/*
* Read from an opend file.
* Read can not enlarge file. So you should not read outside the size of
* the file. If the read exceeds the file size, its result will be truncated.
*
* This function returns the number of bytes read.
*/
int sfs_read(int fd, void *buf, int length)
{
int remaining, to_copy, offset;
blkid *bids;
int i, n;
char *p = (char *)buf;
char tmp[BLOCK_SIZE];
u32 cur = fdtable[fd].cur;
/* TODO: check if we need to truncate */
if ((cur + length) > fdtable[fd].inode.size)
{
// Need to truncate, remove the last portion
length = fdtable[fd].inode.size - length;
}
/* TODO: similar to the sfs_write() */
// Get the block ids of content
bids = malloc(length/BLOCK_SIZE + 1);
n = sfs_get_file_content(bids, fd, cur, length);
// Read operation
remaining = length;
offset = cur % BLOCK_SIZE;
if (BLOCK_SIZE - offset > remaining)
{
to_copy = remaining;
}
else
{
to_copy = BLOCK_SIZE - offset;
}
for (i = 0; i < n; i++)
{
sfs_read_block((char*)&tmp, bids[i]);
memcpy(buf, tmp+offset, to_copy);
remaining -= to_copy;
offset = 0;
if (remaining > BLOCK_SIZE)
{
to_copy = BLOCK_SIZE - offset;
} else {
to_copy = remaining;
}
}
// Update variables
fdtable[fd].cur += length;
free(bids);
return length;
}
/*
* Read from an opened file.
* Read can not enlarge file. So you should not read outside the size of
* the file. If the read exceeds the file size, its result will be truncated.
*
* This function returns the number of bytes read.
*/
int sfs_read(int fd, void *buf, int length)
{
int remaining, to_copy, offset;
int frame_start, frame_end, content_blk, num_blocks;
int i, n;
char *p = (char *)buf;
char inode_ptr[BLOCK_SIZE];
char tmp[BLOCK_SIZE];
u32 cur = fdtable[fd].cur;
sfs_inode_t inode;
sfs_read_block(inode_ptr, fdtable[fd].inode_bid);
inode = *(sfs_inode_t*)inode_ptr;
remaining = length;
num_blocks = (length / BLOCK_SIZE) + 1;
blkid bids[num_blocks];
//Find frame holding the cursor
frame_start = cur / (SFS_FRAME_COUNT * BLOCK_SIZE);
//Find the frame that would be holding the last byte we want to read
frame_end = (cur + length) / (SFS_FRAME_COUNT * BLOCK_SIZE);
int num_frames = frame_start - frame_end + 1;
content_blk = cur / BLOCK_SIZE;
offset = cur % BLOCK_SIZE;
//Traverse the frames and check if the length exceeds the
//number of frames
blkid frame_bid = inode.first_frame;
sfs_inode_frame_t frame;
int count = 0;
int nonzero_block = 0;
//Truncate file to the smallest BLOCK
//The first and last blocks will have fewer bytes stored
//Check frames to determine if all content blocks exist
while(count < num_blocks){
//Read the next frame
sfs_read_block(tmp, frame_bid);
frame = *(sfs_inode_frame_t*)tmp;
frame_bid = frame.next;
//Count the number of nonzero indices in the content array
while(content_blk < SFS_FRAME_COUNT && count < num_blocks){
if(frame.content[content_blk] != 0){
nonzero_block++;
count++;
content_blk++;
}
}
//Reset index to zero
content_blk = 0;
if(frame_bid == 0 && count < num_frames){
printf("The specified length exceeds the file size.\n");
break;
}
}
//The length exceeds the number of valid blocks, truncate read
if(count < num_blocks){
//Add fewer bytes from first block
remaining = BLOCK_SIZE - offset;
num_blocks--;
//Add the remaining blocks
remaining = remaining + num_blocks * BLOCK_SIZE;
} else{
remaining = length;
}
/* TODO: similar to the sfs_write() */
int num_content_blocks = sfs_get_file_content(bids, fd, cur, length);
int bid_count = 0;
char block_ptr[BLOCK_SIZE];
while(remaining > 0){
to_copy = 0;
sfs_read_block(block_ptr, bids[bid_count]);
//Case 1: Read block with offset
if(offset != 0){
//Partially fill block
if(remaining < (BLOCK_SIZE - offset)){
to_copy = remaining;
} else{
//Fill entire block
to_copy = BLOCK_SIZE - offset;
}
strncpy(buf, block_ptr+offset, to_copy);
offset = 0;
} else if(remaining > BLOCK_SIZE){
//Case 2: Write to a full block
to_copy = BLOCK_SIZE;
strncpy(buf, block_ptr, to_copy);
} else{
//Case 3: Write a partial block
to_copy = remaining;
strncpy(buf, block_ptr, to_copy);
}
remaining = remaining - to_copy;
cur = cur + to_copy;
fdtable[fd].cur = cur;
bid_count++;
}
return length - remaining;
}
/*
* Write to a file. This function can potentially enlarge the file if the
* cur+length exceeds the size of file. Also you should be aware that the
* cur may already be larger than the size (due to sfs_seek). In such
* case, you will need to expand the file as well.
*
* This function returns number of bytes written.
*/
int sfs_write(int fd, void *buf, int length)
{
int remaining, offset, to_copy;
char *p = (char *)buf;
char tmp[BLOCK_SIZE];
char inode_ptr[BLOCK_SIZE];
u32 cur = fdtable[fd].cur;
u32 buf_offset = 0;
sfs_inode_t inode;
remaining = length;
offset = cur % BLOCK_SIZE;
int numBids = (length / BLOCK_SIZE) + 1;
blkid bids[numBids];
sfs_read_block(inode_ptr, fdtable[fd].inode_bid);
inode = *(sfs_inode_t*)inode_ptr;
blkid frame_bid = inode.first_frame;
/* TODO: check if we need to resize */
sfs_inode_frame_t frame;
sfs_read_block(tmp, frame_bid);
frame = *(sfs_inode_frame_t*)tmp;
if( (length + cur) > inode.size){
u32 new_size = length + cur;
fdtable[fd].inode = inode;
sfs_resize_file(fd, new_size);
}
/* TODO: get the block ids of all contents (using sfs_get_file_content() */
int num_blocks = sfs_get_file_content(bids, fd, cur, length);
/* TODO: main loop, go through every block, copy the necessary parts
to the buffer, consult the hint in the document. Do not forget to
flush to the disk.
*/
char block_ptr[BLOCK_SIZE];
int bid_count = 0;
//The block numbers should already be known by this part
while(remaining > 0){
to_copy = 0;
sfs_read_block(block_ptr, bids[bid_count]);
//Case 1: Write to block with offset
if(offset != 0){
//Partially fill block
if(remaining < (BLOCK_SIZE - offset)){
to_copy = remaining;
} else{
//Fill entire block
to_copy = BLOCK_SIZE - offset;
}
strncpy(block_ptr+offset, buf, to_copy);
offset = 0;
} else if(remaining > BLOCK_SIZE){
//Case 2: Write to a full block
to_copy = BLOCK_SIZE;
strncpy(block_ptr, buf, to_copy);
} else{
//Case 3: Write a partial block
to_copy = remaining;
strncpy(block_ptr, buf, to_copy);
}
sfs_write_block(&block_ptr, bids[bid_count]);
remaining = remaining - to_copy;
cur = cur + to_copy;
bid_count++;
}
fdtable[fd].cur = cur;
return length - remaining;
}
/*
* Write to a file. This function can potentially enlarge the file if the
* cur+length exceeds the size of file. Also you should be aware that the
* cur may already be larger than the size (due to sfs_seek). In such
* case, you will need to expand the file as well.
*
* This function returns number of bytes written.
*/
int sfs_write(int fd, void *buf, int length)
{
int remaining, offset, to_copy;
blkid *bids;
int i, n;
char *p = (char *)buf;
char tmp[BLOCK_SIZE];
u32 cur = fdtable[fd].cur;
int frame_size, new_nframe, old_nframe;
/* TODO: check if we need to resize */
frame_size = BLOCK_SIZE * SFS_FRAME_COUNT;
old_nframe = (fdtable[fd].inode.size + frame_size-1)/frame_size;
new_nframe = ((cur+length) + frame_size-1)/frame_size;
if (new_nframe > old_nframe)
{
// Need to allocate a new frame
sfs_resize_file(fd, fdtable[fd].inode.size + length);
}
/* TODO: get the block ids of all contents (using sfs_get_file_content() */
bids = malloc(length/BLOCK_SIZE + 1);
n = sfs_get_file_content(bids, fd, cur, length);
/* TODO: main loop, go through every block, copy the necessary parts
to the buffer, consult the hint in the document. Do not forget to
flush to the disk.
*/
remaining = length;
offset = cur % BLOCK_SIZE;
if (BLOCK_SIZE - offset > remaining)
{
to_copy = remaining;
}
else
{
to_copy = BLOCK_SIZE - offset;
}
for (i = 0; i < n; i++)
{
memcpy(tmp + offset , buf, to_copy);
sfs_write_block((char*)&tmp, bids[i]);
remaining -= to_copy;
offset = 0;
if (remaining > BLOCK_SIZE)
{
to_copy = BLOCK_SIZE - offset;
}
else
{
to_copy = remaining;
}
}
/* TODO: update the cursor and free the temp buffer
for sfs_get_file_content()
*/
fdtable[fd].cur += length;
if (fdtable[fd].inode.size < fdtable[fd].cur)
{
fdtable[fd].inode.size = fdtable[fd].cur;
}
sfs_write_block((char*)&(fdtable[fd].inode), fdtable[fd].inode_bid);
free(bids);
return length;
}