Intro to DFS assignment

Announcements DFS (PA4) Part 1 will be out over the weekend Part 1 Due 10/30 11:59 pm Part 2 12/7 11:59 pm Part 3 12/14 11:59 pm Part 4 (optional extra credit) 12/23 11:59pm

You build a DFS! 1. Lock server, at-most-once RPC semantics 2. Implement extent server; create/lookup/readdir FUSE ops 3. Implement read/write/open/setattr 4. Implement mkdir/unlink, integrate locks! (optional)

Programming Assignment: YFS Yet-another File System. :) Simpler version of what we just talked about: only one extent server (you don’t have to implement Petal; single lock server)

Part 1: lock server Implementing the lock server Provide mutual exclusion to ‘lock resources’ Using pthread mutexes, condition variables! Implementing at-most-once RPC semantics

Providing mutual exclusion over the net In the assignment: lock is a 64-bit number Client might: acquire(lock_a); do work; release(lock_a); You must create the lock if it doesn’t yet exist on the server

Example tester %./lock_tester 3772 simple lock client acquire a release a acquire a release a acquire a acquire b release b release a test2: client 0 acquire a release a test2: client 2 acquire a release a...

What’s provided Simple RPC framework, skeleton for lockserver code What it does: handles setting up sockets, marshalling/unmarshalling basic data types, sending over TCP (whew) What it doesn’t: does not keep track of RPC request state; duplicate RPCs are invoked twice! :(

Example RPC call

Your job for lock server

Lossy RPC_LOSSY: drops, duplicates, delays. Run lock_tester with RPC_LOSSY=0 Now try running it with RPC_LOSSY=5 Simulates network failure it should hang or error. FAIL!

Why? No at-most-once RPC semantics implemented...yet. If reply dropped, duplicate sent: acquire(a), acquire(a)

Strawman Remember every RPC call Client sends a unique RPC identifier Remember every RPC reply To avoid invoking the actual function What’s the problem with this approach?

Sliding window RPCs Assume the following sent by client: marshall m1 << clt nonce // client id << svr nonce // server id << proc // procedure number (bind, acquire, etc). << myxid // unique request id for this RPC << xid_rep_window.front() // Last out-of-order RPC reply received << req.str(); // Data But we need some additional info from the client

At the end % export RPC_LOSSY=5 %./lock_server 3772 & %./lock_tester all tests passed %./rpctest simple_tests... all tests passed

Helper functions Method_thread

Code reading

Part 2 Extent server FUSE! Semantics of filesystem calls

Programming Assignment: YFS Part 1: lock server Part 2: extent server

The extent server Don’t have to deal with storing data on disk: you will store contents in memory map All yfs_client operations synchronize with same extent server

Getattr (given)

Your job Extend extent_server to support put(extentid, string,...) get(extentid, string&) remove(extentid,...) See extent_protocol.h and extent_smain.cc Later you will likely add more! Must properly deal with ctime/atime/mtime

Data formats at extent server Directories maintain a mapping of filenames to inode numbers if root (inode 1) has two files “file1”, “file2”: get(1) might return file1: file2: You can choose how you store this information as a string

Metadata time mgmt atime: access time Updated whenever file contents accessed Set to 0 on file creation mtime: modification time Updated when file contents modified ctime: change time Updated whenever metadata modified

FUSE

Mapping FUSE functions

Example Fuse.cc void fuseserver_getattr(

CREATE/MKNOD Generate inode number (rand()) This is called on files: make sure inode has MSB set to 1 Directories have MSB set to 0 Create the file at the extent server Add the name to inode mapping to parent info at extent server

Lookup Given: filename, parent inode Look through parent directory list Find inode that maps from filename Getattr on that inode Fill in return structure (fuse_entry_param)

Readdir Given: inode number for a directory Get filename:inode mapping for that dir For each filename:inode pair call dirbuf_add(...) function provided

You will be able to create empty files in the root directory and do an ls on the root You’re not yet storing files...

Testing./start.sh./test-lab-2.pl./stop.sh test-lab-2.pl creates a bunch of files, tests whether the files the script created are there

Parts 3 and 4 Part 3: You implement open, read, write, setattr Part 4: You implement mkdir, unlink, and locking