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CMPSC 311 - Introduction
to Systems Programming
Assignment #2 – The Lion Cloud Driver v1.0
Professor Patrick McDaniel
CMPSC 311 - Introduction to Systems Programming
Overview
• Idea you are to maintain the correct file
contents in a Cloud Based virtual storage
device.
• You will write code to communicate with a
devices over a a virtualized bus that will
store file-system data.
• 3 things to know
‣ How file I/O works
‣ How the LoinCloud bus works
‣ How to make the memory device stuff look
like files
LC Simulator (provided)
LC Filesystem Driver (your code)
LC
LC Storage Device
(device I/O bus)
Assignment Basics
• You are to write the file operation functions defined in the lcloud_filesys.c
‣ Translate then file operations into device IO operations
‣ Maintain, in the memory device, the file contents
• You must insert data, read data, and maintain a file handle and a file
allocation data.
• Your code: open, read, write, close, seek …
• Your code will be exercised by the simulator given to you (it will call your
functions and verify the data you are returning is correct).
Your driver
• LcFHandle lcopen( const char *path ); - This function will open a file
(named path, e.g.,) in the filesystem. If the file does not exist, it should be created and set
to zero length. If it does exist, it should be opened and its read/write postion should be
set to the first byte. Note that there are no subdirectories in the filesystem, just files (so
you can treat the path as a filename). The function should return a unique file handle
used for subsequent operations or -1 if a failure occurs.
• int lcclose( LcFHandle fh ); - This function closes the file referenced by the
file handle that was previously open. The function should fail (and return -1) if the file
handle is bad or the file was not previously open.
• int lcread( LcFHandle fh, char *buf, size_t len ); - This function
should read count bytes from the file referenced by the file handle at the current position.
Note that if there are not enough bytes left in the file, the function should read to the end
of the file and return the number of bytes read. If there are enough bytes to fulfill the
read, the function should return count. The function should fail (and return -1) if the file
handle is bad or the file was not previously open.
Your driver (cont.)
• int lcwrite( LcFHandle fh, char *buf, size_t len ); - The function
should write count bytes into the file referenced by the file handle. If the write goes
beyond the end of the file the size should be increased. The function should always return
the number of bytes written, e.g., count. The function should fail (and return -1) if the file
handle is bad or the file was not previously open.
• int lcseek( LcFHandle fh, size_t off ); - The function should set the
current position into the file to loc, where 0 is the first byte in the file. The function should
fail (and return -1) if the loc is beyond the end of the file, the file handle is bad or the file
was not previously open.
• int lcshutdown( void ); - - The function should shut down the system, including
powering off the devices and closing all files.
Maintaining file contents
len=0, pos=0
open(“file.txt”)
X X X X X
len=5, pos=5
write(“XXXXX”, 5)
X X X X X
len=5, pos=2
seek(2)
X X X X X
len=5, pos=5
read(4)
• Open prepares an empty file for reading (zero length)
• Write writes bytes into the file
• Seek seeks to a position in the file (end if pos > length)
• Read copies up to length number of bytes from the file
• Close deletes the contents
Lion Cloud Devices
• Each device has LC_DEVICE_NUMBER_SECTORS sectors and
LC_DEVICE_NUMBER_BLOCKS blocks. The blocks and sectors are zero indexed.
• A frame is memory block of LC_DEVICE_BLOCK_SIZE bytes.
• You can assume that there is only one device in the system.
LC
Sector 0
Block 0
Block 1
Block 2
Block b-1

Sector 1
Block 0
Block 1
Block 2
Block b-1

Sector s-1
Block 0
Block 1
Block 2
Block b-1


CART Opcode Execution
You communicate with devices through a set of registers
of different sizes that encode the opcode and arguments
for the operation. The “data” associated with the opcode
(where needed) is communicated through the fixed sized
transfer buffer (LC_DEVICE_BLOCK_SIZE).
LCloudRegisterFrame lcloud_io_bus( LCloudRegisterFrame frm, void *xfer );
B0 C0 C1 C2 D0 D1
4-bits 8-bits 8-bits 8-bits 16-bits 16-bits
B1
Most significant bit Least significant bit
Using the Lion Cloud Registers
• There are 7 registers: B0/B1 (4 bits), C0/C1/C2 (8 bits),
and D0/D1 (16 bits)
‣ B0 is always used to indicate who is the sender of the
message. It is always 0 when you are sending, 1 when it
is the devices responding.
‣ B1 always contains a return/status code, should always
be 0 when sending to devices. 1 is acknowledge/success
from device, anything else is failure.
‣ C0 is always the operation code (see LcOperationCode
type in lcloud_controller.h)
‣ The rest of the registers are dependent on the type of
operation being performed (see next)
B0 C0 C1 C2 D0 D1
4-bits 8-bits 8-bits 8-bits 16-bits 16-bits
B1
Most significant bit Least significant bit
Operation types / the IO bus
• LC_POWER_ON - Initialize interface to a given device
‣ All other registers should be 0 on both send and receive
• LC_POWER_OFF - Power off the device
‣ All other registers should be 0 on both send and receive
• LC_DEVPROBE - Probe the bus to see what devices are present
‣ d0 - contains a bit mask of present devices, where device there are a possible
16 devices, where the bit 2^x=1 indicates that device ID x is present. For
example if the 2^4 (16) is present, then you know device with ID 4 is on the bus.
Operation types / the IO bus (cont.)
• LC_BLOCK_XFER - Transfer a block to the device
‣ c1 - the device ID for the device to read from
‣ c2 - LC_XFER_WRITE for write, LC_XFER_READ for read
‣ d0 - sector to read/write from
‣ d1 - block to read/write from
LCloudRegisterFrame lcloud_io_bus( LCloudRegisterFrame frm, void *xfer );
xfer is NULL for every command except LC_BLOCK_XFER, in
which you put a pointer to a buffer to read or write from.
Summary
• To summarize, your code will receive commands from
the virtual application (simulator). It will do the
following functions to implement the device driver:
a. Power on the devices using the power on
b. Probe the bus to see what devices are available (one)
c. On writes, you have to figure out where to place the
data (and remember it)
d. On reads, return the previously stored data in those
blocks
e. Power off the controller when asked to
Start
POWER ON
PROBE BUS
OPEN
READ/WRITE
CLOSE
Honors option
• Honors option: When you receive the indication to shut down the device
cluster, you must go back and erase all of the data you wrote to the array.
That is you must write all zeros you previously used in any write operation,
regardless of what file it may have been mapped to. The program on exit will
indicate via the log whether you have successfully completed the honors
option:
Testing your program
• The testing of the program is performed by using the simulated
workloads. The main function provided to you simply calls the
simulator. To test the program, you execute the simulator using
the -v option, as:
• If you have implemented everything correctly, the log should
display the following message:
./lcloud_sim -v cmpsc311-assign2-manifest.txt cmpsc311-assign2-workload.txt
LionCloud simulation completed successfully!!!
Getting started …
• Get the file from the canvas page.
• Change into your development directory and unpack the file:
% cd ~/cmpsc311
% cp assign2-starter.tgz cmpsc311
% cd cmpsc311
% tar xvfz assign2-starter.tgz
% cd assign2
% make
Install libraries
• You will have to install some libraries you will need for the assignment. Run
the following command in your terminal window.
sudo apt-get install libcurl4-gnutls-dev libgcrypt-dev
Hints
• Use the logMessage interface to
log information about how your
program is running. (see next
page)
• Carefully read and understand the
error messages that are being
written to the log.
• Review the simulator code to see
how the interfaces in the program
should operate.
!!!!
logMessage()
• Available in the cmpsc311_log.h – provides you a way to print out
information from your code, and works like printf()
‣ logMessage( LEVEL, “Stuff … %d”, parameters );
‣ Use the “LcDriverLevel” level for your code (global value)
logMessage(lcDriverLevel, “This is my code %d [%s]”, val, str );
Open() pseudo-code
Open (path) {
1) check if file already open
(fail if already open)
2) pick unique file handle
3) save filename and file information locally
4) set file pointer to first byte
5) if file not exists
set length to 0
return file handle
}
Read() pseudo-code
Read ( file handle, length, buffer ) {
1) check if file handle valid (is associated with open file)
2) check length to if it is valid
3) figure out what device/sector/block data for the read is
4) get the block
5) copy the data from the xfer block to buffer
6) update the buffer length
return the number of read bytes
}
First functions …
• The first functions you should write should create a register structure and
extract a register structure:
LCloudRegisterFrame create_lcloud_registers(…?) {
???
}
??? extract_lcloud_registers(LCloudRegisterFrame resp, …) {
???
}
Hint: use the bit operations to build packed registers ….
Packing
• To pack the values (variables b0, b1 ….), you need to combine some set of
shift operations and bitwise (&)
B0 C0 C1 C2 D0 D1
4-bits 8-bits 8-bits 8-bits 16-bits 16-bits
B1
Most significant bit Least significant bit
Hint:
a = 0011
b = 0011
c = (b<<2) & a
Now : c = 1111
Doing an operation
• For each operation, say LC_POWER_ON
1. Pack the registers using your create_lcloud_registers function
2. Set the xfer parameter (NULL for power on)
3. Call the lcloud_io_bus and get the return registers
4. Unpack the registers using your extract_lcloud_registers function
5. Check for the return values in the registers for failures, etc.
Doing an operation
• Example from PDM’s implementation of the filesystem
‣ the variable names should tell you something about what is going one)
‣ This particular code contains an operation into WRITE into the device …
‣ buf is a 256 byte character array (see last lecture)
/* Do the write operation, check result */
frm = create_lcloud_registers(0, 0, LC_BLOCK_XFER, did, LC_XFER_WRITE, sec, blk );
if ( (frm == -1) || ((rfrm = lcloud_io_bus(frm, buf)) == -1) ||
(extract_lcloud_registers(rfrm, &b0, &b1, &c0, &c1, &c2, &d0, &d1)) ||
(b0 != 1) || (b1 != 1) || (c0 != LC_BLOCK_XFER) ) {
logMessage( LOG_ERROR_LEVEL, "LC failure writing blkc [%d/%d/%d].", did, sec, blk );
return( -1 );
}
What you are doing (visually) ….
• Initially you will start with empty devices, all blocks are free.
• Once you power things on and process the open, you will see writes
• For this example, we are ignoring reads but it should be clear how to do
reads once you understand how to do writes.
• On the first write (#1) you will pick a block (any block, it is up to you).
• For the sake of this example, the write is exactly one block in size.
• You pick sector 0, block 0 (for one strategy), and write the block to it …
WR #1
• On the second write (#2) you will pick a block (any block, it is up to you, but you can’t pick
0,0 because it already has file data)
• For the sake of this example, the write is exactly one half block in size.
• You pick sector 1, block 2 (for one strategy), and write the block to it … BUT you have to
remember you have only used the first half of that block …
• On the third write (#3) you start by filling up what is unused by the previous
write in the block 1,2
• This write is one block long, so you split it into TWO writes the first half to 1,2
and the second half to a new block s-1, 1 (again up to you)
WR #1 WR #2 WR #3 WR #4
• And so on … i.e., as you add to the file you just allocate more blocks.
• Reads are the same, only you don’t do allocation, you just figure out how to read
the bytes from the blocks in one or more reads from the device.
• The whole assignment revolves around piecing together the reads/writes from
blocks.
Questions asked:
• Q: In the lcseek function, I am still unable to understand the phrase in the
slides 'The function should set the current position into the file to loc, where
0 is the first byte in the file'. Is loc referring to 'off' in size_t off? If so, does
this mean that off has to be equal to something?
• A: off is the “offset from zero”, so it is setting the absolute location. So,
‣ lcseek(10) - sets the file position to the 10th byte
‣ Lcseek(1000) - sets the file position to the 1000th byte

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