs);

		strcpy(recs[block_offset].fname, fname);
		recs[block_offset].inode_no = target_inode_ptr;

		write_block(dir_inode.blocks[block_no], (void *) &recs);

		pr("Written new directory record #%d for file '%s' (-> inode_ptr=%d) in inode_ptr=%d\n",
				new_directory_record_index, fname, target_inode_ptr, dir_inode_ptr);

		return 0;
	} else {
		// record is located in inode extension
		// TODO
	}
}

static int fs_remove_fname_from_directory(unsigned int dir_inode_ptr, char *fname)
{
	// find directory record with this fname
	int dir_inode = read_inode_ptr(fs_cwd_inode_ptr);

	struct fs_inode dir;
	read_block(dir_inode, (void *) &dir);

	// list entries from base inode
	for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE; i++) {
		struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];

		if (!dir.blocks[i])
			continue;

		read_block(dir.blocks[i], (void *) &recs);

		for (int k = 0; k < DIRECTORY_RECORDS_PER_BLOCK; k++) {
			if (!recs[k].inode_no)
				continue;

			if (strcmp(fname, recs[k].fname))
				continue;

			pr("Directory record for '%s' found in block=%d, record=%d, removing\n", fname, i, k);

			unsigned int inode_ptr_cache = recs[k].inode_no;
			unsigned int inode_location_cache = read_inode_ptr(recs[k].inode_no);

			// decrement ref_count
			struct fs_inode f;
			read_block(read_inode_ptr(recs[k].inode_no), (void *) &f);
			f.ref_count--;
			write_block(read_inode_ptr(recs[k].inode_no), (void *) &f);

			// clear directory record inode_ptr
			recs[k].inode_no = 0;
			write_block(dir.blocks[i], (void *) &recs);

			// if it drops to zero, nullify inode_ptr pointing to this inode
			if (f.ref_count)
				goto fs_remove_fname_from_directory_finish;

			pr("ref_count=0, clearing inode_ptr\n");
			write_inode_ptr(inode_ptr_cache, 0);

			// if no fd reference this inode, clean it up altogether
			int i;
			for (i = 0; i < FS_MAX_OPEN_FD; i++)
				if (fs_file_descriptions[i].inode == inode_location_cache)
					break;

			if (i != FS_MAX_OPEN_FD) {
				pr("Inode %d is still referenced by fd %d, not removing it\n",
						inode_location_cache, i);
				goto fs_remove_fname_from_directory_finish;
			}

			pr("No open fd reference inode %d, cleaning up\n", inode_location_cache);

			// clear blocks referenced in base inode
			for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE; i++) {
				if (f.blocks[i])
					mark_free(f.blocks[i]);
			}
			mark_free(inode_location_cache);

			// clear blocks referenced in inode extensions
			struct fs_inode_extension ext;
			unsigned int next_extension = f.next_extension;

			while (next_extension) {
				mark_free(next_extension);
				read_block(next_extension, (void *) &ext);
				next_extension = ext.next_extension;

				for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE_EXTENSION; i++) {
					if (ext.blocks[i])
						mark_free(ext.blocks[i]);
				}
			}

			goto fs_remove_fname_from_directory_finish;
		}
	}

	// list entries from inode extension
	// TODO

	pr_err("no such file '%s'\n", fname);
	return -1;

fs_remove_fname_from_directory_finish:
	pr("Removed fname from directory record successfully\n");
	return 0;
}

int fs_open(void *d)
{
	char *fname = *((char **) d);

	// find file inode
	struct fs_file_description fd;
	{
		int *r = find_filename_in_directory(fs_cwd_inode_ptr, fname);
		if (!r) {
			pr_err("no such file: '%s'\n", fname);
			return 0;
		}

		fd.inode = read_inode_ptr(r[2]);
		free(r);
	}
	fd.rw_offset = 0;

	// find free file descriptor
	int free_fd;
	for (free_fd = 0; (free_fd < FS_MAX_OPEN_FD) && (fs_file_descriptions[free_fd].inode); free_fd++);
	if (free_fd == FS_MAX_OPEN_FD) {
		pr_err("no free file descriptor found\n");
		return 0;
	}

	memcpy(&(fs_file_descriptions[free_fd]), &fd, sizeof(struct fs_file_description));

	pr_stdout("%d\n", free_fd);

	return 0;
}

int fs_seek(void *d)
{
	int fd = ((int *) d)[0];
	int offset = ((int *) d)[1];

	if (!fs_file_descriptions[fd].inode) {
		pr_err("fd %d is not open\n", fd);
		return 0;
	}

	struct fs_inode f;
	read_block(fs_file_descriptions[fd].inode, (void *) &f);

	if (offset > f.size) {
		pr_err("offset is larger than file (%d > %d)\n", offset, f.size);
		return 0;
	}

	pr("Moving rw_offset of fd %d: %d -> %d\n",
			fd, fs_file_descriptions[fd].rw_offset, offset);
	fs_file_descriptions[fd].rw_offset = offset;

	return 0;
}

static void read_fd_block(unsigned int fd, unsigned int block_index, unsigned char *buf)
{
	struct fs_inode f;
	read_block(fs_file_descriptions[fd].inode, (void *) &f);

	if (block_index < BLOCK_ADDRESSES_PER_INODE) {
		if (f.blocks[block_index])
			read_block(f.blocks[block_index], (void *) buf);
		else
			memset(buf, 0, FS_BLOCK_SIZE);
	} else {
		int ext_no = (block_index - BLOCK_ADDRESSES_PER_INODE) / BLOCK_ADDRESSES_PER_INODE_EXTENSION;
		int ext_offset = (block_index - BLOCK_ADDRESSES_PER_INODE) % BLOCK_ADDRESSES_PER_INODE_EXTENSION;

		unsigned int target_extension_address;
		unsigned int i;

		// seek to target extension address
		for (
			target_extension_address = f.next_extension, i = 0;
			(i < ext_no) && target_extension_address;
			i++
		) {
			struct fs_inode_extension ext;
			read_block(target_extension_address, (void *) &ext);
			target_extension_address = ext.next_extension;
		}

		if (!target_extension_address) {
			memset(buf, 0, FS_BLOCK_SIZE);
		} else {
			struct fs_inode_extension ext;
			read_block(target_extension_address, (void *) &ext);

			if (!ext.blocks[ext_offset])
				memset(buf, 0, FS_BLOCK_SIZE);
			else
				read_block(ext.blocks[ext_offset], (void *) buf);
		}
	}
}

static int write_fd_block(unsigned int fd, unsigned int block_index, unsigned char *buf)
{
	struct fs_inode f;
	read_block(fs_file_descriptions[fd].inode, (void *) &f);

	if (block_index < BLOCK_ADDRESSES_PER_INODE) {
		if (!f.blocks[block_index]) {
			int new_block = find_free_block();
			if (!new_block) {
				pr_err("failed to write to fd=%d block=%d: can't allocate block for writing file data\n",
						fd, block_index);
				return -1;
			}
			mark_used(new_block);

			f.blocks[block_index] = new_block;
			write_block(fs_file_descriptions[fd].inode, (void *) &f);
		}

		write_block(f.blocks[block_index], (void *) buf);
	} else {
		int ext_no = (block_index - BLOCK_ADDRESSES_PER_INODE) / BLOCK_ADDRESSES_PER_INODE_EXTENSION;
		int ext_offset = (block_index - BLOCK_ADDRESSES_PER_INODE) % BLOCK_ADDRESSES_PER_INODE_EXTENSION;

		// treat switch from base inode to inode extension as special case
		if (!f.next_extension) {
			int new_block = find_free_block();
			if (!new_block) {
				pr_err("failed to write to fd=%d block=%d: can't allocate block for inode extension\n",
						fd, block_index);
				return -1;
			}
			mark_used(new_block);

			struct fs_inode_extension ext;
			memset(&ext, 0, sizeof(struct fs_inode_extension));

			f.next_extension = new_block;
			write_block(fs_file_descriptions[fd].inode, (void *) &f);
		}

		unsigned int target_extension_address;
		unsigned int previous_extension_address = f.next_extension;
		unsigned int i;

		// seek to target extension address
		for (
			target_extension_address = previous_extension_address, i = 0;
			(i < ext_no);
			i++
		) {
			if (!target_extension_address) {
				int new_block = find_free_block();
				if (!new_block) {
					pr_err("failed to write to fd=%d block=%d: can't allocate block for inode extension\n",
							fd, block_index);
					return -1;
				}
				mark_used(new_block);

				// updating previous inode extension
				struct fs_inode_extension prev_ext;
				read_block(previous_extension_address, (void *) &prev_ext);  // read
				prev_ext.next_extension = new_block;                         // modify
				write_block(previous_extension_address, (void *) &prev_ext); // write

				// writing new inode extension
				struct fs_inode_extension ext;
				memset(&ext, 0, sizeof(struct fs_inode_extension));
				write_block(target_extension_address, (void *) &ext);
			}

			struct fs_inode_extension ext;
			read_block(target_extension_address, (void *) &ext);
			previous_extension_address = target_extension_address;
			target_extension_address = ext.next_extension;
		}

		if (!target_extension_address) {
			int new_block = find_free_block();
			if (!new_block) {
				pr_err("failed to write to fd=%d block=%d: can't allocate block for inode extension\n",
						fd, block_index);
				return -1;
			}

			struct fs_inode_extension prev_ext;
			read_block(previous_extension_address, (void *) &prev_ext);  // read
			prev_ext.next_extension = new_block;                         // modify
			write_block(previous_extension_address, (void *) &prev_ext); // write

			int new_data_block = find_free_block();
			if (!new_data_block) {
				pr_err("failed to write to fd=%d block=%d: can't allocate block for data\n",
						fd, block_index);
				return -1;
			}

			mark_used(new_block);
			mark_used(new_data_block);

			// writing new inode extension
			struct fs_inode_extension ext;
			memset(&ext, 0, sizeof(struct fs_inode_extension));
			ext.blocks[ext_offset] = new_data_block;
			write_block(target_extension_address, (void *) &ext);

			// writing new data block
			write_block(new_data_block, (void *) buf);
		} else {
			struct fs_inode_extension ext;
			read_block(target_extension_address, (void *) &ext);

			if (!ext.blocks[ext_offset]) {
				int new_data_block = find_free_block();
				if (!new_data_block) {
					pr_err("failed to write to fd=%d block=%d: can't allocate block for data\n",
							fd, block_index);
					return -1;
				}
				mark_used(new_data_block);

				ext.blocks[ext_offset] = new_data_block;
				write_block(target_extension_address, (void *) &ext);
			}

			write_block(ext.blocks[ext_offset], (void *) buf);
		}
	}
}

int fs_read(void *d)
{
	int fd = ((int *) d)[0];
	int amount = ((int *) d)[1];

	if (!fs_file_descriptions[fd].inode) {
		pr_err("fd %d is not open\n", fd);
		return 0;
	}

	if (amount <= 0)
		return 0;

	struct fs_inode f;
	read_block(fs_file_descriptions[fd].inode, (void *) &f);

	if (fs_file_descriptions[fd].rw_offset + amount > f.size) {
		pr_err("can not read outside of a file (offset %d + amount %d > f.size %d)\n",
				fs_file_descriptions[fd].rw_offset, amount, f.size);
		return 0;
	}

	pr("Reading %d bytes from fd %d (offset %d)\n",
			amount, fd, fs_file_descriptions[fd].rw_offset);

	unsigned char *read_data = malloc(amount);
	unsigned int total_read_data_amount = 0;

	// read from first block
	unsigned char block_buffer[FS_BLOCK_SIZE];

	int block_index = fs_file_descriptions[fd].rw_offset / FS_BLOCK_SIZE;
	int block_offset = fs_file_descriptions[fd].rw_offset % FS_BLOCK_SIZE;

	read_fd_block(fd, block_index, block_buffer);

	if (block_offset + amount <= FS_BLOCK_SIZE) {
		memcpy(read_data, &(block_buffer[block_offset]), amount);
		goto print_read_data;
	} else {
		memcpy(read_data, &(block_buffer[block_offset]), FS_BLOCK_SIZE - block_offset);
		total_read_data_amount += FS_BLOCK_SIZE - block_offset;
	}

	// read from all next blocks
	while (amount - total_read_data_amount > 0) {
		block_index++;
		read_fd_block(fd, block_index, block_buffer);
		int bytes_to_read = (amount - total_read_data_amount > FS_BLOCK_SIZE)
			? FS_BLOCK_SIZE : amount - total_read_data_amount;

		memcpy(&(read_data[total_read_data_amount]), block_buffer, bytes_to_read);
		total_read_data_amount += bytes_to_read;
	}

print_read_data:
	pr("Updating fd %d offset: %d -> %d\n",
			fd, fs_file_descriptions[fd].rw_offset, fs_file_descriptions[fd].rw_offset+amount);
	fs_file_descriptions[fd].rw_offset += amount;

	write_stdout(read_data, amount);
	pr_stdout("\n");

	free(read_data);

	return 0;
}

int fs_write(void *d)
{
	int fd = ((int *) d)[0];
	char *str = *((char **) d+4);
	int str_len = strlen(str);

	if (!fs_file_descriptions[fd].inode) {
		pr_err("fd %d is not open\n", fd);
		return 0;
	}

	if (str_len == 0)
		return 0;

	int block_index = fs_file_descriptions[fd].rw_offset / FS_BLOCK_SIZE;
	int block_offset = fs_file_descriptions[fd].rw_offset % FS_BLOCK_SIZE;

	unsigned char data_buffer[FS_BLOCK_SIZE];

	if (block_offset + str_len <= FS_BLOCK_SIZE) {
		read_fd_block(fd, block_index, data_buffer);
		memcpy(&(data_buffer[block_offset]), str, str_len);
		write_fd_block(fd, block_index, data_buffer);
	} else {
		read_fd_block(fd, block_index, data_buffer);
		memcpy(&(data_buffer[block_offset]), str, FS_BLOCK_SIZE - block_offset);
		write_fd_block(fd, block_index, data_buffer);

		read_fd_block(fd, block_index+1, data_buffer);
		memcpy(data_buffer, &(str[FS_BLOCK_SIZE - block_offset]), str_len - block_offset);
		write_fd_block(fd, block_index+1, data_buffer);
	}

	pr("Moving fd %d offset: %d -> %d\n",
			fd, fs_file_descriptions[fd].rw_offset, fs_file_descriptions[fd].rw_offset + str_len);
	fs_file_descriptions[fd].rw_offset += str_len;

	return 0;
}

int fs_close(void *d)
{
	int fd = *((int *) d);

	// remove inode number from fd
	if (!fs_file_descriptions[fd].inode) {
		pr_err("fd %d is not open\n", fd);
		return 0;
	}

	unsigned int inode_location_cache = fs_file_descriptions[fd].inode;

	fs_file_descriptions[fd].inode = 0;
	pr("fd %d closed\n", fd);

	// cleanup file data on disk if ref_count=0
	// and no other open descriptor references it's inode

	struct fs_inode f;
	read_block(inode_location_cache, (void *) &f);
	if (f.ref_count)
		return 0;

	for (int i = 0; i < FS_MAX_OPEN_FD; i++)
		if (fs_file_descriptions[i].inode == inode_location_cache)
			return 0;

	// if ended up here, the inode is not referenced anywhere
	pr("No open fd reference inode %d, cleaning up\n", inode_location_cache);

	// clear blocks referenced in base inode
	for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE; i++) {
		if (f.blocks[i])
			mark_free(f.blocks[i]);
	}
	mark_free(inode_location_cache);

	// clear blocks referenced in inode extensions
	struct fs_inode_extension ext;
	unsigned int next_extension = f.next_extension;

	while (next_extension) {
		mark_free(next_extension);
		read_block(next_extension, (void *) &ext);
		next_extension = ext.next_extension;

		for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE_EXTENSION; i++) {
			if (ext.blocks[i])
				mark_free(ext.blocks[i]);
		}
	}
}


int fs_create(void *d)
{
	if (!write_permitted) {
		pr_err("write operations are prohibited\n");
		return 0;
	}

	char *fname = *((char **) d);
	int fname_len = strlen(fname);

	{
		// check if duplicate filename exists in current directory
		int *r = find_filename_in_directory(fs_cwd_inode_ptr, fname);
		if (r) {
			free(r);
			pr_err("filename '%s' already exists\n", fname);
			return 0;
		}
	}

	if (fname_len > 59) {
		pr_err("filename too long (%d > %d)\n", fname_len, 59);
		return 0;
	}

	pr("Creating regular file '%s'\n", fname);

	int inode_block_no = find_free_block();
	if (!inode_block_no) {
		pr_err("no free blocks available to save file inode\n");
		return 0;
	}

	// write new file inode
	struct fs_inode newf = {};
	newf.ftype = REGULAR;
	newf.ref_count = 1;
	newf.size = 0;

	{
		int bytes_written = write_block(inode_block_no, (void *) &newf);

		if (bytes_written < 0) {
			pr_err("failed to write inode block to device '%s'\n", used_file_path);
			return 0;
		} else if (bytes_written < FS_BLOCK_SIZE) {
			pr_err("failed to write full inode block to device '%s' (written %d/%d bytes)\n",
					used_file_path, bytes_written, FS_BLOCK_SIZE);
			return 0;
		} else {
			pr("Written inode block to device '%s'\n", used_file_path);
		}

		mark_used(inode_block_no);
	}

	// allocate and write inode pointer for new inode
	unsigned int inode_ptr_index = find_free_inode_ptr();
	if (!inode_ptr_index) {
		pr_err("no free inode ptr found\n");
		return 0;
	}
	write_inode_ptr(inode_ptr_index, inode_block_no);

	// add filename to current directory inode
	fs_add_fname_to_directory(fs_cwd_inode_ptr, inode_ptr_index, fname);

	return 0;
}

int fs_ln(void *d)
{
	if (used_file_fd <= 0) {
		pr_err("no storage device\n");
		return 0;
	}

	char *existing_fname = ((char **) d)[0];
	char *new_fname = ((char **)d)[1];
	int new_fname_len = strlen(new_fname);

	{
		// check if duplicate filename exists in current directory
		int *r = find_filename_in_directory(fs_cwd_inode_ptr, new_fname);
		if (r) {
			free(r);
			pr_err("filename '%s' already exists\n", new_fname);
			return 0;
		}
	}


	if (new_fname_len > 59) {
		pr_err("new filename too long (%d > 59)\n", new_fname_len);
		return 0;
	}

	pr("Making hard link '%s' -> '%s'\n", new_fname, existing_fname);

	// find original file name
	unsigned int original_inode_ptr = 0;

	int dir_inode = read_inode_ptr(fs_cwd_inode_ptr);

	struct fs_inode dir;
	read_block(dir_inode, (void *) &dir);

	// list entries from base inode
	for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE; i++) {
		struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];

		if (dir.blocks[i]) {
			read_block(dir.blocks[i], (void *) &recs);

			for (int k = 0; k < DIRECTORY_RECORDS_PER_BLOCK; k++) {
				if (!recs[k].inode_no)
					continue;

				if (!strcmp(existing_fname, recs[k].fname)) {
					original_inode_ptr = recs[k].inode_no;
					goto original_inode_ptr_found;
				}
			}
		}
	}

	// list entries from inode extensions
	// TODO

	pr_err("no such file '%s'\n", existing_fname);
	return 0;

original_inode_ptr_found:
	pr("Original inode_ptr found (%d)\n", original_inode_ptr);

	// register new filename with the same inode_ptr
	if (fs_add_fname_to_directory(fs_cwd_inode_ptr, original_inode_ptr, new_fname) < 0) {
		pr_err("failed to register filename in directory '%s'\n", fs_cwd);
		return 0;
	} else {
		pr("Registered new filename in directory '%s'\n", fs_cwd);
	}

	// update ref_count in file inode
	struct fs_inode f;
	read_block(read_inode_ptr(original_inode_ptr), (void *) &f);
	f.ref_count++;
	write_block(read_inode_ptr(original_inode_ptr), (void *) &f);

	pr("Updated inode ref_count (%d -> %d)\n", f.ref_count-1, f.ref_count);
}

int fs_rm(void *d)
{
	if (!write_permitted) {
		pr_err("device '%s' is write-protected\n", used_file_path);
		return 0;
	}

	char *fname = *((char **) d);

	if (fs_remove_fname_from_directory(fs_cwd_inode_ptr, fname) < 0) {
		pr_err("failed to unlink '%s'\n", fname);
	} else {
		pr("Unlinked '%s'\n", fname);
	}

	return 0;
}

int fs_ls(void *d)
{
	if (used_file_fd <= 0) {
		pr_err("no storage device\n");
		return 0;
	}

	int dir_inode = read_inode_ptr(fs_cwd_inode_ptr);

	struct fs_inode dir;
	read_block(dir_inode, (void *) &dir);

	// list entries from base inode
	for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE; i++) {
		struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];

		if (dir.blocks[i]) {
			read_block(dir.blocks[i], (void *) &recs);

			for (int k = 0; k < DIRECTORY_RECORDS_PER_BLOCK; k++) {
				if (!recs[k].inode_no)
					continue;

				pr_stdout("%s\n", recs[k].fname);
			}
		}
	}

	// list entries from inode extension
	// TODO

	return 0;
}

int fs_la(void *d)
{
	if (used_file_fd <= 0) {
		pr_err("no storage device\n");
		return 0;
	}

	int dir_inode = read_inode_ptr(fs_cwd_inode_ptr);

	struct fs_inode dir;
	read_block(dir_inode, (void *) &dir);

	pr_stdout("directory size: %d\n", dir.size);

	// list entries from base inode
	for (int i = 0; i < BLOCK_ADDRESSES_PER_INODE; i++) {
		struct fs_directory_record recs[DIRECTORY_RECORDS_PER_BLOCK];

		if (dir.blocks[i]) {
			read_block(dir.blocks[i], (void *) &recs);

			for (int k = 0; k < DIRECTORY_RECORDS_PER_BLOCK; k++) {
				if (!recs[k].inode_no)
					continue;

				struct fs_inode f_inode;
				read_block(read_inode_ptr(recs[k].inode_no), (void *) &f_inode);

				if (f_inode.ftype == DIRECTORY) {
					pr_stdout(COLOR_BLUE "%s" COLOR_RESET
							"(inode_ptr=%d -> inode=%d, ref_count=%d, size=%d, type=dir)\n",
							recs[k].fname, recs[k].inode_no, read_inode_ptr(recs[k].inode_no),
							f_inode.ref_count, f_inode.size);
				} else {
					pr_stdout("%s (inode_ptr=%d -> inode=%d, ref_count=%d, size=%d, type=reg)\n",
							recs[k].fname, recs[k].inode_no, read_inode_ptr(recs[k].inode_no),
							f_inode.ref_count, f_inode.size);
				}
			}
		}
	}

	// list entries from inode extension
	// TODO

	return 0;
}

int fs_use(void *d)
{
	char *fname = *((char **) d);
	int name_len = strlen(fname);

	if (name_len > FS_MAX_DEVICE_FILE_NAME_LEN) {
		pr_err("device filename too long (> %d)\n", FS_MAX_DEVICE_FILE_NAME_LEN);
		return 0;
	}

	pr("Using file '%s' as storage device\n", fname);

	strcpy(used_file_path, fname);

	if (used_file_fd > 0)
		close(used_file_fd);

	used_file_fd = open(fname, O_RDWR);

	if (used_file_fd < 0) {
		pr_err("failed to open filename '%s'\n", fname);
		return 0;
	}

	int fs_version = identify_fs();
	if (!fs_version) {
		pr_info("filesystem could not be identified on device '%s'\n", fname);
		write_permitted = 0;
	} else if (fs_version != 1) {
		pr_warn("filesystem is corrupted or has unsupported version (0x%hhx)\n", fs_version);
		write_permitted = 0;
	} else if (fs_version == 1) {
		pr_info("filesystem v1 has been identified on device '%s'\n", fname);
		write_permitted = 1;
	}

	if (write_permitted) {
		char *root_dir_path = "/";
		fs_chdir((void *) &root_dir_path);

		fs_cwd_inode_ptr = 0;
	}

	return 0;
}

int fs_mkfs(void *d)
{
	if (!write_permitted) {
		pr_err("device '%s' is write-protected\n", used_file_path);
		return 0;
	}

	if (used_file_fd <= 0) {
		pr_err("storage device not present\n");
		return 0;
	}

	int max_inode_count = *((int *)d);

	if (max_inode_count <= 0) {
		pr_err("max inode count must be positive (got %d)\n", max_inode_count);
		return 0;
	}

	struct stat st;
	if (fstat(used_file_fd, &st) < 0) {
		pr_err("could not stat device '%s'\n", used_file_path);
		return 0;
	}

	int block_count = st.st_size / FS_BLOCK_SIZE;
	int blocks_used_for_bitmap = block_count / (FS_BLOCK_SIZE * 8);
	if (block_count % (FS_BLOCK_SIZE * 8))
		blocks_used_for_bitmap++;

	if (blocks_used_for_bitmap > FS_MAX_BITMAP_SIZE) {
		pr_err("memory bitmap is too large (%d blocks > %d)\n", blocks_used_for_bitmap, FS_MAX_BITMAP_SIZE);
		return 0;
	}

	pr("Formatting storage device '%s' of size %d (total_block_count = %d, bitmap_blocks = %d) with %d allowed inode pointers\n", used_file_path, st.st_size, block_count, blocks_used_for_bitmap, max_inode_count);

	struct fs_header fsh = {};
	fsh.version = 0x1;
	fsh.max_inode_count = max_inode_count;
	fsh.block_count = block_count;

	pr("header size is %d bytes, writing it to the first block\n", sizeof(fsh));

	int result = write_block(0, (void *) &fsh);
	if (FS_BLOCK_SIZE != result) {
		if (result < 0) {
			pr_err("failed to write fs header to device '%s'\n", used_file_path);
		} else {
			pr_err("failed to write full block to device, written %d/%d bytes\n", result, FS_BLOCK_SIZE);
		}

		return 0;
	}

	int blocks_used = 1 + blocks_used_for_bitmap;

	unsigned char bitmap_block[FS_BLOCK_SIZE];
	unsigned int j = 0;

	for (int i = 0; i < blocks_used_for_bitmap; i++) {
		memset(bitmap_block, 0, FS_BLOCK_SIZE);
		for (int k = 0; k < FS_BLOCK_SIZE; k++) {
			for (int t = 0; t < 8; t++, j++) {
				if (j == blocks_used)
					goto finish_current_block;

				bitmap_block[i] |= (1 << t);
			}
		}

finish_current_block:
		{
			int bytes_written = write_block(i+1, (void *) bitmap_block);

			if (bytes_written < 0) {
				pr_err("failed to write bitmap block %d/%d on device '%s'\n",
						i+1, blocks_used_for_bitmap, used_file_path);
				return 0;
			} else if (bytes_written < FS_BLOCK_SIZE) {
				pr_err("failed to write full bitmap block %d/%d on device '%s' (written %d/%d bytes)\n",
						i+1, blocks_used_for_bitmap, used_file_path, bytes_written, FS_BLOCK_SIZE);
				return 0;
			} else {
				pr("Written bitmap block %d/%d on device '%s'\n", i+1, blocks_used_for_bitmap, used_file_path);
			}
		}
	}


	// create root directory automatically

	struct fs_inode root_dir = {};
	root_dir.ftype = DIRECTORY;
	root_dir.ref_count = 1;

	unsigned int free_block_index = find_free_block();

	if (!free_block_index) {
		pr_err("failed to find free block for root directory\n");
		return 0;
	}

	{
		int bytes_written = write_block(free_block_index, (void *) &root_dir);
		if (bytes_written < 0) {
			pr_err("failed to write root directory block on device '%s'\n", used_file_path);
			return 0;
		} else if (bytes_written < FS_BLOCK_SIZE) {
			pr_err("failed to write full root directory block on device '%s' (written %d/%d bytes)\n",
					used_file_path, bytes_written, FS_BLOCK_SIZE);
			return 0;
		} else {
			pr("Written root directory block on device '%s'\n", used_file_path);
		}
	}
	mark_used(free_block_index);

	// inode0 -> root_dir_block
	write_inode_ptr(0, free_block_index);

	char *root_dir_path = "/";
	fs_chdir((void *) &root_dir_path);

	fs_cwd_inode_ptr = 0;

	return 0;
}